Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
I I COSMIC RAYS PROGRAM Cosmic Ray Equipment Ready f o r Launch
COSMIC RAYS PROGRAM Page A. Organization of Technical Panel on Cosmic Rays 57 B. Summary of Panel Actions 58 C. Project Objectives and Results 62 2.2 C o r r e l a t i o n of Solar A c t i v i t y w i t h Primary Cosmic-Ray I n t e n s i t y . 63 2.3 Shipboard Neutron Monitor Station 65 2.4 Balloon F l i g h t s - La t i t u d e Survey 68 2.5 A i r Shower Detector 70 2.6 Ground Monitor Stations 71 2.7 Shipboard Neutron Monitor 72 2.8 Measurements of Primary Cosmic Radiation 73 2.9 Mu-Meson Monitor i n the A n t a r c t i c 77 2.11 Study of High Speed Cosmic-Ray Fluctuations 78 2.12 Cosmic-Ray I n t e n s i t y a t High A l t i t u d e 79 2.13 Low Energy Heavy Primary Cosmic Rays 86 2.14, 2.15 - Atmospheric, Geomagnetic and Solar Influences on the Mu-Meson and Nucleonic Components of the Cosmic Radiation 87 2.16 Neutron Monitor - Alaska 92 2.17, 2.18 - High A l t i t u d e Study o f Spectrum and Time V a r i a t i o n of Neutrons and Primary Radiation 93 2.19 Balloon Emulsion Studies of Heavy Primary Cosmic Rays 95 2.21 The Semi-Diumal Planetary V a r i a t i o n of Atmospheric Pressure . . 97 2.22 I s o t r o p i c C o n s t i t u t i o n of Cosmic Radiation a t Balloon A l t i t u d e s . 99 2.23 Heavy Primary Cosmic Rays 103 2.24 Measurement of Zenith-Angle Dependence on High-Energy Mu-Mesons . 108 2.25 Solar E f f e c t s on Cosmic Rays a t High A l t i t u d e s - A r c t i c I l l 2.28 Neutron Monitor - Thule 114 2.29 Energy and Charge Spectrum of Primary Cosmic Radiation 115 2.30 Neutron I n t e n s i t y Time Va r i a t i o n s 118 2.32 Reduction and Analysis of Cosmic-Ray Data 120 2.33 Cosmic-Ray Tr a j e c t o r y Computation and Study 121 2.34 Reduction of Cosmic-Ray I o n i z a t i o n Chamber Data 122 56
I I . COSMIC RAYS PROGRAM A. Organization of Technical Panel on Cosmic Rays 1. Establishment of the Panel. L e t t e r s were w r i t t e n i n December 1954 to p h y s i c i s t s working on cosmic ray research asking them to p a r t i c i p a t e i n the planning f o r the U.S. e f f o r t by serving as members of the Technical Panel on Cosmic Rays. Dr. Serge A. K o r f f convened the f i r s t meeting, at which Scott E. Forbush was elected Chairman and Serge A. K o r f f Secretary, at a l a t e r date, Dr. K o r f f was named Vice-Chairman. The panel rec- ommended that J.A. Van A l l e n be i n v i t e d to become a member. Several s c i e n t i s t s were asked to be consultants to the panel and the Department of Defense appointed l i a i s o n members from the three services. The panel makeup was as follows: 2. Composition of the Panel. ( A f f i l i a t i o n at time of appointment.) Panel Members S.E. Forbush, Chairman S.A. K o r f f , Exec. Vice-Chm. H.V. Neher E.P. Ney J.A. Simpson S.F. Singer A. Van A l l e n Sec. and Department of T e r r e s t r i a l Magnetism, Carnegie I n s t i t u t i o n of Washington New York U n i v e r s i t y C a l i f o r n i a I n s t i t u t e of Technology Un i v e r s i t y of Minnesota U n i v e r s i t y of Chicago Un i v e r s i t y of Maryland State U n i v e r s i t y of Iowa b. Consultants W. Ott i n g R.R. Heer, J r . W.S. McAffee, J r . M.M. Shapiro Douglas L. Worf R.J. Mackin ( t o July 1955) S.C. Daubin (July 1955 to July 1957) A.G. Opitz (July 1957 to July 1959) Ai r Force O f f i c e of S c i e n t i f i c Research A i r Force O f f i c e of S c i e n t i f i c Research U.S. Army Signal Res. & Dev. Lab. U.S. Naval Research Laboratory Atomic Energy Commission O f f i c e of Naval Research O f f i c e of Naval Research O f f i c e of Naval Research c. Secre t a r i a t (IGY S t a f f ) G.F. S c h i l l i n g (Jan. 1955 - July 1956) J.H. DePue (July 1956 - July 1957) P.W. Mange (July 1957 - Feb. 1959) Stanley Ruttenberg (From February 1959) 3. Panel Meetings. There were eight meetings of the panel. F i r s t Meeting Second Meeting Third Meeting Fourth Meeting F i f t h Meeting S i x t h Meeting Seventh Meeting Eighth Meeting January 20-21, 1955 February 21, 1955 A p r i l 27, 1955 July 13-14, 1956 December 10, 1956 A p r i l 24, 1957 November 1, 1957 November 29, 1958 Washington, D.C. Washington, D.C. Washington, D.C. Boulder, Colorado Washington, D.C. Washington, D.C. Washington, D.C. Chicago, I l l i n o i s 57
COSMIC RAYS B. Summary of Panel Actions 1. O r i g i n a l Program. I n c o n s u l t a t i o n w i t h U.S. s c i e n t i s t s working i n the f i e l d of cosmic rays and t h e i r geophysical i m p l i c a t i o n s , the USNC developed a general program th a t took i n t o account the CSAGI recommendations and the i n t e r e s t s of U.S. s c i e n t i s t s . S.A. K o r f f was the U.S. National Reporter f o r Cosmic Rays i n t h i s e a r l y planning period. The i n i t i a l general program was developed to supply information on three categories of problems. a. Mass and Energy Spectrum. I t was proposed to send a l o f t nuclear emulsion stacks and a v a r i e t y of counters to study the heavy primaries and to f u r t h e r the know- ledge of the primary energy d i s t r i b u t i o n . b. The Low Energy End of the Spectrum. I t was known th a t a low energy c u t - o f f p revailed depending on geomagnetic l a t i t u d e , but the character of the low energy end of the spectrum and the nature of the c u t - o f f was not w e l l known. The behaviour of the c u t - o f f , e s p e c i a l l y the shape of the spectrum, the i n t e n s i t y of p a r t i c l e s , and the geomagnetic dependence, was to be investigated as the solar a c t i v i t y rose to maxi- mum, f o r comparison w i t h studies being c a r r i e d out ( a c t u a l l y during the IGY planning period) at solar a c t i v i t y minimum. Balloons, rockets and a i r c r a f t were proposed as means of carr y i n g equipment to various atmospheric l e v e l s f o r various lengths of ex- posure. I t was also proposed to carry out l a t i t u d e surveys of the low energy p o r t i o n of the spectrum using a i r c r a f t and balloons. c. Cosmic-Ray Fluctuations. To study the f l u c t u a t i o n s of i n t e n s i t y , and to cor- r e l a t e these w i t h solar disturbances and w i t h geophysical phenomena such as magnetic disturbances, i t was proposed to e s t a b l i s h a network of continuously recording moni- t o r s , measuring the nucleonic and mesonic components of the secondary f l u x , as w e l l as the t o t a l i o n i z a t i o n . I t was also planned to make special balloon and rocket observa- t i o n s during f l u c t u a t i o n s i n the cosmic-ray i n t e n s i t y . A number of other experiments were also suggested as perhaps appropriate to the IGY program. These included several studies of heavy primaries, such as i n t e n s i t y v a r i a t i o n s during solar disturbances and time f l u c t u a t i o n s of p a r t i c l e s w i t h energies near to the geomagnetic c u t - o f f , cosmic-ray bursts i n i o n i z a t i o n chambers f o r a study of phenomena r e l a t e d to energies of about 10 ev; searches f o r a n t i - p a r t i c l | s ; balloon expeditions to remote l o c a t i o n s , the search f o r |aiiima rays of energy 2 x 10 ev from the sun, which would i n d i c a t e the formation of H by neutron capture; and possibly measurements i n the e q u a t o r i a l region looking f o r d i u r n a l e f f e c t s . 2. Early Planning. One of the f i r s t actions of the Panel was to review the program suggested by the U.S. National Committee and discuss s p e c i f i c p r o j e c t proposals. Let- t e r s were addressed to about f i f t y s c i e n t i s t s i n the United States working on cosmic- ray problems. This was to inform them of the IGY objectives and to make known the opportunity to p a r t i c i p a t e i n the program. a. A n t a r c t i c Program. Inasmuch as the lead time f o r a n t a r c t i c observations was considerably longer than f o r other programs, the Panel was requested to make prompt recommendations f o r p r o j e c t s . Monitor observations at the main s t a t i o n and balloons launched from shipboard en route to A n t a r c t i c a were considered desirable. The Panel discussed the f a c i l i t i e s that would be needed and made suggestions f o r the b e n e f i t of the Navy (Task Force 43) which was assigned t o supply l o g i s t i c support f o r the ant- a r c t i c program. Later developments i n the U.S. program increased the a n t a r c t i c pro- gram to s i x f u l l s t a t i o n s . The Panel then approved cosmic-ray observations at two locations -- a meson telescope at Wilkes and a neutron monitor and meson telescope at 58
COSMIC RAYS Ells w o r t h . The Panel also discussed the d e s i r a b i l i t y of exploratory cosmic-ray meas- urements i n the A n t a r c t i c . Accordingly, i t was recommended that a neutron monitor be i n s t a l l e d aboard the USS ATKA during the 1955-56 exploratory cruise. This work proved to be h i g h l y u s e f u l . I n f a c t , the monitor aboard the ATKA reported the great cosmic- ray event of February 23, 1956, while at anchor i n Wellington. The Panel recommended that t h i s p r o j e c t be continued i n succeeding years and the equipment was t r a n s f e r r e d to the USS ARNEB. b. General Program Recommendations. The Panel recommended that high l e v e l meas- urements w i t h balloons be c a r r i e d out i n e q u a t o r i a l regions. A r e s o l u t i o n was adopted expressing the hope that the Navy could undertake an expedition w i t h an a i r c r a f t car- r i e r to the e q u a t o r i a l regions, f a c i l i t i e s of which would be made av a i l a b l e to the various groups working w i t h balloons. I t was not possible during the IGY f o r the Navy to undertake such an expedition; however, a series of launchings was supported by the Navy from Guam, during which many i n v e s t i g a t o r s p a r t i c i p a t e d . c. Sky-Hook Program. The Panel adopted a recommendation expressing the hope that the Navy would continue to support the launching of sky-hook balloons through the IGY period i n order to provide as many heavy payload, high a l t i t u d e f l i g h t s as possible. d. L i a i s o n w i t h Canadian S c i e n t i s t s . During the discussion of appropriate ex- periments, I t was r e a l i z e d t h a t e f f e c t i v e coordination should be established between U.S. and Canadian cosmic-ray s c i e n t i s t s . The Panel requested Dr. Simpson to contact Dr. D.C. Rose of Canada to explore coordination between U.S. and Canadian workers. I n view of the CSAGI recommendation of the establishment of cosmic-ray moni- t o r s at a wide range of l a t i t u d e s , and taking i n t o account the existence of s t a t i o n s i n the United States, the panel f e l t t h a t i t would add g r e a t l y t o the proposed net- work should a new s t a t i o n be established at Ft. C h u r c h i l l , Canada. Accordingly, the Panel requested Dr. Simpson to ascertain from Dr. Rose whether the Canadians might be i n t e r e s t e d i n e s t a b l i s h i n g such a monitor. e. Continuous Monitoring at the Top of the Atmosphere. The Panel discussed the d e s i r a b i l i t y of maintaining as continuous a monitor as possible of cosmic-ray i n t e n - s i t y at high a l t i t u d e s . I t was recommended th a t a program of t h i s type be undertaken during the IGY. 3. Li a i s o n . a. Solar A c t i v i t y . The Cosmic-Ray Panel noted that the solar information made avai l a b l e through the p u b l i c a t i o n s of the National Bureau of Standards was most useful to cosmic-ray workers and expressed the hope that the a v a i l a b i l i t y of such data could be continued through the IGY. The solar f l a r e p a t r o l proposed f o r the IGY was discussed and the Panel ex- pressed the hope that p a t r o l a c t i v i t y could be increased f o r the IGY period. I n par- t i c u l a r , i t was pointed out that there appeared to be a gap i n the coverage i n the A t l a n t i c area. b. World Days and Communication. A representative of the IGY World Warning Agency (AGIWARN, which was established f o r the IGY by the National Bureau of Standards) de- scribed f o r the Panel the services which AGIWARN could provide and the planning at th a t time f o r communication f a c i l i t i e s which AGIWARN would be able to use to provide information to observers. The Panel discussed the kinds of information and the time scale of d e l i v e r y that might be desirable. For example, i t was f e l t t hat information on Class 2 f l a r e s might be supplied by telegraph but t h a t Class 3 and 3+ f l a r e s should 59
COSMIC RAYS be communicated to c e r t a i n cosmic-ray observers by phone c a l l w i t h the least possible delay. I t was also suggested t h a t AGIWARN undertake to supply information on balloon and rocket launchings so tha t other observers might coordinate t h e i r observations. 4. Implementation of Program. I n view of the general program plans developed by the U.S. National Committee, the Panel reviewed p r o j e c t proposals and developed the pro- gram as represented by the various p r o j e c t s discussed i n part B of t h i s chapter. I n some instances the Panel suggested where there might be a useful a d d i t i o n to the pro- gram; f o r example, i t was suggested that an a i r shower detector on the West Coast sim- i l a r to t h a t operated at the U n i v e r s i t y of Maryland, would be a valuable a d d i t i o n to the program. This work was undertaken at the U n i v e r s i t y of C a l i f o r n i a , Santa Barbara. The Panel at one time f e l t t h a t a f u l l time coordinator would be able to assi s t the various groups i n working out balloon programs and other experiments r e q u i r i n g co- or d i n a t i o n of e f f o r t . A search was made f o r a su i t a b l e young cosmic-ray s c i e n t i s t who might be w i l l i n g to devote a year or so of hi s time to the program. Such a person was not found and the funds t e n t a t i v e l y earmarked were released to support observational p r o j e c t s . One p r o j e c t , a neutron monitor i n Puerto Rico, was not c a r r i e d out to completion owing t o the serious i l l n e s s of the p r o j e c t d i r e c t o r , Dr. L e t t i c i a Rosario, which pre- vented her from coiiq>leting the assembly of the equipment. 5. Regulations Regarding Ballooning. The ONR representative, R.J. Mackin (and l a t e r 5. Daubin) discussed w i t h the Panel the regulations regarding a i r safety as they a f - fected the launchings of balloons. Through the information supplied by the Panel, then, the various workers were able to plan t h e i r balloon launchings so as to comply w i t h the safety regulations f o r small payload balloons and to secure the proper auth- o r i t y f o r the release, usually through Navy or contractor f a c i l i t i e s , of heavy payload balloons. The ONR also o f f e r e d valuable assistance to balloon launching groups i n the matter of l i c e n s i n g of telemetering equipment and the procurement of helium through Navy channels, f o r which reimbursement had to be arranged. 6. Technical Manuals. The Panel discussed the standardization of monitor equipment and concurred w i t h the CSAGI recommendation th a t the neutron monitor equipment be as described i n the r e p o r t e n t i t l e d "Cosmic-Ray Neutron I n t e n s i t y Monitor" by John A. Simpson, and the recommendations of the lUPAP w i t h regard to meson telescopes. The Panel also recommended th a t the CERN report "Standardization of Nuclear Emulsion Techniques" be made part of the cosmic-ray t e c h n i c a l manual. 7. P u b l i c a t i o n P o l i c y . I n preparation f o r the I l i r d Assembly of the CSAGI i n Brussels i n 1955, the Panel discussed the exchange of cosmic-ray data and recommended that the f o l l o w i n g data be exchanged among p a r t i c i p a t i n g countries: a. D a i l y and b i - h o u r l y means of meson and neutron i n t e n s i t y as determined w i t h lUPAP standard instruments, both before and a f t e r c o r r e c t i o n f o r meteorological e f f e c t s . The c o e f f i c i e n t s and procedures employed i n c o r r e c t i n g the data should be published i n d e t a i l . b. Other r e s u l t s obtained as part of the IGY program should be published i n the appropriate t e c h n i c a l j o u r n a l s as soon as f e a s i b l e . c. A l l data from IGY supported p r o j e c t s should be a form s u i t a b l e f o r d i s t r i b u - t i o n and p u b l i c a t i o n w i t h i n a year a f t e r the termination o f the IGY. For some special observations, f o r example, balloon and rocket f l i g h t s , should be summarized and a pre- l i m i n a r y report prepared as soon as possible. This would be followed l a t e r by the 60
COSMIC RAYS usual s c i e n t i f i c p u b l i c a t i o n . 8. Cosmic-Ray Work i n South America. Dr. Serge K o r f f discussed w i t h the Panel the v i s i t s he had made to various South American la b o r a t o r i e s during a t r i p which he made w i t h E.O. Hulburt. Some l e t t e r s were addressed to colleagues i n South America expressing i n t e r e s t i n t h e i r work. 9. T r a n s l a t i o n of USSR Tr e a t i s e . A book by the USSR s c i e n t i s t L . I . Dorman on cosmic- ray i n t e n s i t y v a r i a t i o n s was brought to the a t t e n t i o n of the Panel, which expressed the hope th a t i t would be possible to t r a n s l a t e t h i s Important volume and make i t av a i l a b l e to cosmic-ray workers. The t r a n s l a t i o n was f i n a l l y accomplished through the cooperation of the A i r Force O f f i c e of S c i e n t i f i c Research. 10. Data Reduction and I n t e r d i s c i p l i n a r y Research. Acting upon a request of the Executive Committee, the Panel queried the various p r o j e c t d i r e c t o r s w i t h regard to whether they had s u f f i c i e n t funds to provide f o r the reduction of data m the rec- ommended form and the supplying of copies t o the World Data Centers. Recommendations were made to the Executive Committee f o r Increases m several p r o j e c t s t o pennit the reduction of data to meet the o b l i g a t i o n s of data exchange. The Panel also discussed means of applying c o r r e c t i o n s t o neutron and meson data, using IBM punch card tech- niques. Some discussions were held on the i n t e r d i s c i p l i n a r y analysis of the IGY cosmic- ray data and several proposals f o r s p e c i f i c programs were reviewed. These proposals were eventually supported through the I n t e r d i s c i p l i n a r y Research Committee under the chairmanship of M.M. Shapiro. Two other proposals of a d i f f e r e n t nature were also discussed. These p r o j e c t s Involved the support of distinguished senior s c i e n t i s t s from other countries to v i s i t the United States and be free to discuss w i t h t h e i r colleagues here the various a p p l i c a t i o n s of IGY data to the s o l u t i o n of geophysical problems. 11. Fellowships. The Panel discussed the d e s i r a b i l i t y of approaching the State Department and UNESCO w i t h a view toward s e t t i n g up fellowships f o r IGY s c i e n t i s t s , not only i n the United States but from abroad, to spend time v i s i t i n g other labora- t o r i e s and engage i n analyses of IGY data. The Panel adopted a r e s o l u t i o n to t h i s e f f e c t which was r e f e r r e d by the Execu- t i v e Committee to the other panels. As a consequence of t h i s a c t i o n , l e t t e r s were w r i t t e n to panel chairmen and many senior s c i e n t i s t s i n the United States asking f o r s p e c i f i c recommendations as to appropriate s c i e n t i s t s who could q u a l i f y f o r such fellowships. Discussions were also held w i t h other o f f i c e s i n the Academy knowledge- able about such fellowships and i n f o r m a t i o n was turned over t o appropriate groups. 12. Rights of I n v e s t i g a t o r s , The Cosmic-Ray Panel discussed the p r o t e c t i o n of the o r i g i n a l i n v e s t i g a t o r i n being given a s u f f i c i e n t length of time to analyze and pub- l i s h h i s data before he was required to submit i t t o the Data Center. The CSAGI was also aware of possible problems i n t h i s connection but recommended against the adop- t i o n of any procedure t h a t would lead to delay of p u b l i c a t i o n . The CSAGI, however, recommended that the Data Centers, i n response t o requests f o r data, s h a l l i d e n t i f y the I n v e s t i g a t o r responsible f o r the desired data and request t h a t the receiver of the data respect the usual r i g h t s of the o r i g i n a l i n v e s t i g a t o r p r i o r to the p u b l i c a - t i o n of data i n the "Annals o f the IGY." A f t e r such p u b l i c a t i o n of data i n the Annals, i t was f e l t t hat the o r i g i n a l r i g h t s of the I n v e s t i g a t o r need no longer be protected. 13. Recommendations f o r IGC 1959. When the CSAGI at i t s F i f t h Assembly i n Moscow i n 1959 adopted a recommendation c a l l i n g f o r the continuation of programs Insofar as f e a s i b l e by the p a r t i c i p a t i n g countries f o r 1959, the Panel was requested to comment on what might be appropriate to continue f o r another year. Proposals f o r extension 61
COSMIC RAYS of observations were received from most of the IGY p r o j e c t d i r e c t o r s which were r e - viewed by the panel and incorporated i n t o the USNC recommendations t o the National Science Foundation. C. Project Objectives and Results 1. Summary of Program. The cosmic-ray program supported a number of ground l e v e l monitors of two types, the nucleonic and meson detectors. Another important part of the program was concerned w i t h balloon f l i g h t s of both heavy and l i g h t payload. I n ad d i t i o n , there were a number of special experiments as w e l l as data reduction pro- j e c t s . 2. Order of Project Description. The pr o j e c t s that are described i n the f o l l o w i n g pages are i n numerical order to correspond w i t h the o r i g i n a l formulation of the pro- gram. For convenience, the p r o j e c t s are grouped below to r e f l e c t s i m i l a r i t y of pur- pose. Ground Level Monitors 2.6, 2.9, 2.10, 2.14, 2.15, 2.16, 2.28, 2.30 Balloons 2.2, 2.4, 2.8, 2.12, 2.13, 2.17, 2.18, 2.19, 2.22, 2.23, 2.25, 2.29 Cosmic-Ray Equator 2.3, 2.7, 2.33, 2.35 Shower 2.5 Rapid Fluctuations 2.11 Underground Telescope 2.21 Mu-Meson 2.24 Data Reduction and Analysis 2.32, 2.34 3. Cancelled Proiects. Former p r o j e c t s bearing the f o l l o w i n g numbers were eliminated from the program or combined w i t h other p r o j e c t s : 2.1, 2.20, 2.26, 2.27, 2.31. 62
COSMIC RAYS Project 2.2 - C o r r e l a t i o n of Solar A c t i v i t y w i t h Primary Cosmic-Ray I n t e n s i t y 1. Objectives. This p r o j e c t at B a r t o l Research Foundation was planned to e s t a b l i s h possible c o r r e l a t i o n s between the i n t e n s i t y of the primary cosmic r a d i a t i o n and solar a c t i v i t y as manifested, f o r example, by f l a r e s , r . f . r a d i a t i o n c h a r a c t e r i s t i c s . The method of measurement consisted of systematically sending to and maintaining at high a l t i t u d e s balloon-borne charged-particle detectors. 2. Operations. A mobile f i e l d s t a t i o n and a f i x e d ground s t a t i o n at Swarthmore were reconditioned f o r t h i s p r o j e c t . Balloon-borne instrument assemblies (counter t r a i n s and pulse i o n i z a t i o n chambers) were constructed, and a device f o r l e v e l l i n g o f f the neoprene balloons was developed. Standard type meteorological balloons were used w i t h the very l i g h t - w e i g h t instrument assemblies, successful nighttime f l i g h t s were achieved w i t h neoprene balloons. Two complete receiving s t a t i o n s and antenna systems were constructed so that two f l i g h t s could be launched, or a second f l i g h t launched before the f i r s t f l i g h t terminated. Telemetry was used, but the f l i g h t s were recov- ered where possible i n order to re-use the instrumentation. At Swarthmore, 78 f l i g h t s were made, of which 52 proved successful. Simultaneous releases were also made from Durham, N.C., and Tallahassee, F l o r i d a , where ten r e - leases r e s u l t e d m eight successful f l i g h t s . The c o u n t e r - t r a i n s c a r r i e d 7.5 cm of lead absorber. 3. Personnel. This work was under the supervision of Dr. M.A. Pomerantz. Som Prakash Agarwal and V.R. Potnis were also involved i n the experimental program. 4. Data. A l l data from these f l i g h t s have been sent to the World Data Centers. 5. Results. From the series of f l i g h t s at Swarthmore, i t was found that the primary f l u x was much lower than i n pre-IGY f l i g h t s . No enhancement of the cosmic-ray i n t e n - s i t y was observed i n any of these IGY f l i g h t s which contained 87 g/cm^ absorber, de- s p i t e the unusually high l e v e l of solar a c t i v i t y . This i s i n contrast w i t h e a r l i e r r e s u l t s , since on several occasions f l a r e associated increases were observed during the d e c l i n i n g p o r t i o n of the preceding solar cycle (1949-52). The present r e s u l t i s q u i t e s i g n i f i c a n t . F l i g h t s by other i n v e s t i g a t o r s , using less absorber, detected solar-induced e f f e c t s ; t h i s i s explicable by the steep energy spectrum of the solar- produced p a r t i c l e s . The monitoring of the primary f l u x at the top of the atmosphere, at energies beyond the range of solar p a r t i c l e s , revealed a high degree of v a r i a t i o n , i n contrast to the more-or-less s t a t i s t i c a l v a r i a t i o n i n the f l u x measurement during solar minimum. And, a clear 28^ 1 day recurrence tendency was found, which was f o l - lowed through several cycles, Thle i s i n t e r p r e t e d as a solar-induced modulation of the g a l a c t i c f l u x . The measuremeats c o r r e l a t e d w e l l w i t h the v a r i a t i o n s observed by sea l e v e l neutron monitors for corresponding f l i g h t days. The v a r i a t i o n s at a l t i t u d e were 1.6 ± 0.3 times those observed at sea-level. The pe r i o d i c v a r i a t i o n ended i n November 1957, and thence a more or less slow steady downward trend was observed, culminating i n the lowest i n t e n s i t i e s during the Durham-Swarthmore series of f l i g h t s . Simultaneous observations at the two s t a t i o n s showed the absence of any detectable l a t i t u d e e f f e c t , i n contrast w i t h the previous solar cycle. These fi n d i n g s are of considerable relevance to the deceleration or modulation mechanism that might explain t h i s behavior. 63
COSMIC RAYS 6. Bibliography. a. Papers Presented at Meetings. S.P. Agarwal, M.A. Pomerantz, V.R. Potnis: "Solar A c t i v i t y and the Primary Cosmic-Ray I n t e n s i t y . " B u l l . Am. Phys. Soc. v o l . 4, no. 5, A p r i l 30, 1959, p. 237. M.A. Pomerantz, S.P. Agarwal, V.R. Potnis: "Balloon F l i g h t I n v e s t i g a t i o n s of Primary Cosmic-Rays during Solar Disturbances." lUPAP I n t e r n a t i o n a l Congress on Cosmic-Rays, Moscow, July 6-11, 1959. b. Published Papers. M.A. Pomerantz, S.P. Agarwal, V.R. Potnis: "Direct Observations of Periodic V a r i a t i o n of Primary Cosmic-Ray I n t e n s i t y . " Phys. Rev., v o l . 109, no. 1, Jan. 1, 1958, pp. 224-5. M.A. Pomerantz, S.P. Agarwal, V.R. Potnis: "Nature of the Current Reduction m the Primary Cosmic-Ray I n t e n s i t y . " Phys. Rev. L e t t e r s , v o l . 1, no. 2, July 15, 1958, pp.65-68. M.A. Pomerantz, S.P. Agarwal: "Further Observations on the Nature of the Current Reduction i n the Primary Cosmic-Ray I n t e n s i t y . " Phys. Rev. L e t t e r s , v o l . 1, no. 3, Aug. 1, 1958, pp. 107-109. M.A. Pomerantz, S.P. Agarwal, V.R. Potnis: "Balloon F l i g h t I n v e s t i g a t i o n s of Primary Cosmic Rays during Solar Disturbances." Journ. F r a n k l i n I n s t . , v o l . 269, no. 3, March 1960, pp. 235-244. 64
COSMIC RAYS Project 2.3 - Shipboard Neutron Monitor S t a t i o n 1. Objectives. A neutron monitor s u i t a b l e f o r shipboard operation was constructed at the B a r t o l Research Foundation i n close c o l l a b o r a t i o n w i t h Dr. D.C. Rose of the National Research Council of Canada. The other p a r t i c i p a n t i n t h i s i n t e r n a t i o n a l c o l l a b o r a t i o n was Uppsala U n i v e r s i t y , Sweden (A.E. SandstrUm). I n a d d i t i o n to pro- v i d i n g data relevant to the determination of the geomagnetic coordinates, the "mobile" s t a t i o n also served the same fu n c t i o n as the established world-wide chain of f i x e d sea- l e v e l monitors i n i n v e s t i g a t i o n s of c o r r e l a t i o n s of the cosmic-ray i n t e n s i t y w i t h solar and geomagnetic a c t i v i t y , time v a r i a t i o n , etc. 2. Operations. A neutron p i l e of the same s p e c i f i c a t i o n s and using s i m i l a r counters as the instrument which had been u t i l i z e d by the Canadian NRC f o r conducting ship- board observations was i n s t a l l e d , as a cooperative experiment, on a ship of Swedish r e g i s t r y ( T r a n s a t l a n t i c Company of Sweden). The ship's course was down the west coast of A f r i c a . Later, the instrument was tra n s f e r r e d to a second vessel which f o l - lowed a s i m i l a r course and also crossed the geomagnetic equator i n the Indian Ocean. Thus, ten crossings of the equator during the IGY gave a series of l a t i t u d e p r o f i l e s of cosmic ray i n t e n s i t y . (See F i g . 1 f o r d e t a i l s of tracks.) 3. Personnel. The p r o j e c t was under the d i r e c t i o n of M.A. Pomerantz of B a r t o l ; D.C. Rose, National Research Council of Canada and A.E. SandstrHm, U n i v e r s i t y of Uppsala, Sweden, cooperated i n supplying equipment and making the arrangements f o r the experi- ment, re s p e c t i v e l y . S c i e n t i s t s from Swedish U n i v e r s i t i e s served as observers on the various cruises. V.R. Potnis of B a r t o l Research Foundation reduced the data. 4. Data. Standard reductions were c a r r i e d out on the data at Uppsala and Swarthmore, and the r e s u l t s submitted to the IGY World Data Centers. 5. Results. The l o c a t i o n of the cosmic-ray equator o f f the west coast of A f r i c a i n the A t l a n t i c Ocean was established as 6.7±0.8°N at 14''W longitude; and i n the Indian Ocean as 6.3i0.4°N at 60''E longitude. This does not agree w i t h the conventional geo- magnetic equator, or even w i t h the l o c a t i o n predicted on the basis of the various dip o l e approximations. Although the mean value of the cosmic-ray i n t e n s i t y minimum coincides w i t h the observed p o s i t i o n of the i s o c l i n i c equator ( d i p angle equal to 0°) at 14''W, I t d i f f e r s i n geographic l a t i t u d e by 2° i n the v i c i n i t y of 60''E. The d i s - crepancy exceeds the experimental u n c e r t a i n t i e s . Although solar and geophysical a c t i v i t y v aried considerably during t h i s period, the l o c a t i o n of the cosmic-ray equator at 14°W appears to have remained f i x e d w i t h i n approximately 1°. However, the p o s s i b i l i t y of a small progressive change of about the magnitude of the uncertainty cannot be precluded. The r e l a t i o n s h i p s between isocosms and various representations of the earth's magnetic f i e l d are being studied, so as to obtain as complete a glo b a l map as possible. 6. Bibliography. a. Papers Presented at Meetings. M.A. Pomerantz, A.E. SandstrBm, and D.C. Rose: "Shipboard Neutron Monitor Determination of Cosmic-Ray Equator." lUPAP I n t e r n a t i o n a l Congress on Cosmic-Rays, Varenna, June 21-26 (1957). 65
COSMIC RAYS M.A. Pomerantz, A.E. SandstrOm, V.R. Potnis, D.C. Rose: "Solar Disturbances and the Cosmic-Ray Equator." lUPAP I n t e r n a t i o n a l Congress on Cosmic-Rays, Moscow, July 6-11, 1959. M.A. Pomerantz, A.E. SandstrOm, V.R. Potnis: "Shipboard Neutron Monitor I n v e s t i g a t i o n s of Relationships between Cosmc-Ray I n t e n s i t y and the Earth's Magnetic F i e l d . " X l l t h General Assembly, I n t e r n a t i o n a l Union of Geodesy and Geophysics, H e l s i n k i , Finland, July 26-Aug. 6 (1960). b. Published Papers. M.A. Pomerantz, A.E. Smith: "Automatic Counting-Rate Recorder." Nuclear Instruments, v o l . 2, 1958, pp. 49-52. M.A. Pomerantz, A.E. SandstrBm, and D.C. Rose: "Shipboard Neutron-Monitor Determination of Cosmic-Ray Equator." Nuovo Cimento (10) Suppl. v o l . 8, 1958, pp. 257-62. M.A. Pomerantz, A.E. SandstrBm, V.R. Potnis, D.C. Rose: "Solar Disturbances and the Cosmic Ray Equator." T e l l u s . v o l . X I I , no. 6, 1960, pp. 231-35. M.A. Pomerantz, V.R. Potnis, A.E. SandstrOm: "The Cosmic-Ray Equator and the Earth's Magnetic F i e l d . " JGR, v o l . 65, no. 11, I960, pp. 3539-43. M.A. Pomerantz: "Sea-Going Cosmic-Ray Observatory." J. F r a n k l i n I n s t . . v o l . 263, no. 2, February 1957, pp. 153-159. M.A. Pomerantz: "Sea-Gomg Cosmic-Ray Observatory." Research Reviews. December 1957, pp. 1-5. Arne Eld SandstrOm, Martin A. Pomerantz, and Bengt-Olov Gronkvist: " L a t i - tude E f f e c t and Atmospheric Attenuation of the Cosmic Ray Nucleon Component." Te l l u s . v o l . XIV, no. 3, pp. 356-362, (1962). Arne Eld SandstrOm, Martin A. Pomerantz, and Bengt-Olov Gronkvist: "Sea Level Cosmic Ray I n t e n s i t y and Threshold R i g i d i t y . " T e l l u s . v o l . XV, no. 2, pp. 184-193, (1963). 66
COSMIC RAYS M/S LOHMAREN H/S S T R A T U S Figure 1. Routes of Ships LOMMAREN and STRATUS 67
COSMIC RAYS Project 2.4 - Balloon F l i g h t s - L a t i t u d e Survey 1. Objectives. This p r o j e c t at the C a l i f o r n i a I n s t i t u t e of Technology was planned to repeat at sunspot msiximum c e r t a i n measurements of the primary cosmic-ray f l u x obtained i n 1954, near sunspot minimum, and to extend these observations over a wide l a t i t u d e range, w i t h a view to studying: a. The l a t i t u d e e f f e c t , i n c l u d i n g the c u t - o f f or "knee" at high a l t i t u d e s , b. Fluctuations i n the primary r a d i a t i o n i n e q u a t o r i a l regions compared w i t h those at the higher l a t i t u d e s , c. Possible asymmetry conditions e x i s t i n g between the poles or the poles and the equator, d. The o v e r - a l l p i c t u r e of cosmic-ray phenomena at high a l t i t u d e s at t h i s par- t i c u l a r phase of the solar cycle compared w i t h other phases. 2. Operations. A large number of omni-directional i o n i z a t i o n chambers designed by H.V. Neher, barometric switches and associated e l e c t r o n i c s f o r telemetry were assem- bled i n t o i d e n t i c a l , l i g h t - w e i g h t f l i g h t sets. Moderate-sized rubber balloons were used so as to f a c i l i t a t e handling. I n July and August 1957 a series of f l i g h t s was made from Thule, Greenland. I n 1958 during July and August, releases were made on a ship voyage to Thule, while simultaneous c o n t r o l f l i g h t s were made from a temporary f i e l d l o c a t i o n near Bismarck, N.D. I n the f a l l of 1958, f l i g h t s were made from a U.S. Navy Task Force 43 vessel en route to New Zealand and the A n t a r c t i c , while simultaneous f l i g h t s , i n cooperation w i t h New Zealand s c i e n t i s t s , were made from I n v e r c a r g i l l , N.Z., as c o n t r o l s . I n a l l , 76 f l i g h t s were made from June 22 to December 22, 1958. 3. Personnel. This work was under the d i r e c t i o n of H.V. Neher, assisted by Hugh Anderson. 4. Data. The telemetered data were worked up t o give the r a t e of i o n i z a t i o n , which was tabulated f o r selected values (ranging from 500 to 5 g/cm"^) of a i r pressure. These tabulated data were submitted to the IGY World Data Center, w i t h l o c a t i o n , date and time of each f l i g h t noted. 5. Results. Some of the r e s u l t s that came out of the balloon f l i g h t s using i o n i z a - t i o n chambers are as follows: a. A large decrease i n i n t e n s i t y , compared w i t h other years, was found. At high l a t i t u d e s the loni z a t i o n - d e p t h curve passed through a maximum at about 50 g/cm-2 pressure. No maximum was found f o r s i m i l a r f l i g h t s i n 1951, 1954, 1955, or 1956. The i o n i z a t i o n at 15 g/cm' i n 1957 was 0.50 of i t s value i n 1954, the area under the ioniz a t i o n - d e p t h curve was down by 34 percent, and the number of primary p a r t i c l e s was down by a f a c t o r of four. This l a t t e r f i g u r e was obtained by comparing the 1957 data w i t h those obtained i n previous years at Thule, Greenland and at other l o c a t i o n s . By 1958, the number of primaries was down by a f a c t o r of f i v e . b. A comparison was made between the f l u c t u a t i o n s found by Forbush at Huancayo, Peru, w i t h the balloon data at Thule. For each year the f l i g h t s made at Thule were averaged, and the value at 15 g/cm*^ was then compared w i t h the yearly average at Huancayo. The Thule data were a l l taken during the middle of the summer period. 68
COSMIC RAYS namely around August 1. c. The cosmic-ray i n t e n s i t y , i n the longitudes where f l i g h t s were made, i s sym- m e t r i c a l i n the Northern and Southern Hemispheres when centered dipole coordinates are used f o r geomagnetic l a t i t u d e . d. The l a t i t u d e of the "knee" i s found to depend on depth i n the atmosphere. With the data from these f l i g h t s , one can determine the p o s i t i o n of the "knee" vs. l a t i t u d e at pressures ranging from 10 to 300 g/cm"2. e. From the large number of f l i g h t s made at various l a t i t u d e s , i t i s possible to o b t a i n a somewhat b e t t e r spectrum of the primaries than has been possible heretofore. This derived spectrum i s applicable to t h i s p a r t i c u l a r phase of the solar cycle. f. This large number of f l i g h t s also permits a study of the way i n which primar- ies of c e r t a i n rather w e l l defined magnetic r i g i d i t i e s are absorbed i n the atmosphere. g. A sudden increase i n r a d i a t i o n was found on October 16, 1958 at Bismarck. This occurred at about 60,000 f t . and lasted f o r about 15 minutes. No obvious cor- r e l a t i o n could be found w i t h a solar event. No such increase was found at Invercar- g i l l . New Zealand where an instrument was flown at the same time. There i s a possi- b i l i t y t hat t h i s increase was due to a nuclear explosion set o f f i n the region of Asia sometime previous to t h i s f l i g h t . The c o r r e l a t i o n of these data i s e x c e l l e n t , and a very good a n t i - c o r r e l a t i o n I S found w i t h Zurich sunspot numbers, thus s u b s t a n t i a t i n g the r e l a t i o n found by Forbush m 1953. 6. Bibliography. a. Papers Presented at Meetings. "The Latitude E f f e c t of Cosmic Rays at High A l t i t u d e s from Geomagnetic 87°N to 80°S." Presented at the A n t a r c t i c Symposium of Buenos Aires, 1959. "The Knee of the L a t i t u d e Curve at Balloon A l t i t u d e s . " Presented at the I n t e r n a t i o n a l Union of Pure and Applied Physics i n Moscow, 1959. "Two Unusual Events at High A l t i t u d e s . " Presented at the I n t e r n a t i o n a l Union of Pure and Applied Physics i n Moscow, 1959. b. Published Papers. H.V. Neher, Hugh Anderson: "Cosmic-Ray Changes from 1954 to 1957." Phys. Rev.. v o l . 109, no. 2, Jan. 15, 1958, p. 608. H.V. Neher: "Change of Cosmic Rays i n Space." Nature. v o l . 184, Aug. 8, 1959, pp. 423-25. H.R. Anderson: "Sudden Increase of Cosmic-Ray I n t e n s i t y . " Phys. Rev, v o l . 116, no. 2, Oct. 15, 1959, pp. 461-462. 69
COSMIC RAYS Project 2.5 - A i r Shower Detector 1. Obiectives. This p r o j e c t at the U n i v e r s i t y of C a l i f o r n i a , Santa Barbara, was designed to detect showers from high energy cosmic-ray primaries i n the energy range 10 to lO-*-Ì ev, by means of a wide-spaced counter network i n coincident arrangement. 2. Operations. Six counter s t a t i o n s were constructed and i n s t a l l e d on the campus, located at Goleta, near Santa Barbara. The s t a t i o n s were located i n an array sur- rounding a c e n t r a l s t a t i o n , and each about 400 meters away. Two 75 1. l i q u i d Cerenkov counters, i n coincident c i r c u i t r y , comprised each s t a t i o n . Pulses from each s t a t i o n were relayed by a UHF l i n k to the c e n t r a l counter and recording s t a t i o n , where coin- cident pulses were recorded from two or more of the counter s t a t i o n s . The informa- t i o n was recorded i n such a way as to i n d i c a t e the coincidence p a t t e r n between s t a t i o n s . 3. Personnel. The p r o j e c t was d i r e c t e d and c a r r i e d out by Paul H. B a r r e t t , w i t h the assistance of students i n the physics department. 4. Data. Data were reduced i n q u a r t e r l y periods and submitted to the IGY World Data Centers. 5. Results. The analysis of the data from t h i s experiment c o l l e c t e d over 44 months (August 1958 through March 1961) ind i c a t e d that the cosmic r a d i a t i o n i n the energy range 10^ to 10^^ ev does not have a d i u r n a l v a r i a t i o n larger than 8%. 6. Bibliography. a. Papers Presented at Meetings. P.H. B a r r e t t : "Measurement w i t h a Large Extensive A i r Shower Detector." Am. Phys. Soc. Meeting, Washington, D.C, May 1959. 70
COSMIC RAYS Project 2.6 - Ground Monitor Stations 1. Obiectives. This p r o j e c t was organized at the U n i v e r s i t y of C a l i f o r n i a , Berkeley, as part of a larger program to e s t a b l i s h a network of neutron monitor and meson t e l e - scope st a t i o n s to monitor time v a r i a t i o n s of the hard and s o f t cosmic-ray components. Three sets of apparatus were provided f o r i n s t a l l a t i o n i n Hawaii, C a l i f o r n i a , and An t a r c t i c a . 2. Operations. Sets of equipment were constructed, f o l l o w i n g the Chicago design f o r the neutron monitor. The i n s t a l l a t i o n i n C a l i f o r n i a was made at a research s t a t i o n near the campus at Berkeley. I n s t a l l a t i o n at Hawaii was at Makapuu Point, Oahu, a s i t e selected by the U n i v e r s i t y of Hawaii group which i n s t a l l e d a solar p a t r o l sta- t i o n . Operation of the equipment there was under a cooperative arrangement w i t h the Hawaii group. A t h i r d set of equipment was sent to Ellswo r t h S t a t i o n , A n t a r c t i c a , i n October 1958, and operated there as part of the U.S. a n t a r c t i c program. Occasional radio reports were received from E l l s w o r t h , but the o r i g i n a l records were considerably de- layed due to the f a c t that ice conditions prevented re-supply i n 1959. The equipment has been re-furbished, however, and i s now being operated by Argentine s c i e n t i s t s w i t h whom the U.S. has concluded a cooperative agreement for continuing research i n An t a r c t i c a . 3. Personnel. The p r o j e c t was organized under the d i r e c t i o n of R.B. Erode. W.B. F r e t t e r assumed r e s p o n s i b i l i t y f o r the l a t e r phase of the work when Dr. Brode was away serving as Associate D i r e c t o r of the National Science Foundation. 4. Data. Counts were recorded, by a p r i n t - o u t mechanism, at 15-minute and also at two-hour i n t e r v a l s . A camera was arranged to photograph the r e g i s t e r s and barometric equipment every minute, as backup and f o r d e t a i l e d information should a special cos- mic ray event occur. Data were corrected f o r atmospheric e f f e c t s and submitted to the IGY World Data Centers. 5. Results. A number of important f l u c t u a t i o n s , apparently associated w i t h solar f l a r e s and magnetic storms, were recorded w i t h the neutron monitor. Good c o r r e l a t i o n was found between the f l u c t u a t i o n as recorded at Berkeley and Makapuu Point, w i t h the f l u c t u a t i o n at Berkeley greater owing to the more n o r t h e r l y geomagnetic l a t i t u d e . 6. Bibliography. R.B. Brode, R.R. Brown, Dept. of Physics, Univ. of C a l i f o r n i a , Berkeley, C a l i f o r n i a and W.R. Steiger, Dept. of Physics, Univ. of Hawaii, Honolulu, Hawaii: "Solar Flare Cosmic-Ray Increase of May 4, 1960," ( I n Press). H. T r e f a l l : "Analysis of Neutron Monitor Data." 71
COSMIC RAYS Project 2.7 - Shipboard Neutron Monitor 1. Ob.iectives. This p r o j e c t at the Enrico Fenni I n s t i t u t e f o r Nuclear Studies, Uni- v e r s i t y of Chicago, was organized to obtain neutron monitor observations of cosmic-ray i n t e n s i t y i n the Southern Hemisphere. 2. Operations. An instrument was provided through the cooperation of D.C. Rose, Na- t i o n a l Research Council of Canada. I t was i n s t a l l e d on the U.S. Navy icebreaker ATKA for the 1954-55 exploratory cruise to the A n t a r c t i c . Thereafter, i n 1955-56, 1956-57 and 1957-58 i t operated onboard the ARNEB. Observations were obtained during the cruises to and from A n t a r c t i c a . The February 23, 1956 event was recorded while the ARNEB was i n port at Wellington, New Zealand. 3. Personnel. The pr o j e c t was supervised by J.A. Simpson. 4. Data. Part of the data from the cruises i s published i n the paper c i t e d i n sec- t i o n 6 below. 5. Results. The fortunate l o c a t i o n of the ARNEB on February 23, 1956, resulted i n important information on that cosmic-ray event. The monitors at Chicago and on the ARNEB yielded precise information on the time of onset, r a t e of r i s e , maximum i n t e n - s i t y and the ra t e of decline of the temporary increase, and contributed to the f u l l d e s c r i p t i o n of that unusual event. The ro u t i n e monitoring operation gave important data i n connection w i t h the study of the l o c a t i o n of the cosmic-ray equator, a program that also involved a i r c r a f t f l i g h t s i n cooperation w i t h the Geophysics Research D i r e c t o r a t e , AFCRC. 6. Bibliography. J.A. Simpson, K.B. Fenton, J. Katzman, D.C. Rose: " E f f e c t i v e Geomagnetic Equator f o r Cosmic Radiation." Phys. Rev., v o l . 102, no. 6, June 15, 1956, pp. 1648-53. P Meyer, E.N. Parker, J.A. Simpson: "Solar Cosmic Rays of February 1956 and Their Propagation through I n t e r p l a n e t a r y Space." Phys. Rev.. v o l . 104, no. 3, Nov. 1, 1956, pp. 768-83. 72
COSMIC RAYS Project 2.8 - Measurements of Primary Cosmic Radiation 1. Ob.iectives. This p r o j e c t at the Enrico Fermi I n s t i t u t e f o r Nuclear Studies, Uni- v e r s i t y of Chicago, was planned to give information on the behavior of the d i f f e r e n t components (protons, a l p h a - p a r t i c l e s ) of the primary p a r t i c l e f l u x . The emphasis i n t h i s experiment was to i n v e s t i g a t e the time v a r i a t i o n of the primary a l p h a - p a r t i c l e s and protons independently and to f i n d out how clos e l y the two components are corre- late d . I t was hoped that t h i s approach might shed l i g h t on the problem of the o r i g i n of cosmic r a d i a t i o n , p a r t i c u l a r l y i f a solar cosmic ray event were to occur, and might reveal new information on the mechanisms th a t are responsible f o r the various types of f l u c t u a t i o n s observed i n the cosmic ray i n t e n s i t y . Instrumentation was also provided to detect x - r a d i a t i o n and a li g h t w e i g h t Geiger counter assembly provided a measure of the t o t a l i n t e n s i t y . 2. Operations. I n the o r i g i n a l planning, Brownwood, Texas, and Prince A l b e r t , Sas- katchewan, Canada, were selected as the launching s i t e s f o r large balloons. These were selected not only to give wide spacing m geomagnetic l a t i t u d e , but also i n view of the surrounding t e r r a i n f o r recovery of payloads. Direct communication was es- tablished to AGIWARN (IGY World Warning Agency at Fort B e l v o i r , V i r g i n i a ) and to head- quarters at Chicago, so as to plan the balloon launching f o r periods of i n t e r e s t . Development of li g h t w e i g h t assemblies (under ten pounds) and suit a b l e balloons made i t also possible to launch equipment from Chicago simultaneously w i t h the heavy payloads. From ea r l y r e s u l t s , i t was decided that the northern f l i g h t s should remain a l o f t f o r as long as 20 hours. This increased problems connected w i t h recovery and made neces- sary the s e l e c t i o n of a new s i t e . Neepawa, Manitoba, Canada, was su b s t i t u t e d f o r Prince A l b e r t f o r the second series of f l i g h t s , i n 1958. On most f l i g h t s , h itchhike emulsion packs f o r other i n v e s t i g a t o r s were flown. The proton/alpha equipment (see Fig. 2) consisted of a three-counter v e r t i c a l t e l - escope. Counters 1 and 3 were p l a s t i c s c i n t i l l a t o r s and counter 2 was a Cerenkov de- t e c t o r . D i s c r i m i n a t i o n i n the coincidence c i r c u i t was set, using sea-level mu-mesons, so as to insure acceptance of singly-charged r e l a t i v i s t i c p a r t i c l e s . Coincidence was required between counters 1 and 3, once t h i s occurred, the pulses from counters 1 and 2 were displayed on oscilloscope tubes and photographed, along w i t h a pressure i n d i - cator and a clock. For the 1958 f l i g h t s , a dual Geiger counter u n i t was constructed, to be flown i n the large gondola. Each u n i t consisted of a p a i r of counters w i t h t h e i r l o n g i t u d i n a l axes perpendicular and i n the h o r i z o n t a l plane to minimize azimuthal v a r i a t i o n . One of the u n i t s was covered by a copper s h i e l d one-sixteenth of an inch t h i c k . This d i d not influence the c o s m i c - r a y counting r a t e but d i d allow d i f f e r e n t response to sof t rays. The two otherwise i d e n t i c a l sets of counters made i t possible t o exclude i n - strumental f l u c t u a t i o n s and since each had a high count (80 c.p.s.) at a l t i t u d e , a s t a t i s t i c a l accuracy of 1% was a t t a i n e d f o r each two minute reading. Thus, i t was possible to search f o r small i n t e n s i t y increases that might accompany solar f l a r e s . The l i g h t payload equipment consisted of a tr i p l e - c o i n c i d e n c e v e r t i c a l - c o u n t e r telescope, a single-counter omnidirectional detector, and a stack of photographic emulsions f o r the determination of a l p h a - p a r t i c l e and heavy-nuclei i n t e n s i t y . A s i x - channel tape recorder was used t o record pulse data, pressure and time. A pre-set release mechanism disconnected the balloon from the gondola and parachute. The completion of t h i s p r o j e c t was made possible by the services rendered by Raven I n d u s t r i e s , as the balloon contractor, and through support of r e l a t e d work by the A i r Force Office of S c i e n t i f i c Research and the O f f i c e of Naval Research. Dr. D.C. Rose of Canada made the arrangements without which the balloon expeditions to Prince A l b e r t 73
COSMIC RAYS ! L - 4 H H 3 ^ Counter 1 X " 4 -Counter 2 Counter 3 Scale Figure 2. Proton/Alpha Counter Equipment 74
COSMIC RAYS and Neepawa could not have been made. I n 1957, nine f l i g h t s were c a r r i e d out w i t h the al p h a - p a r t i c l e equipment, three i n Brownwood, Texas, between A p r i l 29 and June 6, and S I X i n Prince A l b e r t , Sask., between August 16 and September 16. I n 1958 s i x f l i g h t s were made from Neepawa, Manitoba, between June 13 and July 21. On many f l i g h t s , h i t c h - hike emulsion packs were flown f o r other i n v e s t i g a t o r s . 3. Personnel. This work was Under the supervision of J.A. Simpson. P r i n c i p a l i n - v e s t i g a t o r s carrying out the balloon program were Peter Meyer and K.B. Fenton. 4. Data. The proton/alpha equipment, described above, produced cathode ray displays of pulses, which were photographed. These photographs were projected on a c a l i b r a t e d screen and the data punched onto IBM cards. I t took approximately three weeks time of an experienced operator to punch data from eight hours of f l i g h t . Data from 1957 f l i g h t s have been sent to the ICY World Data Center, the remaining data are being an- alyzed and prepared f o r submission. 5. Results. The 1957 f l i g h t s have been analyzed and i n t e r p r e t e d . The al p h a - p a r t i c l e f l u x was extrapolated to the top of the atmosphere and the proton f l u x evaluated f o r a l e v e l under 13.5 gram/cm" of res i d u a l atmosphere. The percentage change i n proton f l u x (averaged over the time at a l t i t u d e ) was very clo s e l y the same as th a t deduced from neutron monitor data at Climax. The observation that the i n t e n s i t y changes at a l t i t u d e over Prince A l b e r t are not s u b s t a n t i a l l y larger than at Climax r e f l e c t s the fa c t that the low energy c u t - o f f f o r primary p a r t i c l e s at the time of the expedition I S close to the magnetic c u t - o f f f o r Climax, and that few a d d i t i o n a l low energy p r i - mary protons are observed at the l a t i t u d e of Prince A l b e r t that do not also con t r i b u t e to the Climax i n t e n s i t y . The a l p h a - p a r t i c l e i n t e n s i t y , w i t h i n the s t a t i s t i c a l e r r o r of the measurement, ex h i b i t e d a s i m i l a r v a r i a t i o n . The r e s u l t i s not incompatible, therefore, w i t h the assumption of a common modulating mechanism operating simultan- eously on the proton and alpha components. I n order to study possible short term f l u c t u a t i o n s i n the al p h a - p a r t i c l e f l u x , the data of each f l i g h t were divided i n t o several short i n t e r v a l s , each l a s t i n g f o r about 90 minutes. I n each case the proton f l u x followed i n a rough way the neutron monitor i n t e n s i t y as recorded i n Climax, Colorado. I n a d d i t i o n to the main equipment, a small Geiger counter telescope was c a r r i e d on those f l i g h t s ( i d e n t i c a l w i t h the l i g h t pay- load described above) which independently recorded the t o t a l cosmic-ray i n t e n s i t y . This provided an independent check on the proton i n t e n s i t y measurement and a very good c o r r e l a t i o n was found between the Geiger counter i n t e n s i t y data and the proton f l u x . The a l p h a - p a r t i c l e f l u x , on the other hand, exhi b i t e d some unexpected and indepen- dent v a r i a t i o n s . This was most c l e a r l y seen i n the f l i g h t on September 15, 1957. During the e n t i r e time of the f l i g h t the al p h a - p a r t i c l e i n t e n s i t y increased, u n t i l , at the end of the f l i g h t , i t reached a value about 40% above the i n i t i a l f l u x . A s i m i l a r behavior i n the al p h a - p a r t i c l e f l u x i s noticed i n other f l i g h t s . At the present time these observations are i n t e r p r e t e d as being due to an aniso- tropy i n the al p h a - p a r t i c l e f l u x which would e x h i b i t i t s e l f as a 24-hour v a r i a t i o n i n alp h a - p a r t i c l e i n t e n s i t y . Such a v a r i a t i o n cannot be the r e s u l t of any one of the modulating mechanisms th a t were put forward i n the past years to describe the i n t e n s i - t y v a r i a t i o n s i n cosmic r a d i a t i o n . I t was decided that a more d e t a i l e d i n v e s t i g a t i o n of t h i s e f f e c t was necessary and important and t h a t , i n p a r t i c u l a r , the time the equipment spends at a l t i t u d e had to be s u b s t a n t i a l l y increased. This was the reason that led, i n 1958, to a concentration on f l i g h t s that stayed at a l t i t u d e f o r approximately 20 hours. I n 1958 a series of f l i g h t s was made at Neepawa, where balloons stayed at a l t i t u d e some 20 hours. 75
COSMIC RAYS On some f l i g h t s i n 1957, a dual neutron monitor was flown on separate f l i g h t s to search f o r i n t e n s i t y increases accompanying small solar f l a r e s and to study non-sta- t i s t i c a l cosmic-ray i n t e n s i t y f l u c t u a t i o n s occurring m short i n t e r v a l s 6. Bibliography. a. Papers Presented at Meetings. Peter Meyer* "Changes of the Primary Alpha-Particle Flux of Cosmic Radiation During High Solar A c t i v i t y . " American Physical Society, Washington, May 1958. Peter Meyer: "Recent Experiments on the Primary Alpha P a r t i c l e s of Cosmic Rays," American Physical Society, November 1958. Peter Meyer. "Cosmic Ray Protons and Alpha P a r t i c l e s from the Sun." American Physical Society, Pasadena, December 1959. b. Published Papers. Peter Meyer "Primary Cosmic Ray Proton and Alpha P a r t i c l e I n t e n s i t i e s and Their V a r i a t i o n w i t h Time." Physical Review, v o l . 115, 1959, pp. 1734-41. Peter Meyer: "The Cosmic Ray Alpha P a r t i c l e Flux During Sharp Forbush I n - t e n s i t y Decreases." JGR, v o l . 65, 1960, p. 3881. 76
COSMIC RAYS Project 2.9 - Mu-Meson Monitor m the A n t a r c t i c 1. Objectives. A meson telescope to monitor cosmic-ray i n t e n s i t y was constructed at the Department of Physics, U n i v e r s i t y of Maryland, f o r i n s t a l l a t i o n at Wilkes S t a t i o n , A n t a r c t i c a . This was part of a program, f o l l o w i n g CSAGI recommendations, to monitor the cosmic-ray i n t e n s i t y over a wide range of geomagnetic l a t i t u d e . 2. Operations. A standard lUPAP design t r i p l e - c o i n c i d e n c e cubical telescope was con- structed and i n s t a l l e d at Wilkes. Data p r i n t e r s recorded b i - h o u r l y values f o r the e n t i r e telescope and another recorder was provided f o r fifteen-mmute readings o f each half-telescope ( h a l f of each t r a y ) . The instrument was l a t e r modified to provide also the double-coincidence counting ra t e f o r the upper two tra y s . 3. Personnel. This work was c a r r i e d out under the supervision of S.F. Singer and Mart i n Swetnick. 4. Data. Data have been processed and submitted to the IGY World Data Center. 5. Results. Data have been analyzed under Project 2.32 w i t h special emphasis on seasonal and d a i l y v a r i a t i o n s . Project 2.10 - Mu-Meson Monitor at Thule 1. Objectives. A meson telescope to monitor cosmic-ray i n t e n s i t y was constructed at the Department of Physics, U n i v e r s i t y of Maryland, f o r i n s t a l l a t i o n at Thule, Green- land. This was part of a program, f o l l o w i n g CSAGI recommendations, to monitor the cosmic-ray i n t e n s i t y over a wide range of geomagnetic l a t i t u d e . 2. Operations. A standard lUPAP design t r i p l e - c o i n c i d e n c e cubical telescope was constructed and i n s t a l l e d at Thule. Data p r i n t e r s recorded b i - h o u r l y values f o r the e n t i r e telescope and another recorder was provided f o r fifteen-mmute readings of each half-telescope ( h a l f of each t r a y ) . The instrument was l a t e r modified to pro- vide also the double-coincidence counting rate f o r the upper two trays. 3. Personnel. This p r o j e c t was c a r r i e d out under the supervision of S.F. Singer and Martin Swetnick and W.R. Webber. 4. Data. Data have been processed and submitted to the IGY World Data Center. 5. Results. Data have been analyzed under Project 2.32. I n e a r l y 1958, several un- usual events were observed, when the double coincidence c i r c u i t of the top and middle trays showed unique f l u c t u a t i o n s . The i n t e n s i t y decreased abruptly, remained at the new value f o r several minutes to tens of minutes and then abruptly returned to i t s o r i g i n a l value. I n c e r t a i n instances the i n t e n s i t y f l u c t u a t i o n s appeared to have an o s c i l l a t o r y f l u c t u a t i o n about a mean w i t h periods of about f i v e minutes. 77
COSMIC RAYS Project 2.11 - Study of High Speed Cosmic-Ray Fluctuations 1. Objectives. This p r o j e c t at the U n i v e r s i t y of Maryland was concerned w i t h the establishment and operation of high counting r a t e meson detectors at mountain s t a t i o n s . The purpose was to study i n t e n s i t y v a r i a t i o n s i n the primary r a d i a t i o n of 1 per cent or greater occurring w i t h i n a time i n t e r v a l ranging from a few seconds to several min- utes, presumably associated w i t h solar f l a r e s . 2. Operations. As a consequence of the desire to study small v a r i a t i o n s , i t was r e - quired that the t o t a l instrumental e r r o r , i n c l u d i n g s t a t i s t i c a l f l u c t u a t i o n s , be no greater than 1 per cent over a period of approximately 10 seconds. This requires a counting rate of at least 1000 events per second. With the l o c a t i o n of the mountain s t a t i o n s at Climax (11,000 f t . ) , Colorado, and Banff (8,000 f t . ) , Canada, t h i s , i n t u r n , required an e f f e c t i v e counting area of approximately 4m^. To o b t a i n such an area 10 trays of area 30 x 45 inches were used at each l o c a t i o n . Each t r a y consisted of 30 halogen f i l l e d counters. The trays were placed one above the other, thus pro- ducing 5 coincidence telescopes of area nearly 1 m each. The outputs of a l l 5 c o i n - cidence elements were placed i n t o a common i n t e g r a t i n g r a t e meter whose output was fed i n t o a Sanborn recorder which i n i t i a l l y moved at the r a t e of 30"/hr., i n September 1958. This was l a t e r reduced to 5"/hr., and f i n a l l y to l - l / 2 " / h r . , i n September 1958. The complete equipment was constructed i n the laboratory at the U n i v e r s i t y of Maryland. Real f l u c t u a t i o n s have been observed on an airplane f l i g h t (Singer, Swetnick, Phys. Rev.. L e t t e r s . 1958). I t i s f e l t that s i m i l a r v a r i a t i o n s w i l l occur at moun- t a i n s t a t i o n s and therefore the experimental program and data analysis should continue. 3. Data. Data are being reduced at the U n i v e r s i t y of Maryland, but there are no plans f o r p u b l i c a t i o n as yet. As t h i s was a special experiment, data were not reduced i n standard form and submitted to the data centers. 4. Results. Data have been analyzed under Project 2.32. The period of IGY was mostly spent improving the apparatus and e l i m i n a t i n g instrumental problems. The major r e s u l t was the establishment of two mountain s t a t i o n s which are continuing i n operation under support from other agencies. 78
COSMIC RAYS Project 2.12 - Cosmic-Ray I n t e n s i t y at High A l t i t u d e 1. Objectives. This p r o j e c t , at the School of Physics, U n i v e r s i t y of Minnesota, was planned to monitor as continuously as possible the cosmic ray i n t e n s i t y near the top of the atmosphere at Minneapolis. Some r e l a t e d balloon f l i g h t s were also made at other lo c a t i o n s . 2. Operations. A series of e i g h t y - f i v e f l i g h t s were made w i t h large constant l e v e l polyethylene "skyhook" balloons, which a t t a i n e d a l t i t u d e s of about 30 km (10 mb) i n about a two-hour r i s e time. The balloons then l e v e l l e d o f f and remained at a l t i t u d e f o r times up to twenty hours. Most of the f l i g h t s were launched from Minneapolis, but a few f l i g h t s were made from other locations (Sioux F a l l s , S.D., Crosby, Minn., South St. Paul, Mmn., Huron, S.D.; Brownwood, Texas; Guantanamo, Cuba, Guam, Moberly, Mo.; and Fairbanks, Alaska). The equipment flown included a spherical i n t e g r a t i n g i o n i z a t i o n chamber, Geiger counter, a recording package containing a small a e r i a l camera and a pressure trans- ducer, telemetering t r a n s m i t t e r , and nuclear emulsions. The equipment was se n s i t i v e to primary cosmic rays and t h e i r time v a r i a t i o n s , X rays and gamma rays, and radia- t i o n s from ra d i o a c t i v e debris i n the atmosphere. 3. Personnel. The p r o j e c t was under the supervision of E.P. Ney and J.R. Winckler; other key personnel were R. Arnoldy, R. Hoffman, L. Peterson, P.S. Fr e i e r . 4. Data. Normalized i o n i z a t i o n chamber rates and Geiger counter rates were tabulated f o r a l l f l i g h t s i n a data book published by the group. The data obtained during as- cent of the balloon were given i n graphical form and included also the r a t i o of ion rat e to counter r a t e as a fu n c t i o n of balloon pressure height. The data obtained at c e i l i n g a l t i t u d e were given i n tabular form averaged over f i f t e e n minute i n t e r v a l s , geographic coordinates, obtained p a r t l y from radio t h e o d o l i t e observations, but mainly from a e r i a l camera photographs, are Included i n the constant l e v e l p o r t i o n of the data. These data books were d i s t r i b u t e d to cosmic ray workers and also to the IGY World Data Centers. 5. Results. A large number of analyses of the data produced a wealth of information, some of I t unexpected; i t i s possible here to summarize only b r i e f l y the r e s u l t s . a. High A l t i t u d e I o n i z a t i o n Rate. The data are summarized i n Fig. 3 where neu- t r o n monitor data from the Deep River s t a t i o n are included through the courtesy of Dr. Hugh Carmichael of Canada and data of H.V. Neher are p l o t t e d f o r comparison; Neher's data from Thule were normalized together w i t h Minneapolis data. This proce- dure I S j u s t i f i e d on the basis t h a t there was no l a t i t u d e e f f e c t between these two points i n 1937. One s t r i k i n g feature o f t h i s data summary i s the large decrease i n i n t e n s i t y accompanying the solar maximum period. Another feature i s the many large sudden i n t e n s i t y decreases which show i n a l l instruments, although i t must be noted that the monitoring at the top of the atmosphere i s much coarser than the continuous ground l e v e l monitoring. An examination of solar data shows that a l l of the large Forbush decreases observed were associated w i t h intense solar f l a r e s that occurred one to two days p r i o r to the decrease. Because many of the f l i g h t s remained at a nearly constant l e v e l f o r almost a day, i t was possible to look f o r d i u r n a l e f f e c t s . Under normal conditions, i t i s f e l t that there were no d i u r n a l e f f e c t s w i t h an upper l i m i t of the order of about two percent i n the t o t a l i o n i z a t i o n or Geiger r a t e . However, on one occasion, at l e a s t , a strong d i u r n a l e f f e c t was observed occurring during a geomagnetic disturbance during the low i n t e n s i t y period of a Forbush type decrease. This e f f e c t has been observed 79
COSMIC RAYS 35r WEAK STRONG 11 I i i n TYPE m SEA LEVEL NEUTRONS ilil.lilili ⢠I . I . I . I . I . .1.1 I . |M I I I | I . 1 1 . 1 . 1 J ' F ' M ' A ' M ' J ' J ' A ' S ' O ' N ' D -198a- » G/CM* ATMOSPHERIC DEPTH TOTAL OaZATION TOTAL ENERGY INFLUX Figure 3. Summary of IGY High A l t i t u d e Measurements Compared w i t h Sea Level Cosmic- Ray Detectors. Upper Curve; neutron monitor i n t e n s i t i e s . Chalk River; middle curve: t o t a l cosmic-ray i o n i z a t i o n a t 10 gm/cm atmospheric depth; bottom curve: t o t a l energy i n f l u x measured as i o n i z a t i o n . Data ind i c a t e d as square points ( J u l y 1955-Jan 1957) were obtained w i t h small Geiger coincidence telescopes. Data of Neher close to the geomagnetic poles and extending back to solar minimum i n 1954 ( c i r c l e s ) were normal- ized to the Minnesota data. Arrows represent times when solar-generated low-energy cosmic rays were known to be in c i d e n t over the polar region. The balloon above an arrow indicates a d i r e c t measurement of these solar cosmic rays, e i t h e r a t Minneapolis or a t high l a t i t u d e . 80
COSMIC RAYS JUNE 30.1957 ILJ SEPT I2.I9S7 SEPT 22.1957 FEE 10.1958 K) (PULSES/SEC xK)*) AUG. 16.1968 OCT 23,1958 A MARCH 27. 1959 1900 2400 0400 0800 CENTRAL STANDARD TME BOO eoo aooo Figure 4. Sunnnary of auroral X-ray bursts observed w i t h i o n i - z a tion chambers during the IGY period. The bursts are p l o t t e d as a f u n c t i o n of l o c a l time i n the c e n t r a l standard time zone a t Minneapolis. The ion chamber r a t e i s on the normalized scale w i t h t t h e cosmic ray background subtracted. Cosmic ray rates w i t h the same chamber are between 15 and 20 pulses/sec x 10^. Only the September 12th case represents the Gelger counter curve as the ion chamber was not a v a i l a b l e on t h i s f l i g h t . 81
COSMIC RAYS previously and seems to be connected w i t h an anisotropy of outer space t o the g a l a c t i c cosmic rays and i n time, w i t h proper analysis, i t may be possible t o examine the causes of the anisotropy i n terms of solar magnetic f i e l d s . Various attempts at t r e a t i n g the data to f u r t h e r knowledge of the solar cycle and Forbush modulation mechanism have been made, the discussion of which i s beyond the scope of t h i s report (see Wmckler, Technical Report No. CR-26) . b. Solar Cosmic Rays. Probably the most s i g n i f i c a n t f i n d i n g of the e n t i r e series was the frequent occurrence of intense low-energy solar cosmic rays which have been i d e n t i f i e d as mostly protons. These o r i g i n a t e d from large solar f l a r e s but had an energy spectrum so steep that the p a r t i c l e s were not detected by the extensive sea l e v e l monitoring network. The p a r t i c l e s could e a s i l y be detected at a l t i t u d e s of 20 or 25 km or greater; they showed very strong r e l a t i o n s h i p s to ionospheric e f f e c t s and were detected i n d i r e c t l y by cosmic noise recorders (see p r o j e c t 1.43). I n a l l cases m which the solar proton e f f e c t s were seen at Minneapolis, a geomagnetic storm was i n progress. I n one case when large high l a t i t u d e e f f e c t s were observed, and geo- magnetic storm a c t i v i t y was absent, no proton e f f e c t s were observed at Minneapolis. The proton events also seem c l o s e l y linked w i t h auroral occurrence. These events have shown t h a t , contrary to views held e a r l i e r , the sun i s a p r o l i f i c source of p a r t i c l e s w i t h energies j u s t high enough to be included m the cosmic-ray range. c. Analysis of Auroral Rays. The i n i t i a l discovery of X rays at balloon l e v e l s d i r e c t l y coincident w i t h v i s i b l e auroras occurred on July 1, 1957 (UT), the opening day of the IGY period. Detection devices, i n c l u d i n g shielded Geiger counters, arranged to be se n s i t i v e only to photons, and s c i n t i l l a t i o n counters were added to f l i g h t equip- ment a f t e r the i n i t i a l discovery. The observations are summarized i n Fig. 4 which i s somewhat biased as balloons are normally launched about sunset so that e a r l y a f t e r - noon a c t i v i t y would usually be missed. A l l of the bursts occurred during very large storms w i t h large magnetic f l u c t u a t i o n s , they v a r i e d enormously i n size, which i s probably an i n d i c a t i o n i n some way of the i n t e n s i t y of the solar bombardment. The c h a r a c t e r i s t i c of the time constant, however, was s i m i l a r f o r a l l cases and i s about one-half hour. The bursts showed considerable f i n e s t r u c t u r e , though w i t h v a r i a t i o n s i n the one-minute range. The f o l l o w i n g general observations could be made on the nature of these bursts' ( i ) When the skies are clear and v i s u a l observations can be made at the time of the balloon X ray bursts, i t was found that the bursts corresponded to i n - t e n s i f i c a t i o n of auroral luminosity close to the zenith at Minneapolis. This obser- v a t i o n i n e f f e c t associated the electrons producing the X rays w i t h the v i s u a l forms of the aurora. This follows because the absorption c o e f f i c i e n t f o r the observed X ray energies of 50-100 kev i s approximately 0.2 cm per gm. For example, at the nom- i n a l balloon c e i l i n g height of 10 g/cm the r a t i o of the expected i n t e n s i t y from the v e r t i c a l compared to a 60° ze n i t h angle f o r a uniform source of X rays i s 7. This implies that X rays i n general w i l l be seen only from e l e c t r o n currents i n c i d e n t close to the ze n i t h considering the nominal auroral height of 100 km. X rays w i l l be seen from electrons s t r i k i n g the atmosphere only w i t h i n a radius of about 100 km from the balloon. ( i i ) When a c a r e f u l comparison was made between the X ray bursts and au r o r a l a l l - s k y camera photographs, i t was found that the time of the burst was associated w i t h i n times of the order of one minute w i t h the passage across the zenith of regions of high luminosity. See f o r example the discussion given i n Winckler et a l (1959), Figure 3, f o r the aurora of February 10, 1958. The apparent v e l o c i t y of the luminous regions across the sky was o f t e n found to be of the order of 0.5 to 1 km per sec from the a l l - s k y camera records. This i s consistent w i t h the agreement w i t h i n one minute 82
COSMIC RAYS or so between the appearance of the luminosity and the X ray bursts considering the 100-km-radius c r i t e r i o n above f o r d e t e c t i n g the X rays. ( i l l ) The energy of the X rays that i s accessible to measurement at balloon le v e l s begins at about 40 kev and extends upwards, however, by examining the r a t i o of the instruments (Winckler et a l , 1958), the energy of the X rays at balloon levels i n many cases was estimated t o range from 50 t o 100 kev. The shape of the spectrum could be determined from the ion chamber and Geiger counter but i t was believed to be that of a bremsstrahlung spectrum of electrons s t r i k i n g a i r plus the energy-sensitive ab- sorption of the atmosphere which attenuates strongly the very low energy X rays. This i n e f f e c t produces a maximum i n the spectrum at about the energies mentioned above. From the observed sizes o f the bursts i n the i o n chamber i t was possible t o estimate the e l e c t r o n f l u x assuming th a t the f l u x i s uniform over the r e s t r i c t e d region near the zenith to which the instruments are s e n s i t i v e . The r e l a t i o n between the e l e c t r o n f l u x i n c i d e n t on the atmosphere and the normalized ion chamber rat e given m Fig. 4 i s discussed below. ( i v ) The X ray bursts studied at Minneapolis were associated w i t h sub-auroral zone auroras. This means th a t not any of the observations were associated w i t h the phenomenon c a l l e d a "quiet arc," as such phenomena are r a r e l y seen at the zenith at Minneapolis. Rather, the X rays were associated w i t h rayed forms such as rayed-arcs, rayed-bands and corona which represent a phase of the a u r o r a l storm accompanying the motion of the luminosity e i t h e r i n l a t i t u d e or i n longitude. (v) I t i s known th a t there i s a close association between the presence of magnetic bays at a given l a t i t u d e and the advance or r e t r e a t of the aurora across that l a t i t u d e . I t i s therefore understandable t h a t there was an association between the presence of the auroral X rays and the presence of bays on the magnetic records. Such an association f o r the February 10 aurora was pointed out (Winckler et a l , 1959). ( v i ) The power a v a i l a b l e i n the electrons i n f e r r e d from the X rays was very large and i s comparable w i t h the power required to produce the v i s u a l luminosity of an aurora. I t i s therefore probable that the electrons were a major c o n t r i b u t o r to the e x c i t a t i o n of the auroral spectrum as observed. ( v i i ) The observation of electrons at 100 kev energy as a d i r e c t part of the v i s u a l aurora raised an i n t e r e s t i n g question about the o r i g i n of these electrons. I t i s known that strong a u r o r a l storms are f r e q u e n t l y associated w i t h v i o l e n t solar f l a r e s occurring about one day e a r l i e r , and i n f a c t such was the case i n the storms summar- ized i n t h i s discussion. The 100-kev electrons cannot have come d i r e c t l y from the f l a r e w i t h a speed c h a r a c t e r i s t i c of t h e i r v e l o c i t y which i s about 0.9 the speed of l i g h t . This means that e i t h e r the electrons were trapped i n the plasma cloud and t r a v e l l e d around i n t h i s cloud during i t s t r a n s i t from the sun, perhaps because of magnetic f i e l d s or e l e c t r o s t a t i c forces, or the electrons were discharged from the Van A l l e n regions around the earth -- i n t h i s case they would c o n s t i t u t e part of the semi-permanent f l u x of such electrons observed i n the outer Van A l l e n region; or, f i n - a l l y , the electrons were l o c a l l y accelerated i n the earth's magnetic f i e l d at the time of incidence of the solar cloud and were discharged down the l i n e s of force as part of the auroral phenomenon. d. Measurement of Solar Gamma-Rays and Radioactive Layers i n the Atmosphere. A t r a n s i t o r y increase i n an i n t e r v a l of only 18 seconds was observed i n the ion chamber and counter on F l i g h t IGY-M on 20 March 1958, flown over the i s l a n d of Cuba. The increases were s i g n i f i c a n t l y above the low and rather steady background of the cosmic r a d i a t i o n at the l a t i t u d e of Cuba. I t was found that the increase coincided p r e c i s e l y w i t h a very intense radio burst observed on 3 cm and on 21 cm by the radio astronomy group at Meudon. The increase also coincided w i t h the maximum phase of a class I I f l a r e . The event has been analyzed i n i t s e n t i r e t y (Peterson and Winckler, 1959) as being due to a burst of high energy X rays or gamma rays coming frran the sun and prob- ably generated there by electrons accelerated i n the f l a r e and producing bremsstrah- lung i n the photosphere of the sun. I t was concluded that 9.4 x 10^^ electrons 83
COSMIC RAYS producing the bremsstrahlung on the sun were required to account f o r the observed burst. I f one estimates the number of electrons required to produce synchrotron r a d i a t i o n , as- suming that the radio observation i s due to t h i s source, the number of electrons of s i m i l a r energy i s 2.5 x 10 . This discrepancy of 10 i s not d i f f i c u l t t o expl a i n i n terms of the opacity of the solar photosphere to the electromagnetic r a d i a t i o n . The event i s s e l f - c o n s i s t e n t w i t h the above i n t e r p r e t a t i o n but has one very puzzling fea- t u r e , namely that the source of the radio waves observed at Meudon was observed to be very large. The size was such that the e f f e c t s would have to have spread across the solar disc w i t h the v e l o c i t y of l i g h t and produce the electromagnetic r a d i a t i o n i n the radio frequency spectrum from the whole region (about one-third the size of the solar disc) simultaneously. I t appears that t h i s observation of gamma rays from outside the earth i s the only observation so f a r recorded of such a phenomenon. No other observa- t i o n of solar gamma rays was made during the IGY period although a number of balloon f l i g h t s were at high a l t i t u d e during strong solar f l a r e s . I n cases where increases were observed associated w i t h f l a r e s , i t was shown that these were due to p a r t i c l e e f f e c t s or were otherwise accounted f o r . On balloon F l i g h t IGY-27 on the 21st of March 1958 an increase was observed m both the i o n chamber and the counter while the balloon was r i s i n g through the lower atmosphere at a pressure of about 350 mb. The increases were almost c e r t a i n l y due to a strong r a d i a t i o n layer i n the atmosphere. Another case t e n t a t i v e l y assigned to a radi o a c t i v e cloud layer was observed on F l i g h t IGY-54, on the 31st of October 1958, A d e t a i l e d study has been made of these two events (Mantis and Winckler, 1960). I t was concluded that on the 21st of March 1958 event the increases i n the instruments were due to gamma rays of approximately 1 Mev i n energy and having a s p e c i f i c a c t i v i t y of 0.8 X 10"^ d i s i n t e g r a t i o n s per second per cm of a i r at 30,000 f e e t . The layer containing the a c t i v i t y was located i n the j e t stream and the t r a j e c t o r y could be f o l - lowed backwards w i t h a time delay of about f i v e days to a probable source i n S i b e r i a . I n analyzing the event, the decay of the f i s s i o n fragments and the loss of i n t e n s i t y by d i f f u s i o n was estimated. I t should be noted that the r a d i o a c t i v e layer was not observed on the descent of e i t h e r of the balloons, although t h i s descent occurred only a few hundred miles from the launch p o i n t . There was no other case i n the 83 IGY b a l - loon f l i g h t s on t h i s program intense enough to be detected. The d i r e c t d e t e c t i o n of rad i o a c t i v e debris i n s i t u i n the atmosphere i s unusual. The f a c t that i t i s possible to make such measurements suggests that w i t h more se n s i t i v e techniques the d i r e c t sounding measurement of the r a d i o a c t i v i t y might be a useful t o o l f o r studying the d i s - t r i b u t i o n of ra d i o a c t i v e m a t e r i a l and drawing inferences concerning the large scale c i r c u l a t i o n of the atmosphere. 6. Bibliography. a. Papers Presented at Meetings. These experiments were reported at a v a r i e t y of AGU, APS and special meetings i n the period 1958-1960. b. Published Papers. J.R. Winckler and K.A. Anderson: "High A l t i t u d e Cosmic-Ray La t i t u d e E f f e c t from 51° to 65° N Geomagnetic L a t i t u d e . " Phys. Rev., v o l . 108, 1957, pp. 148-154. J.R. Winckler and L. Peterson: "A Large Cosmic-Ray Decrease Accompanying the Solar Maximum of 1957." Nature, v o l . 181, 1958, pp. 1317-1321. J.R. Winckler, L. Peterson, R. Arnoldy, and R. Hoffman: "X Rays from V i s i b l e Aurorae at Minneapolis." Phys. Rev., v o l . 110, 1958, pp. 1221-1231. 84
COSMIC RAYS E.P. Ney and J.R. Winckler. "High A l t i t u d e Cosmic-Ray Measurements During the IGY." Geophysical Monograph No. 2, pp. 81-91, Amer. Geophys. Union, Washington, D. C, 1958. P. Fowler, P.S. Fr e i e r , and E.P. Ney: "The Primary Alpha P a r t i c l e Spectrum Over North America and Geomagnetic Cutoff Energies." Nuovo Cimento. Supp. to Vol. 8. Serie X, 1958, pp. 492-499. P.S. F r e i e r , E.P. Ney, and C.J. Waddington: "Lithium, Beryllium, and Boron i n the Primary Cosmic Radiation." Phys. Rev., v o l . 113, 1959b, pp. 921-927. E.P. Ney, J.R. Winckler, and P.S. Freier: "Protons from the Sun on May 12, 1959." Phys. Rev. L e t t e r s , v o l . 3, 1959, pp. 183-185. J.R. Winckler, L. Peterson, R. Hoffman, and R. Arnoldy: "Auroral X Rays, Cosmic Rays, and Related Phenomena During the Storm of February 10-11, 1958." JGR. v o l . 64, 1959, pp. 597-610. P.S. F r e i e r , E.P. Ney, and J.R. Winckler: "Balloon Observation of Solar Cos- mic Rays on March 26, 1958." JGR, v o l . 64, 1959, pp. 685-688. L.E. Peterson and J.R. Winckler: "Gamma-Ray Burst from a Solar Flare." JGR. v o l . 64, 1959, pp. 697-708. K.A. Anderson, R. Arnoldy, R. Hoffman, L. Peterson and J.R. Winckler: "Obser- vations of Low Energy Solar Cosmic Rays from the Flare of 22 August 1958." JGR, v o l . 64, 1959, pp. 1133-1147. P.S. Fr e i e r , E.P. Ney, and C.J. Waddington: "Flux and Energy Spectrum of Cosmic-Ray a-Particles During Solar Maximum." Phys. Rev., v o l . 114, 1959a, pp. 365-373. H.T. Mantis: "Winds and Wind Structure at 100,000 Feet from Constant A l t i t u d e Balloon T r a j e c t o r i e s . " Tech. Rept. AF-15. Atmospheric Physics, Univ. of Minnesota, Minneapolis, 1959. R.A. Hoffman- "Standardization of I o n i z a t i o n Chambers." Tech. Rept. CR-27. Cosmic Ray Group, School of Physics, Univ. of Minnesota, Minneapolis, 1960. J.R. Winckler- "Balloon Study of High A l t i t u d e Radiations during the IGY", v o l . 65, pp. 1331-60, May 1960. H.T. Mantis and J.R. Winckler: "Balloon Observation of A r t i f i c i a l Radio- a c t i v i t y at the Base of Stratosphere." JGR. v o l . 65, pp. 3515-20, November 1960. J.R. Winckler, P.D. Bhausar, L. Peterson: "The Time Vari a t i o n s of Solar Cos- mic Rays during July 1959 at Minneapolis," JGR, v o l . 66, pp. 995-1022, A p r i l 1961. 85
COSMIC RAYS Project 2.13 - Low Energy Heavy Primary Cosmic Rays 1. Objectives. This p r o j e c t of Dr. Herman Yagoda, National I n s t i t u t e s of Health, provided f o r the scanning and measurement of nuclear emulsion plates flown to high a l t i t u d e s on rockets. The purpose was to i n v e s t i g a t e the f l u x of low energy heavy primaries to obtain the charge and energy spectrum as w e l l as to evaluate the health hazards to persons f l y i n g near the top of the atmosphere. 2. Operations. Five Aerobee rockets were launched by the AFCRL from Holloman A i r Force Base, New Mexico, i n 1957. Two recoveries, one day and one n i g h t , were made. The experimental c o n d i t i o n permitted the f l u x at the top of the atmosphere to be measured w i t h only 0.137 gm/cm" of condensed matter (aluminum) i n t e r v e n i n g . 3. Personnel. The work was supervised by Dr. Herman Yagoda. 4. Data. The r e s u l t s of the scanning of the plates have been published as GRD Geo- physical Research Paper No. 60, July 1958. 5. Results. The average f l u x f o r these f l i g h t s was 4.98 ± 0.65 (m^-sec.sterad.^-1^ about 20 percent smaller than observed from Viking rocket f l i g h t s i n 1952-54. These e a r l i e r f l i g h t s , however, had approximately 2-5 gm/cm of int e r v e n i n g condensed matter. The reduction i n f l u x i s consistent w i t h Neher's observation (see Project 2.4) that the f l u x diminished twofold between 1954 and 1957. 6. Bibliography. a. Papers Presented at Meetings. H. Yagoda: 2nd I n t . Conf. on Corpusc. Photog., Sept. 1958, Montreal. b. Published Papers. Herman Yagoda: "Observations on Heavy Primary Cosmic-Ray Nuclei Above the Atmosphere." Geophysical Research Paper No. 60, July 1958, GRD/AFCRC, Bedford, Mass. 86
COSMIC RAYS Projects 2.14, 2.15 - Atmospheric, Geomagnetic and Solar Influences on the Mu-Meson and Nucleonic Components of the Cosmic Radiation 1. Obiectives. These p r o j e c t s at the U n i v e r s i t y of Nebraska provided f o r the con- s t r u c t i o n and operation of neutron monitor and meson telescopes. These served not only to augment the i n t e r n a t i o n a l network of monitors but to provide data f o r a de- t a i l e d study of f l u c t u a t i o n s i n the sea l e v e l f l u x . 2. Operations. A neutron monitor p i l e , f o l l o w i n g the Chicago-IUPAP design, was con- str u c t e d . A graduate student v i s i t e d the Chicago laboratory of J.A. Simpson to study the i n s t a l l a t i o n there and become f a m i l i a r w i t h the c i r c u i t r y . Two meson telescopes, using the standard c u b i c a l design, were constructed. Extra counter trays above the cubical array and c i r c u i t r y were arranged to provide, i n a d d i t i o n to the cubical t e l - escopes, two narrow angle (approximately 20°) v e r t i c a l telescope and an east-west array f o r the study of assymetry i n the f l u x . The u n i t s were i n s t a l l e d i n an a i r - conditioned space, supplied by the U n i v e r s i t y , w i t h temperature c o n t r o l to w i t h i n 1°/ day d r i f t . Upper a i r data, f o r applying pressure c o r r e c t i o n s , was obtained from the USWB s t a t i o n at Omaha, a Bendix-Friez p r e c i s i o n microbarograph, c a l i b r a t e d against a mercury barometer, was used at the s t a t i o n f o r ground l e v e l information or pressure, and to check against the Omaha data. Data p r i n t e r s were used to record counts on a 15 minute basis. This p r o j e c t continued a f t e r the IGY under support from NSA. The neutron monitor was moved to the U n i v e r s i t y of Denver i n 1962. 3. Personnel. This p r o j e c t was under the supervision of R.L. Chasson, Kaichi Maeda and W.R. French, J r . were the p r i n c i p a l senior a s s i s t a n t s . 4. Data. Counts were t r a n s f e r r e d to punch cards and corrections applied. The r e - s u l t i n g reduced data were submitted to the IGY World Data Centers. 5. Results. a. Local and World-Wide Events. The i n t r o d u c t o r y world-wide studies covered ap- proximately the f i r s t year of IGY and were c a r r i e d out f o r one l a t i t u d e b e l t (50°N geomag.). The key s t a t i o n s chosen from the IGY network were Yakutsk, Weissenau, and L i n c o l n , which are p r a c t i c a l l y equally-spaced w i t h regard to geomagnetic longitude. The corrected b i h o u r l y neutron data from these s t a t i o n s were averaged together, using the quiet-day l o c a l standard deviations f o r i n t e n s i t y weighting f a c t o r s , and the log- arithmic world-wide b i h o u r l y i n t e n s i t y v a r i a t i o n s were then computed and p l o t t e d . This permitted the subsequent c a l c u l a t i o n of world-wide-minus-local differences f o r each of the c o n t r i b u t i n g s t a t i o n s . A d e t a i l e d study was then made of the i n t e n s i t y trends f o r these three sta- t i o n s , w i t h p a r t i c u l a r a t t e n t i o n being paid to evidences of anisotropy and to appar- e n t l y anomalous e f f e c t s . The basic assumption i n j u s t i f y i n g the taking of the world- wide average j u s t described i s t h a t , w i t h proper s t a t i s t i c a l weighting of the s t a t i o n c o n t r i b u t i o n s , there should be no r e s i d u a l d i u r n a l v a r i a t i o n i n the world-wide f i g - ures, t h i s r e s u l t i s to be expected according to the many experiments which have es- tablished the world anisotropy of the solar d a i l y v a r i a t i o n and the r e l a t i v e l y neg- l i g i b l e amplitude of a sidereal d i u r n a l wave. Thus, such solar v a r i a t i o n s are smoothed by the averaging procedure. A set of l o c a l v a r i a t i o n s i s obtained, then, f o r each s t a t i o n , but these cannot be regarded m single d e t a i l w i t h great confidence, they do lend themselves en s u i t e most advantageously to the study of anisotropies, g i v i n g a powerful means f o r making world-wide comparisons. A f a m i l i a r e f f e c t accompanying Forbush decreases i s the increase of amplitude and advancement of phase of the d i u r n a l v a r i a t i o n that occurs a f t e r the s t a r t of the 87
COSMIC RAYS cosnac-ray storm. Of apparently equal i n t e r e s t and importance, i t was observed that the world-wide anisotropy e x i s t i n g f o r the d i u r n a l v a r i a t i o n i s considerably enhanced at the same time, and the phase s h i f t s seem t o be the same at a l l longitudes studied. F i f t e e n of such events were observed during the f i r s t ten months of IGY data. Further, not a l l geomagnetic storms are accompanied by Forbush decreases, but the enhancement of anisotropy" j u s t noted occurred a f t e r many sudden-commencement storm beginnings that were without Forbush e f f e c t i n the cosmic rays. This enhancement also accompanied a few gradual commencement events without accompanying Forbush decrease. Among several anomalous events, a p a r t i c u l a r l y unusual one was discovered to occur on December 23, 1957, during which time a strong increase of nucleonic i n t e n s i t y was observed at several European st a t i o n s near 0° longitude but which was t o t a l l y ab- sent at the s t a t i o n s l y i n g on the 15°-20'' longitude b e l t . The es s e n t i a l s of t h i s event were f i r s t noted from examination of the curves of the l o c a l v a r i a t i o n s calcu- lated as described above. Then the reduced d i r e c t observations from several a d d i t i o n a l s t a t i o n s were introduced i n t o the comparison, leading to the discovery of t h i s h i g h l y l o c a l i z e d s p a t i a l f l u c t u a t i o n o f i n t e n s i t y . Mr. Kaichi Maeda, who was i n active charge of t h i s phase of the work, l e f t the p r o j e c t i n October, 1959, a f t e r f i n i s h i n g h is Ph.D. t h e s i s . Another student (Mr. Tomoshige Suda) resumed the i n v e s t i g a t i o n , which i s described below i n the l a t t e r part of the section on studies of meteorological e f f e c t s . Collaboration w i t h Dr. Maeda (while at the U n i v e r s i t y of Maryland and at NASA) continued. From the very i n t e r e s t i n g anomalous events and patterns established i n the preliminary studies, i t i s q u i t e evident that very f r u i t f u l r e s u l t s can be expected from continued analysis of e x i s t i n g data and an extension of data-gathering and anal- y s i s through a representative part of the solar cycle. The search w i l l be extended i n t o the various sets of meson data w i t h regard to p a r t i c u l a r i n t e r e s t i n g e f f e c t s that have been i n i t i a l l y detected i n the more strongly v a r i a b l e low-energy nucleonic com- ponent. An extension of the c a l c u l a t i o n s w i l l be made to other l a t i t u d e b e l t s where l o n g i t u d i n a l s t a t i o n d i s t r i b u t i o n i s favorable, although the one used at 50° i s by fa r the best a v a i l a b l e . b. Cosmic-Ray Behavior During Onset of Geomagnetic Storms. A Chree analysis (method of superposed epochs) has been applied to the L i n c o l n neutron monitor data (15-minute recording epochs) f o r times associated w i t h ( i ) sudden commencement geo- magnetic storms and ( i i ) geomagnetic storms w i t h gradual commencement. The c a l c u l a - t i o n was performed f o r some 40 epochs per storm, centered upon the time of storm commencement. The so-called zero epoch i s the 15-minute recording i n t e r v a l i n c l u d i n g the commencement time. The c r i t e r i o n f o r s e l e c t i o n of geomagnetic events demanded re p o r t i n g by at least f i v e geomagnetic observatories, i n c l u d i n g Huancayo. Both of these analyses were subdivided i n t o two groups of events: (a) those which showed evidence of a Forbush decrease i n the d a i l y average i n t e n s i t y (33 events), and (b) those which showed no such evidence (41 events). A c o n t r o l analysis, u t i l i z i n g data from b a r o m e t r i c a l l y and geomagnetically quiet periods, was also made f o r purposes of determining the "normal" random f l u c t u a t i o n p a t t e r n of the departures of the super- imposed epochal values from the mean i n t e n s i t y of the epochs. The c a l c u l a t i o n s under s i t u a t i o n (b) showed f l u c t u a t i o n s that were reminis- cent of those found m the c o n t r o l analysis. I n contrast, both analyses under s i t u a - t i o n (a) showed d e f i n i t e time-dependent trends, i n c l u d i n g an apparent q u i e t i n g of f l u c t u a t i o n s during a 2-2 1/2 hour period approximately centered upon the zero epoch, followed by a lowered general l e v e l of i n t e n s i t y (Forbush decrease pattern) marked by a recurrent surging having a period o f about 11/2 hours and peak-to-peak amplitude of 1 1/2 per cent. (This amplitude i s more than three times the s t a t i s t i c a l standard e r r o r of the epochal departure from average.) The analyses c a r r i e d to a time 5 hours 88
COSMIC RAYS a f t e r storm connnencement, and three cycles of the surging occurred up to the end of t h i s time. An exc e l l e n t superposition of the two sets of r e s u l t s under s i t u a t i o n (a) was obtained when the sudden-commencement group (1) had i t s zero point s h i f t e d to a l a t e r time by one 15-minute epoch. This s h i f t put the main-phase commencement times of groups (1) and (2) i n t o closer consonance. A 30-minute (two epoch) s h i f t d i d not give qu i t e as good r e s u l t s . ( A c t u a l l y , the average duration of the sudden commencement preceding the main phase i s somewhere between 15 and 30 minutes.) I t would thus ap- pear that d e t a i l e d cosmic-ray behavior at the very beginning of a Forbush decrease i s not markedly d i f f e r e n t f o r the two species of geomagnetic storm commencement i f the time of main phase i s considered as the f i d u c i a l point of beginning. A corresponding Chree analysis of the values of the h o r i z o n t a l geomagnetic f i e l d i n t e n s i t y measured at Koror (geomagnetic equator) showed no resemblance to the d e t a i l s of the cosmic-ray surges. Apparently cosmic-ray n o n - s t a t i s t i c a l f l u c t u a t i o n s do not correspond i n short-time d e t a i l w i t h changing electromagnetic conditions near the e a r t h , but some uncertainty i n t h i s conclusion derives from the f a c t t h a t the eq u a t o r i a l e l e c t r o j e t f i e l d may have obscured short-term f l u c t u a t i o n s of the l o c a l general magnetic f i e l d . A quick comparison w i t h the Tucson magnetic data ( m i d - l a t i - tude) d i d not give reason to a l t e r the above conclusion, but a more d e t a i l e d calcu- l a t i o n I S to be c a r r i e d out w i t h the Tucson data. The L i n c o l n analysis has been extended to include l a t e r times on the Forbush decrease f r o n t s to study persistence and damping c h a r a c t e r i s t i c s of the observed p e r i - o d i c i t y . Twenty a d d i t i o n a l 15-minute epochs were used i n the extended analysis. The surging continued, w i t h some damping, but i t i s not yet possible to assign numerical parameters which c l e a r l y characterize the trends. The r e a l i t y of t h i s i n t e r e s t i n g e f f e c t i s not absolutely c e r t a i n , although the s t r i k i n g r e s u l t s of the re-superposition discussed above, when the zero epoch adjustment was made f o r the sudden commencement storms, gives a f a i r degree of confidence i n i t , the extension of the Li n c o l n calcu- l a t i o n s to post-IGY events and a good i n t e r n a t i o n a l sample should help decide the question. c. Studies of Meteorological E f f e c t s . I n v e s t i g a t i o n s of meteorological e f f e c t s on the mu-meson i n t e n s i t y deep i n the atmosphere have been made from both t h e o r e t i c a l and p r a c t i c a l standpoints. The Ph.D. thesis work of Kaichi Maeda (completed i n Octo- ber 1959) was l a r g e l y a t h e o r e t i c a l study of the d i r e c t i o n a l dependence of atmospheric temperature e f f e c t s on the hard component. A summary of t h i s work follows: To see the zenith-angle dependence of atmospheric temperature e f f e c t s , the c o e f f i c i e n t s of p a r t i a l temperature e f f e c t s (one r e l a t e d to decay and the other to absorption) were ca l c u l a t e d , these c o e f f i c i e n t s i n d i c a t e the c o n t r i b u t i o n s of temper- ature changes at d i f f e r e n t l e v e l s i n the atmosphere to the change of d i r e c t i o n a l i n - t e n s i t y of the muons at sea l e v e l . The c a l c u l a t i o n was based on the rigorous s o l u t i o n of the d i f f u s i o n equation of mu-mesons i n the standard atmosphere. The s u r v i v a l p r o b a b i l i t y of o b l i q u e l y - i n c i - dent muons i n the atmosphere was computed, taking i n t o consideration the n o n - l i n e a r i t y of i o n i z a t i o n loss vs. momentum i n the low-energy region and the logarithmic increase of r a d i a t i o n loss i n the r e l a t i v i s t i c high-energy region. I n t h i s computation the change of ze n i t h angle f o r s t r a i g h t meson t r a j e c t o r i e s a r i s i n g from the curvature of the earth's surface and atmosphere layers was p r e c i s e l y taken i n t o account. (This c o r r e c t i o n i s p a r t i c u l a r l y important at larger z e n i t h angles of a r r i v a l , where path length through the atmosphere i s not accurately represented i n terms of the cosine of the observed a r r i v a l angle.) The c a l c u l a t i o n f u r t h e r included ( i ) the geomagnetic d e f l e c t i o n of the muons i n the atmosphere, ( i i ) the generalized production spectrum of the muons, which gives proper z e n i t h a l dependence of muon i n t e n s i t y provided that 89
COSMIC RAYS i t I S corrected f o r m u l t i p l e Coulomb s c a t t e r i n g of muons i n the atmosphere, and ( i i i ) the c o n t r i b u t i o n of K-mesons to the p o s i t i v e temperature e f f e c t . Among the r e s u l t s found, the noteworthy points are as fol l o w s : ( i ) corre- sponding t o the e f f e c t i v e height of muon production, there i s a l e v e l of maximum con- t r i b u t i o n to the negative and p o s i t i v e temperature e f f e c t s , the height of which l e v e l increases w i t h increase of zen i t h angle, ( i i ) the negative temperature c o e f f i c i e n t averaged around the l e v e l of maximum c o n t r i b u t i o n shows a maximum at the zenith angle of approximately 75°, ( l i i ) the largest part of the p o s i t i v e temperature e f f e c t found from s t a t i s t i c a l analysis of muon data i s due to the change of the density d i s t r i b u - t i o n of the a i r , which causes a change of d i s t r i b u t i o n of momemtum loss f o r muons i n the atmosphere, ( i v ) the combined c o e f f i c i e n t of p o s i t i v e and negative temperature e f f e c t s i s approximately constant w i t h respect to atmospheric depth; hence a so-called "mean mass temperature" i s a good p r a c t i c a l approximation f o r the c o r r e c t i o n of cosmic- ray data f o r temperature e f f e c t s ; (v) geomagnetic d e f l e c t i o n of muons i n the atmos- phere i s not n e g l i g i b l e f o r the negative temperature e f f e c t even at middle l a t i t u d e s (50° geomag.), which leads to a larger temperature c o e f f i c i e n t f o r p o s i t i v e muons ar- r i v i n g from the east than f o r negative muons from the east, and v i c e versa f o r those a r r i v i n g from the west; since the geomagnetic c u t o f f momentum i s less f o r the west d i r e c t i o n , g i v i n g a r e l a t i v e l y higher i n t e n s i t y of low-energy muons from the west com- pared w i t h the east, the negative temperature e f f e c t as a whole i s larger f o r the west i n t e n s i t y than i t i s f o r the east, ( v i ) the c o n t r i b u t i o n of K-mesons i s such as to suppress the increase of the p o s i t i v e temperature c o e f f i c i e n t w i t h higher energy of observed muons. One of the objectives of the Moscow, 1959, meeting of the Subcommittee on Cosmic Ray I n t e n s i t y V a r i a t i o n s was to t r y to reach agreement on a method of correc- t i o n of meson data which would be standard f o r the i n t e r n a t i o n a l network of cosmic-ray s t a t i o n s r e p o r t i n g to the World Data Centers. Such agreement was not then possible, and a sub-subcommittee was created (of which the Project D i r e c t o r was a member) whose task I t was to make p r a c t i c a l c a l c u l a t i o n s on a s e l e c t i o n of representative IGY data so that a basis f o r f u t u r e recommendations could be l a i d . The L i n c o l n group p a r t i c i - pated i n these t e s t c a l c u l a t i o n s , but was delayed because of shortage of personnel, Mr. Suda, who a r r i v e d i n February, 1960, has completed them, and a report on the r e - s u l t s I S now being w r i t t e n . I t seems not possible to make a strong recommendation f o r a un i v e r s a l meson data c o r r e c t i o n scheme on the basis of the r e s u l t s . I t i s concluded, at least at present, that a p r a c t i c a l world-wide system cannot be e f f e c t i v e u n t i l the r e s u l t s of at least four radiosonde f l i g h t s per day are ava i l a b l e to supply aerolog- i c a l data t o c o n t r i b u t i n g cosmic-ray s t a t i o n s . Otherwise i t i s not possible to cor- r e c t the whole day's c o l l e c t i o n of meson data, but corrected data must be r e s t r i c t e d to those gathered during two or three hour epoch r e l a t e d to the radiosonde f l i g h t period. d. Some Special Events. Many extraordinary cosmic-ray events associated w i t h solar-geophysical a c t i v i t y were observed. Included amongst them was the complex of Forbush decreases and a solar i n j e c t i o n of low energy p a r t i c l e s occurring during July, 1959. The Li n c o l n s t a t i o n supplied special data to many colleagues who were making d e t a i l e d analyses of that sequence of events. This "July 1959 event" was the subject of i n t e n s i v e discussion at the meeting of lUGG m H e l s i n k i ( J u l y , 1960). The analysis of the solar i n j e c t i o n of May 4, 1960, i s the subject of two papers i n the Journal of Geophysical Research. Amongst other i n t e r e s t i n g p r o p e r t i e s , a d e f i n i t e c o r r e l a t i o n was detected between a change of the decay c h a r a c t e r i s t i c of the cosmic-ray i n t e n s i t y peak and the e x t i n c t i o n of the o p t i c a l part of the associ- ated solar f l a r e . Relationship of t h i s change to the occurrence of a secondary micro- wave peak i n the Type IV radio storm was apparently established. 90
COSMIC RAYS 6. Bibliography. a. Papers Presented at Meetings. R.L. Chasson, K. Maeda: "Local and World-Wide Cosmic-Ray Variations during Geomagnetic Storms and Small Geomagnetic Disturbances." V l t h I n t e r n a t i o n a l Cosmic Ray Conference, 1959, Moscow (published i n Proceedings, v o l . IV, p. 191). R.L. Chasson, K. Maeda: "Cosmic-Ray Behavior During Onset of Geomagnetic Storms." Meeting, American Phys. Soc, Pasadena, Dec, 1959 (publ. B u l l . Am. Phys. Soc. v o l . 4, p. 450, 1959). R.L. Chasson: "Families of Flare P a r t i c l e s on 4 May 1960," Proc 8th I n t ' l . Conf. on Cosmic Rays, v o l . I , December 1963, Jaipur. R.L. Chasson: "Fine Structure of Forbush Decreases," Proc. I n t ' l . Conf. on Cosmic Rays and the Earth Storm, J. Phys. Soc. Japan, v o l . 17, (Suppl. A - I l ) , p. 373, 1962. Anderson, Chasson, and Maeda: "Ch a r a c t e r i s t i c s of Solar-Flare Cosmic Rays and the Earth Storm, J. Phys. Soc. Japan, v o l . 17 (Supple. A - I I ) , p. 264, 1962. b. Published Papers. J.J. Schmidt, J r . : "A D i f f e r e n t i a l Counting Rate Meter f o r Low Counting Rates." M.A. Thesis, Un. of Nebraska, 1957. R.L. Chasson: "Significance of Cosmic Ray Monitor Observation." Geophys. and the IGY. pp. 71-80, AGU Monograph No. 2, July 1958. K. Maeda: " D i r e c t i o n a l Dependence of Atmospheric Temperature E f f e c t s on the Hard Component of Cosmic Radiation." Ph.D. Thesis, U n i v e r s i t y of"Nebraska, 1959, J. Atmos. Terr. Physics, v o l . 19, p. 184, 1960, under the t i t l e "Di- r e c t i o n a l Dependence of Atmospheric Temperature E f f e c t s on Cosmic Ray Muons at Sea Level." K. Maeda: "Production of Atmospheric Neutrons by Solar X ray," Nuovo Cimento. v o l . 20, p. 587-590, May 1, 1961. Anderson, Chasson, Liwschitz, and Suda: "The Solar Cosmic Ray Outburst of 4 May 1960." J ^ , v o l . 65, no. 12, Dec. 1960, pp. 3889-94. 91
COSMIC RAYS Project 2.16 - Neutron Monitor - Alaska 1. Objectives. A neutron monitor, constructed at the New York U n i v e r s i t y , was i n - s t a l l e d and operated at College, Alaska, to provide monitoring of the cosmic-ray f l u x at high l a t i t u d e , as part of an i n t e r n a t i o n a l network to observe f l u c t u a t i o n s i n the cosmic-ray f l u x as r e l a t e d to solar phenomena. The high l a t i t u d e locations were im- portant as only here can the lower energy cosmic rays be observed. 2. Operations. A neutron monitor of the Chicago-IUPAP design was constructed at NYU and i n s t a l l e d i n a b u i l d i n g near the campus of the U n i v e r s i t y of Alaska. Operation was a cooperative p r o j e c t of NYU and the Geophysical I n s t i t u t e of the U n i v e r s i t y of Alaska. The operation has continued since the end of IGY under a grant from the Na- t i o n a l Science Foundation. 3. Personnel. This p r o j e c t was under the d i r e c t i o n of S.A. K o r f f . Prof. Robert Haymes, and Messrs. W. Arthur, F. LaPeter and Mrs. M. Hommel have worked on the i n - struments and data. 4. Data. Data were reduced to the standard format prescribed by CSAGI and submitted to the IGY World Data Centers. 5. Results. The data showed several Forbush type decreases, each of larger ampli- tude but simultaneous i n time w i t h those observed at s t a t i o n s at lower l a t i t u d e s . I n a d d i t i o n , two increases were noted, neither of which showed at lower l a t i t u d e s . A study has been made of the July 1959 event as seen on t h i s meter. The monitor also showed increases on May 4, 1960 and on the November 1960 event, both of which are at present being analyzed f u r t h e r . 6. Bibliography. a. Papers Presented at Meetings. S.A. K o r f f and R. Haymes: "Observations of Cosmic Rays at the Time of the July 1959 Event." lAGA-UGGI, X l l t h Assembly, H e l s i n k i , July 25-August 6, 1960. R. Haymes and S.A. K o r f f : "Cosmic Ray Fluctuations i n Alaska." UGGI, X l l t h Assembly, H e l s i n k i , July 25-August 6, 1960. b. Published Papers. S.A. K o r f f : "Cosmic Ray Neutron Studies." Nuovo Cimento. v o l . 8, 1958, pp. 796-800. 92
COSMIC RAYS Projects 2.17, 2.18 - High A l t i t u d e Study of Spectrum and Time V a r i a t i o n of Neutrons and Primary Radiation 1. Obiectives. A series of high a l t i t u d e balloon f l i g h t s was planned by the cosmic- ray group at New York U n i v e r s i t y to i n v e s t i g a t e the charge and mass spectrum of the primary cosmic-ray f l u x , p a r t i c u l a r l y at times of solar disturbance, to determine whether the spectrum of p a r t i c l e s a r r i v i n g from the sun at these times would be the same as the normal spectrum. I n a d d i t i o n , other instrumentation was provided to search f o r neutrons of solar o r i g i n . 2. Operations. Lightweight t r a n s i s t o r i z e d equipment was developed and constructed at NYU. A special high p r e c i s i o n hypsometer was developed f o r p r e c i s i o n pressure deter- minations. Four balloon f l i g h t s were successfully completed at Brownwood, Texas, the balloons f l o a t e d as desired i n t o the night hemisphere to give d i u r n a l observations of the neutron component. Other f l i g h t s were made from Sioux F a l l s , S. Dakota, and the program was extended beyond the end of IGY. 3. Personnel. This p r o j e c t was under the supervision of S.A. K o r f f ; Arthur Beiser and Robert Haymes were the p r i n c i p a l senior s c i e n t i s t s associated w i t h Dr. K o r f f . Messrs. W. Reidy, W. Arthur, W. Christman, R. Kohl, and F. La Peter of the NYU s t a f f p a r t i c i p a t e d . 4. Data. Neutron data were worked up and published; i t has been submitted i n t h i s form to the IGY World Data Centers. 5. Results. As the balloons f l o a t e d i n t o the night hemisphere, a peak i n the neutron counting r a t e was observed j u s t before sunset; no great decrease i n counting r a t e a f t e r sunset was noted. One f l i g h t was made at the time of a solar disturbance and i t was noted that the i n t e n s i t y at high elevations was appreciably less than on the other f l i g h t s . I t was also noted, as other i n v e s t i g a t o r s also observed, that on these f l i g h t s the i n t e n s i t i e s were lower (by about twelve percent) than observed e a r l i e r i n the solar cycle. The slopes of the curves of neutrons as a f u n c t i o n of a l t i t u d e was d i f f e r e n t from e a r l i e r work i n d i c a t i n g that the absorption c o e f f i c i e n t f o r the nucle- onic component has increased from 180 to 240 gms/cm , Measurements of neutron i n t e n - s i t i e s were c a r r i e d to a l t i t u d e s of 37 km., which i s s u b s t a n t i a l l y higher than the 30 km. balloon a l t i t u d e s a t tained e a r l i e r . Fluctuations i n counting rates were noted at the times when strong auroral displays occurred and the balloon was at a l t i t u d e . 6. Bibliography. a. Papers Presented at Meetings. R. Haymes and S.A. K o r f f : "Cosmic Ray Neutrons at High Balloon A l t i t u d e . " B u l l . Amer. Phys. Soc. v o l . 5, p. 257, 1960. Amer. Phys. Soc. Meeting, Washington, D.C., 1960. S.A. K o r f f and R. Haymes: "Radiation Observed at Balloon Levels during Auroral Display." F o r t y - F i r s t Annual Meeting Amer. Geophys. Union, A p r i l 27, 1960, Washington, D.C. S.A. Korff,"Observations at College, Alaska, of the November 1960 Cosmic Ray Increases." J n l . Phys. Soc. of Japan, v o l . 17, Supplement A I I , (1962), pp. 303-306. I n t . Conf. on Cosmic Rays and the Earth Storm. R.C. Haymes, W.P. Reidy and S.A. K o r f f , "Cosmic Ray Neutron Densities at High Elevations," J n l . Phys. Soc. Japan, v o l . 17, Suppl. A I I , (1962), pp. 115-117, I n t . Conf. on CR and Earth Storm, Part I I . 93
COSMIC RAYS b. Published Papers. R.C. Haymes, H.L.L. van Passen: "A Precision Hypsometer f o r High A l t i t u d e Balloon F l i g h t s . " Dept. of Physics, Cosmic-Ray Group, New York U n i v e r s i t y , June 1958. G.B. Beiser, R.C. Haymes, S.A. K o r f f . "Research Ballooning." Dept. -of Physics, Cosmic-Ray Group, New York U n i v e r s i t y , Dec. 1, 1959. R. Haymes: "High A l t i t u d e Neutron I n t e n s i t y D i u r n a l V a r i a t i o n . " Phys. Rev., v o l . 116, pp. 1231-1237, 1959. R. Haymes: "Cosmic Ray Instrumentation f o r the IGY Program." Journ. Astro- naut .. v o l . 9, p. 64, 1957. S.A. K o r f f : "Geographical Aspects of Cosmic Ray Studies." Geographical Review, v o l . 50, pp. 504-522, 1960. R.C. Haymes and S.A. K o r f f : "Slow Neutron I n t e n s i t y at High Balloon A l t i - tudes." Phys. Rev., v o l . 120, pp. 1460-1462, 1960. S.A. K o r f f and R. Haymes: "High Neutron and Radiation I n t e n s i t i e s Observed during Auroral Display." JGR, v o l . 65, pp. 3163-3168, 1960. R. Haymes: "The World Wide IGY Cosmic Ray Program." Trans. NY Acad. Sci.. v o l . 22, pp. 96-103, 1959. S.P. Shen, S.A. K o r f f and Hugo A.C. Neuburg. "The T r i t i u m Content of Ant- a r c t i c Snow." Nature, v o l . 199, pp. 60-61, July 6, 1963. R.B. Mendell and S.A. K o r f f : "Fast Neutron Flux i n the Atmosphere." JGR. Vol. 68, pp. 5487-5495, (1963). J.L. Kamphouse: " C o r r e l a t i o n of the Neutron Monitor Pressure C o e f f i c i e n t and the Solar Cycle." JgR, v o l . 68, pp. 5608-5610, (1963). 94
COSMIC RAYS Project 2.19 - Balloon Emulsion Studies of Heavy Primary Cosmic Rays 1. Objectives. This p r o j e c t at the Department of Physics, U n i v e r s i t y of Washington, Sea t t l e , was concerned w i t h the determination of the heavy n u c l e i f l u x at several d i f - ferent l a t i t u d e s , i n order to get b e t t e r information on the energy spectrum of the primary r a d i a t i o n . Two general approaches were c a r r i e d out: a. The study of the abundance of primary cosmic-ray heavy nucl e i at r e l a t i v i s t i c v e l o c i t i e s w i t h stacks of nuclear emulsions exposed by free balloons near the geomag- net i c equator. b. The study, w i t h emulsions exposed by balloons at northern l a t i t u d e s , of the abundance of heavy primary n u c l e i stopping m the emulsion. 2. Operations. Work on the f i r s t method i s underway w i t h the analysis of a stack of emulsions exposed at an average e l e v a t i o n of 30.8 km on February 12, 1957, i n connec- t i o n w i t h the O f f i c e of Naval Research p r o j e c t EQUEX. The exposure was made near the isl a n d of Guam i n the P a c i f i c Ocean. A stack cons i s t i n g of a sandwich of G-5 and C-2 I l f o r d stripped emulsions was used to detect the primary heavy n u c l e i . Of the 24 emulsions i n the stack, 18 of them were of the G-5 v a r i e t y and developed i n the normal manner. The other 6 emulsions, located near the outer part of the stack, were of the C-2 type and were highly underdeveloped. The stack was placed i n a pressurized thin-walled aluminum container. This arrange- ment was then flown by free balloon from the v i c i n i t y of Guam. This f l i g h t which was at an el e v a t i o n of about 30.8 km f o r 7 hours provided a most s a t i s f a c t o r y exposure to the primary cosmic-ray heavy n u c l e i . 3. Personnel. This p r o j e c t was supervised and ca r r i e d out by J.J. Lord. 4. Data. The r e s u l t s of these studies have been published i n the Physical Review, v o l . 118, no. 3, pp. 828-830, May 1, 1960. 5. Results. The emulsions, exposed near Guam, were scanned w i t h a standard L e i t z microscope at a magnification of 210. A l l tracks longer than 600 microns m one emul- sion, and having an i o n i z a t i o n greater than 5 times the minimum were recorded. This method of scanning detects a l l primary cosmic-ray heavy nucl e i having an atomic num- ber of 3 (L i t h i u m n u c l e i ) or greater. Once the tracks were found, i t i s necessary to prove that they were due to primary cosmic-ray heavy nucl e i and not to slow protons and alpha p a r t i c l e s having a s i m i l a r i o n i z a t i o n . At the l a t i t u d e of Guam a l l primary heavy n u c l e i are quite r e l a t i v i s t i c and t h e i r i o n i z a t i o n remains constant as they traverse the stack of emulsions. Thus, by f o l l o w i n g each tra c k through the stack i t was possible to ascertain whether i t was associated w i t h a primary cosmic-ray heavy nucleus. About 800 tracks were considered and, of these, 112 were found to be of primary o r i g i n and u t i l i z e d i n t h i s experiment. Those tracks which were determined to be of primary o r i g i n were f u r t h e r i d e n t i f i e d by delta-ray measurements of t h e i r i o n i z a t i o n i n the G-5 emulsions and by grain-den- s i t y measurements of t h e i r i o n i z a t i o n i n the C-2 emulsions. C a l i b r a t i o n s f o r these determinations were obtained from r e l a t i v i s t i c L i t h i u m and Beryllium nu c l e i as w e l l as slow protons. 95
COSMIC RAYS Corrections to the analysis of the data obtained i n the above manner have to be made f o r : a. Loss of primary heavy n u c l e i due to c o l l i s i o n s w i t h a i r n u c l e i at elevations above those at which the stack was exposed. b. Fragmentation e f f e c t s where the c o l l i s i o n s w i t h a i r nucl e i r e s u l t i n the break-up of the primary p a r t i c l e i n t o elements of lower atomic number. c. V a r i a t i o n of the e l e v a t i o n of the balloon during the exposure of the stack. The calculated fluxes of heavy n u c l e i at the top of the atmosphere were found to be: L i , Be, B (L-nuclei) 0.26 ± 0.05 C, N, 0, F (M-nuclei) 0.66 j 0.10 Z > 10 (H-nuclei) 0.37-0.09 This f l i g h t took place on February 12, 1957 about a year p r i o r to the sun spot maxi- mum, however, there i s no evidence w i t h i n s t a t i s t i c a l e r r o r f o r any changes i n the composition of the primary heavy n u c l e i . 6. Bibliography. a. Papers Presented at Meetings. O.K. Krienke, D.D. Kerlee, J.J. Lord, M.E. Nelson: "Heavy P a r t i c l e Primary Cosmic-Ray Flux at the Geomagnetic Equator." 78th Meeting, Oregon Section, Am. Assoc. Phy. Sc. Teachers, Nov. 1958, Portland, Oregon. b. Published Papers. D.D. Kerlee, O.K. Krienke, J r . , J.J. Lord, M.E. Nelson: "Cosmic-Ray Heavy Nuclei at the Geomagnetic Equator." Phys. Rev., v o l . 118, May 1, 1960, pp. 828-30. 96
COSMIC RAYS Project 2.21 - The Semi-Diurnal Planetary V a r i a t i o n of Atmospheric Pressure 1. Obiectives. This p r o j e c t , as o r i g i n a l l y planned under the cognizance of the Department of Physics, U n i v e r s i t y of New Mexico, was to consist of an i n v e s t i g a t i o n i n t o the nature of the semi-diurnal planetary v a r i a t i o n of atmospheric pressures by means of recordings of the cosmic r a d i a t i o n at the surface and below ground. However, a pronounced twenty-four hour d i u r n a l v a r i a t i o n of the cosmic-ray count was found that overshadowed by f a r any semi-diurnal i n t e n s i t y v a r i a t i o n . The e f f o r t s were then s h i f t e d to an i n v e s t i g a t i o n of the 24-hr. d i u r n a l v a r i a t i o n because i t s presence made I t appear hopeless to t r y to study the semi-diurnal v a r i a t i o n , at l e ^ s t i n t h i s per- iod of high solar a c t i v i t y . 2. Operations. As the semi-diurnal pressure v a r i a t i o n has i t s maximum near the geo- graphic equator, and t h i s region i s f r e e r than temperate l a t i t u d e s of disturbance due to i r r e g u l a r v a r i a t i o n s i n the general c i r c u l a t i o n , cooperative arrangements were made w i t h the IGY Committee of B o l i v i a f o r observations at Chacaltaya, a high a l t i t u d e s c i e n t i f i c laboratory at 5240 m e l e v a t i o n . A v e r t i c a l , mu-meson telescope aperture 04°E-W, 48° N-S) was operated underground at a depth of 30 meters water equivalent. The counting rate was 5,000 t h r e e - f o l d coincidences/hour. 3. Personnel. This p r o j e c t was supervised by V.H. Regener; Dr. James F. Kenney and Abelardo Alarcon ( U n i v e r s i t y of La Paz) c o n s t i t u t e d the s c i e n t i f i c personnel associ- ated w i t h Dr. Regener. 4. Data. As t h i s was a special research p r o j e c t , not r e l a t e d to the synoptic pro- gram, the data were not reduced i n standard form f o r submission to the IGY World Data Center, but retained at the U n i v e r s i t y of New Mexico f o r analysis. 5. Results. The d i u r n a l v a r i a t i o n ^ as measured on 117 good recording days, was found to have an amplitude of 0.36 _ 0.057. w i t h a time of maximum at 15:08 mean solar time. As a r e s u l t of t h i s unexpected f i n d i n g , the work i s continuing at Chacaltaya under sponsorship of the National Science Foundation. The equipment has been modi- f i e d to provide an eastward looking and westward looking telescope. Provided that the v a r i a t i o n i s of e x t r a - t e r r e s t r i a l o r i g i n , the v a r i a t i o n should show up e a r l i e r i n the east telescope as a consequence of the earth's r o t a t i o n . Later r e s u l t s obtained at the same l o c a t i o n have confirmed the existence of such an anisotropy i n the cosmic ray f l u x . 6. Bibliography. a. Papers Presented at S c i e n t i f i c Meetings. V.H. Regener, J.F. Kenney: "Time V a r i a t i o n of Cosmic-Ray I n t e n s i t y Under- ground at Low L a t i t u d e . " Moscow Cosmic Ray Conference, lUPAP, July 1959. J.F. Kenney, V.H. Regener: "Solar Daily V a r i a t i o n of Cosmic Rays Under- ground Near the Geomagnetic Equator." Midwest Cosmic Ray Conference, Iowa C i t y , October 1959. V.H. Regener: "Solar Diurnal V a r i a t i o n of Cosmic Rays Underground Near the Geomagnetic Equator." I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm, Kyoto, Japan, September 1961. 97
COSMIC RAYS b. Published Papers. V.H. Regener, J.F. Kenney: "Time Vari a t i o n s of Cosmic Ray I n t e n s i t y Under- ground at Low L a t i t u d e . " Proc. Moscow Cosmic Ray Conf.. v o l . IV, pp. 216- 18, lUPAP, Moscow U n i v e r s i t y , 1960. V.H. Regener: "Solar Diurnal V a r i a t i o n of Cosmic Rays Underground Near the Geomagnetic Equator." Journ. Phys. Soc. Japan, v o l . 17, Suppl. A - I I , pp. 481-483, 1962. 98
COSMIC RAYS Project 2.22 - I s o t r o p i c C o n s t i t u t i o n of Cosmic Radiation at Balloon A l t i t u d e s 1. Objectives. This p r o j e c t at the Department of Physics and the Enrico Fermi I n s t i - t u t e f o r Nuclear Studies, U n i v e r s i t y of Chicago, was planned to study the heavy n u c l e i component i n the cosmic r a d i a t i o n , e s p e c i a l l y i n low energy regions of 700 Mev per nucleon and less. 2. Operations. An IGY f l i g h t was made at Prince A l b e r t , Canada through the coopera- t i o n o f the Canadian IGY Committee. The launching was handled by the Raven Corporation and I t took place on September 11, 1957. The balloon reached an a l t i t u d e of 37 km and stayed there f o r about 8 hours. The gondola c a r r i e d 200 p e l l i c l e s of 600-micron G-5 emulsion of dimensions of 10 x 15.2 m. The p e l l i c l e s were stacked v e r t i c a l l y w i t h a long side facing towards zeni t h . On top of the stack two h o r i z o n t a l plates w i t h a moving mechanism were placed i n order to study the time v a r i a t i o n of heavy primary fl u x e s . However, because the v i b r a t i n g reed of the D.C. motor was broken a f t e r about 5 hours from the launching, very l i t t l e could be learned about the f l u x v a r i a t i o n and hence i t w i l l be omitted from t h i s r e p o r t . The plates were processed i n Chicago and a f t e r about a h a l f a year of preliminary analysis they accompanied M. Koshiba to the I n s t i t u t e f o r Nuclear Studies at the U n i v e r s i t y of Tokyo f o r completion of the anal- y s i s , m f u l f i l l m e n t of a c o l l a b o r a t i v e agreement. 3. Personnel. This work was st a r t e d under the d i r e c t i o n of the l a t e Professor Marcel Schein; Masatoshi Koshiba assumed the r e s p o n s i b i l i t y a f t e r h i s death on February 20, 1960. Other personnel involved are H. Aizu, Y. Fujimoto, S. Hasegawa, I . Mito, J. Nishimura, and K. Yokoi. 4. Data. As these were special observations not included i n the guide f o r exchange of IGY data, the data w i l l not be reported here. However, they have been reported i n s c i e n t i f i c l i t e r a t u r e : r e f . Bibliography. 5. Results. Since the problem was to study the charge spectrum and the d i f f e r e n t i a l energy spectrum of the heavy n u c l e i m the low energy range, very r e l i a b l e i o n i z a t i o n measurements as w e l l as energy measurements were required. The i o n i z a t i o n was meas- ured by using: a. Calibrated blob density b. Gap density of v a r i e d minimum gap lengths c. 4-grain d e l t a ray counting d. Range c u t o f f d e l t a ray counting w i t h varying d e l t a ray ranges. Depending on the magnitude of the i o n i z a t i o n two or more of these methods were em- ployed f o r each track. Since the d e t a i l s of the c a l i b r a t i o n of each method and the interconsistency of r e s u l t s from d i f f e r e n t methods have been reported i n l i t e r a t u r e , a b r i e f resume of the r e s u l t s obtained i n t h i s work w i l l be given here. Figure 5 gives the energy spectra at the top o f the atmosphere f o r a p a r t i c l e s ; Lithium, Beryllium, Boron; Carbon, Nitrogen, Oxygen; Flourine to S i l i c o n , and Phos- phorus to Cobalt. Each i n d i v i d u a l p a r t i c l e has been corrected f o r the i o n i z a t i o n losses i n the r e s i d u a l a i r of 7.6 g/cm^. The fragmentation c o r r e c t i o n was also ap- p l i e d using the average of the fragmentation p r o b a b i l i t y a v a i l a b l e i n the l i t e r a t u r e . One can immediately notice the existence of maxima at about 600 Mev per nucleon i n any of the spectra. The s i m i l a r i t y i n the spectra shape from a to the highest 2 groups observed should be emphasized. This o v e r a l l s i m i l a r i t y i n spectra shape i s not only to be regarded as the extension of the s i m i l a r i t y law observed between the r i g i d i t y spectra of the proton and Ct component by McDonald, but also i n d i c a t i n g the f a c t that the i o n i z a t i o n loss i n the i n t e r s t e l l a r matter d i d not play a r o l e i n shaping the 99
COSMIC RAYS 50 .40- 30 20 'JO ' OB > 03 02 Points calculated assuming tlie shape of NC'Ejad+E)-" * ,â J for integral y spectrum Point invested using improved statistics Prince Albert (Sept 11,1957) - 4 - Minnesota ' (Moy 17,1957) -I- Sasl(atoon ' (June 18,1954) 100 200 300 400 600 1000 Energy of at air top Mev/nuc Figure 5. Energy Spectrum a t the Top of the Atmosphere f o r Alpha P a r t i c l e s and Heavier Components of the Primary Cosmic Ray Flux. 10 Ol .001 I I r" fromWeEjofE"'* for LiBeB.ob sortition and fragmentation in air corrected tromNfiE)«E - f P-Co - f F-Si - f CNO \ LiBeB 200 400 600 800 1000 Mev/nuc Energy at top of atmosphere Figure 6. Alpha P a r t i c l e Spectrum Compared w i t h other Determinates. ICQ
COSMIC RAYS spectra as such, since otherwise the p o s i t i o n of the maximum i n the high elements' .energy spectrum would have been observed to have s h i f t e d to much higher energies. A close i n v e s t i g a t i o n of the spectra seems to i n d i c a t e a s l i g h t d e v i a t i o n of the l i g h t and heavy component from the shape of the medium element spectrum, i . e . , the L:M r a t i o seems to be larger while the H:M r a t i o i s smaller i n the low energy region as compared w i t h t h e i r respective values at high energies. This r e s u l t was also con- firmed by our l a t e s t experiment using the stack exposed at Sioux F a l l s , South Dakota, on September 4, 1959, at an a l t i t u d e of 47 km. The r e s u l t s i n Table I g^ve the amount of matter traversed by the cosmic-ray p a r t i c l e s to be 3 g/cm and 5 g/cm f o r high energy and low energy p a r t i c l e s . This i s to be considered as i n d i c a t i n g that the i n t e r s t e l l a r Fermi-type acceleration i s i n e f f e c t i v e f o r these low energy p a r t i c l e s ; the conclusion which was a n t i c i p a t e d from the d i f f i c u l t y of overcoming i o n i z a t i o n loss of the heavy element. This r e s u l t i s i n support of the view that the cosmic-ray p a r t i c l e s have been accelerated much more e f f i c i e n t l y i n some l o c a l regions i n the galaxy and then d i f f u s e d through the i n t e r s t e l l a r magnetic i r r e g u l a r i t i e s to reach to the e a rth. Chemical abundance data are summarized i n Table I I . The abundances observed here i n the low energy region are i n e s s e n t i a l agreement, except f o r the small changes j u s t discussed, w i t h those at higher energies reported previously by us and other i n s t i t u - t i o n s , e s p e c i a l l y the overabundance of elements Z > 9 and the inverted abundance r a t i o of Carbon, Nitrogen, Oxygen, as compared w i t h the average cosmic abundance, has been confirmed here also f o r the low energy p a r t i c l e s . This leads to the conclusion that the same p a r t i c l e sources are responsible f o r the cosmic r a d i a t i o n of high and low energy. Furthermore, one should note t h e i r abundance anomalies, as were discussed m a previous p u b l i c a t i o n and also elsewhere, are i n support of the point of view that supernovae explosions are responsible f o r e j e c t i o n of these p a r t i c l e s , the conclusion which I S i n l i n e w i t h those a r r i v e d at above from the spectra shape. I n Figure 6 the Ot p a r t i c l e energy spectrum i s compared w i t h the r e s u l t s of other i n v e s t i g a t i o n s . A mechanism t o exp l a i n t h i s change of spectrum shape was given else- where, using the modulation e f f e c t of solar magnetic wind. I n combining these data w i t h those of the Sioux F a l l s exposure mentioned above, i t seems that maybe the 0!- p a r t i c l e spectrum should be divided i n t o two components, regarding the dip as r e a l m the spectrum at energies from 300 to 400 Mev per nucleon; i . e . , the higher energy com- ponent, which might be c a l l e d the g a l a c t i c component, behaves m p a r a l l e l w i t h the heavier n u c l e i , while the lower energy component, which might conveniently be termed as the solar component, changes r a p i d l y and by a s u b s t a n t i a l amount w i t h the solar a c t i v i t i e s . Obviously t h i s i n t e r p r e t a t i o n requires more d e t a i l e d observations under d i f f e r e n t conditions. The f i n a l remark i s that from the number of observed stopping p a r t i c l e s i n t h i s experiment the upper l i m i t f o r the anti-matter f l u x can be set at about 0.17. of or- dinary matter. This upper l i m i t , when we make use of the data of the other exposures, can be lowered by at least a f a c t o r of 3. 6. Bibliography. H. Aizu, Y. Fujimoto, S. Hasegawa, M. Koshiba, I . Mito, J. Nishimura, K. Yokoi, and Marcel Schein: "Heavy Nuclei i n the Primary Cosmic Radiation at Prince A l b e r t , Canada." Part I : Physical Review, v o l . 116, Oct. 15, 1959; Part I I : Physical Review, v o l . 121, Feb. 15, 1961, 1206-18. S. Hayakawa, M. Koshiba, and Y. Terashima: " I n t e r p r e t a t i o n of the Energy Spec- t r a of Heavy Primary Cosmic Rays." Proceedings of the Moscow Conference. 1959. S. Hayakawa and M. Koshiba: " O r i g i n of Cosmic Rays Revealed i n the R i g i d i t y Spectrum of Primary P a r t i c l e s . " Progress of The o r e t i c a l Physics, v o l . 21, 1959. 101
COSMIC RAYS Table 1 Ratios of L i g h t t o Medium and Heavy to Medium Components L/M H/M This experiment 200-700 Mev/nucleon 0.41 + 0.06 0.38 + 0.05 Texas experiment 1000 Mev/nucleon 0.32 + 0.07 0.48 + 0.10 Table I I Abundances of the Cosmic Ray Components TM U f f a r m t l a l n u n c ( t tha Top of AtoovlMr* (SaptMbn- U . 1957. F r l n a * UbCTt Staek) l a Unit of r u r t l e l M / i ^ . n o . ' s t a r , loo I t o v . < K) ac » 300 «< X) 5( » 7< » 800 900 1000 mn/mie. bl B* B 0.07*.0ll .Itt .OS .sa».o7 .m.os .4a*.oe .sat.o6 E ⢠0 .5U.08 .714.U .g6*.l8 .63t.l5 .33t.ll traa E'^'H r - a t .l6*.0l» .a3*.06 .15*.06 .IW.09 15 - 1 - as 1 .U*.05 .15*.0ll .084.04 00 (B > «00 H n) - 7.7*.7 t u r t l o l a ^ i ^ . B e a . s t t r . 080 (B i 800 Mar) ⢠D.St .S r ( r t l o l « « / i i ^ . M o . ( t * r . Inta^mtad F l n m of B l«a« i t ( at th* Tqp of AtnovtMn (800 5 B S 700 Itov/ime.) I n Unit of t i r t l e l o i / ^ . ⢠⢠« . i t o r . ⢠B e ⢠0 » â¢a Km HB u S I r a a A K Oa n 1 T 1 or 1 ito 1" 0.30 ±.oe .55 *.10 1.70 «.a5 t i l l 1.33 ⢠. 29 .06 *.05 .16 *.06 .03 *.03 .33 *.09 .06 *.05 .16 * .06 .05 t .03 .05 ⢠. 0 3 .08 ⢠. 0 8 .08 ⢠.08 .18 ⢠. 0 5 .on ⢠. 0 « .M . 0 « | .151 - â¢.otj*.ott|ft .o6| 3.e9*.)« .esA.is ~33*.09 .aTk.09 102
COSMIC RAYS Project 2.23 - Heavy Primary Cosmic Rays 1. Obiectives. This p r o j e c t at the Southern I l l i n o i s U n i v e r s i t y , Carbondale, I l l i - n ois, dealt w i t h emulsion studies of the cosmic-ray f l u x f o r primary n u c l e i w i t h Z equal to or greater than ten. The f o l l o w i n g questions were pursued: a. Flux at d i f f e r e n t a l t i t u d e s and l a t i t u d e s , b. Flux values extrapolated to top of atmosphere, c. Spectral d i s t r i b u t i o n ; d. Angular d i s t r i b u t i o n , e. Absorption c o e f f i c i e n t s f o r each Z; f. Mean free path f o r each Z, g. Values f o r a large number of tracks f o r s t a t i s t i c a l accuracy, h. Abundance r a t i o s of primaries of d i f f e r e n t Z values, 1. Comparison of r a t i o s i n (a) w i t h s i m i l a r r a t i o s f o r matter i n universe. J. Relationship between neutron i n t e n s i t i e s at the surface of the earth and heavy primary cosmic rays at high a l t i t u d e . 2. Operations. Emulsion packs were flown as hitchhikes on sky-hook balloons, p r i n - c i p a l l y i n cooperation w i t h Marcel Schein, J.A. Simpson, and Peter Meyer, U n i v e r s i t y of Chicago. Plates were scanned at Southern I l l i n o i s U n i v e r s i t y . This work was also supported by the U.S. Army Of f i c e of Ordnance Research. 3. Personnel. This p r o j e c t was under the supervision of O.B. Young. 4. Data. Data from many of the plates have been published and supplied to IGY World Data Center-A. 5. Results. The purpose of t h i s experiment was to determine what, i f any, r e l a t i o n - ship e x i s t s between v a r i a t i o n s of heavy cosmic-ray p a r t i c l e s of Z > 10 at the top of the atmosphere and v a r i a t i o n s of the neutron i n t e n s i t i e s at ground l e v e l . The v a r i a t i o n s i n question are assumed to be caused dominantly by changes i n solar a c t i - v i t y . Neutron information was obtained from the World Data Center from readings taken at the U n i v e r s i t y of Chicago and at Climax, Colorado. The cosmic-ray data were de- r i v e d from I l f o r d G.5 emulsions exposed under balloons flown at high a l t i t u d e s . The underlying experimental method was to determine both the neutron and cosmic- ray i n t e n s i t i e s f o r the times of the balloon f l i g h t s and then to compare t h e i r r e - spective r a t i o s f o r two balloon f l i g h t s made on d i f f e r e n t and c a r e f u l l y selected days. These r a t i o values then gave the percentage changes i n each the neutron and heavy cosmic ray i n t e n s i t i e s . For convenience the percentage was based on the denominator of the r a t i o f r a c t i o n . The heavy cosmic-ray primaries were i d e n t i f i e d by means of the delta-ray method of counting. The c r i t e r i a f o r counting included the 4 g r a i n minimum delta-ray length. Emulsion c a l i b r a t i o n included the i d e n t i f i c a t i o n of f l i g h t p a r t i c l e s from s c a t t e r i n g measurements. The d i f f e r e n t emulsions had i d e n t i c a l experiences i n being purchased i n the same l o t and i n being handled, stored, shipped and processed together. Even the f l i g h t s were nearly the same. The great solar storm on which t h i s experiment depends suddenly began August 29, 1957. While the Forbush decrease may have continued somewhat i n t o the 8G balloon f l i g h t period, t h i s e f f e c t i s regarded here too small to influence the conclusions. A t t e n t i o n i s c a l l e d to the f a c t that the r e s u l t s depend upon the values of r a t i o s . Therefore, absolute values were not necessarily obtained, e s p e c i a l l y f o r the f l u x at the top of the atmosphere. Consistency i n method of determining the numerator and 103
COSMIC RAYS the nominator of the r a t i o was imperative. A value of the r a t i o other than one i n d i - cates of course a change of value. Also I t I S to be noted that at the l a t i t u d e of Prince A l b e r t , Canada, some of the tracks are n o n - r e l a t i v i s t i c owing to the low c u t - o f f energy. However, the method was found to be i n s e n s i t i v e to the presence of n o n - r e l a t i v i s t i c tracks. The r a t i o was f i r s t determined as i f a l l tracks were r e l a t i v i s t i c , Then the r a t i o was determined by using a c o r r e c t i o n f a c t o r of 1.4 m the d e l t a ray count f o r a Z equal to 10. While the number of tracks decreased w i t h the use of the f a c t o r the r a t i o remained v i r t u a l l y unchanged. Again i t must be cautioned against using the f l u x values as absolute de- terminations. While 2000 heavy tracks are involved, which i s a large number f o r an experiment, the s t a t i s t i c a l value i s s t i l l too low to show conclusively whether the i n t e n s i t y of the heavy cosmic rays a c t u a l l y v a r i e d . Nevertheless, as the s t a t i s t i c a l l i m i t s of the r a t i o are w i t h i n s i x per cent, the conclusion f o r t h i s experiment surely can be drawn that the heavy cosmic rays d i d not vary nearly as much as the neutrons whose r a t i o showed a change of over 20 per cent. This conclusion i s f u r t h e r strength- ened by recent analysis of the data and by looking at r e s u l t s over the period 1952- 1963. The i n v e s t i g a t o r concludes that the heavy primary f l u x d i d not change over the solar cycle, i n d i c a t i n g independence of the heavy primary f l u x of magnetic c o n t r o l . There are grounds, the i n v e s t i g a t o r believes, f o r the assumption that the sun i s not a source of heavy primary ZIO. Following are the e s s e n t i a l data and conclusions r e s u l t i n g from a study of the e n t i r e emulsions. The angular d i s t r i b u t i o n chart f o r the heavy cosmic rays i s shown i n Figure 7. DATA AND COMPUTATIONS PLATE DATA: Plate #PA IC 2 #PA ID 2 F l i g h t 70 8G Date August 21, 1957 August 30, 1957 Location: Prince A l b e r t , Canada, GM Latitude 62° N. A l t i t u d e : 17.97 g/cm'Ì 15.3 gm/cm 92,000 f t . 95,200 f t . Duration of f l i g h t 8.45 hrs, 8.0 hrs. 2 2 Area scanned 194 cm 218.6 cm No, of tracks 796 1183 Emulsion type G-5 G-5 Emulsion thickness 600 microns 600 microns 104
COSMIC RAYS RESULTS: Case 1 . A l l heavy tracks t r e a t e d as r e l a t i v i s t l c . = 7 9 6 tracks = 1 1 8 3 tracks I Q = f l u x a t top o f atmosphere i n partl c l e s / m ^ sec. sterad. ^ I Q I = 3 . 2 1 7 + . 0 9 I Q2 = 3 . 0 9 2 + . 0 8 Ratio (R ) = _ 0 1 = 1 . 0 4 0 ^ I 0 2 V a r i a t i o n = 4% Case 2 . Correction f a c t o r of 1 . 4 used t o compensate f o r n o n - r e l a t i v i s t i c tracks: = 6 4 8 tracks = 9 4 6 tracks IQJ^ = 2 . 5 9 + . 1 = 2 . 4 8 + . 0 9 I Ratio (Rj) = _ 0 1 = 1 . 0 4 4 I 0 2 V a r i a t i o n = 4% NEUTRON DATA AND CALCULATIONS NOTE: The scale f a c t o r s at Chicago and Climax are not used f o r neutron counts as the r a t i o s would not be af f e c t e d . Average neutron counts per hour at time of f l i g h t 7 G : n^ (Chicago) = 1 5 0 8 n^ (Climax) = 3 0 4 7 Average neutron counts per hour a t time of f l i g h t 8 G : n2 (Chicago) = 1 2 5 5 n2 (Climax) = 2 4 7 4 Ratio r ^ (Chicago) = ^ = 1 . 2 0 " 2 V a r i a t i o n = 20% Ratio (Climax) = ^ = 1 . 2 3 V a r i a t i o n = 23% With v a r i a t i o n s of 4% at Prince A l b e r t i n the heavy cosmic rays, w i t h v a r i a - t i o n s of 20% and 23% i n the neutron i n t e n s i t i e s at Chicago and Climax, and w i t h a s t a t i s t i c a l upper l i m i t of 6%, the conclusion i s reached t h a t f o r t h i s experiment the heavy primary cosmic rays d i d not vary nearly as much as d i d the neutrons. 1 0 5
PA ID 2 Plate PA IC 2 Plate A l l tracks regarded r e l a t i v i s t i c 120 110 y 1001 0 90[ a w (T) 1 80 70 60 50 40 30 20 10 0 10 20 30 I4D 50 60 70 80 QO TOO Figure 7. Angular D i s t r i b u t i o n Chart f o r Heavy Cosmic Rays. 106
COSMIC RAYS 6. Bibliography. a. Papers Presented at Meetings. O.B. Young: "Indicated Conditions f o r Neutron Concentration and f o r Atoms w i t h Negative Nuclei i n Dense Stars." I l l i n o i s Academy of Sciences, May 3, 1957. O.B. Young, S. Tchejeyan: "Comparison of Delta Ray and Grain Counting Methods f o r I d e n t i f i c a t i o n of Heavy Cosmic Ray Nuclei i n Emulsions of D i f f e r e n t Sen- s i t i v i t i e s . " I l l i n o i s Academy of Sciences, May 3, 1957. O.B. Young, F. Zurheide: "Primary Heavy Cosmic Rays at G.M. La t i t u d e A'N." Meeting of American Physical Society, No, 28, 1958. O.B. Young, H.Y. Chen: "Heavy Primary Cosmic Rays from Texas Daytime F l i g h t s . " Annual Meeting of American Physical Society, Jan. 28, 1959. O.B. Young: "Atmospheric Neutrons." Physics Section, I l l i n o i s State Academy of Science, A p r i l 22, 1960. O.B. Young, T.P. Wang: "Relationship between Neutron I n t e n s i t i e s at the Sur- face of the Earth and Heavy Cosmic Rays at High A l t i t u d e s . " American Physi- c a l Society, A p r i l 25, 1960. b. Published Papers. O.B. Young, W. Ballowe. " C r i t e r i a f o r the Consistent Counting of Delta Rays on Heavy Nuclear Tracks i n Emulsion Plates." Amer. Jour, of Phys.. v o l . 24, no. 3, Mar. 1956, pp. 157-159. O.B. Young: "A Rare High Energy Photon J e t , " Phys. Rev.. v o l . 108, no. 3, Nov. 1, 1957, pp. 908-909. O.B. Young, F. Harvey: "Charge Spectrum, Mean Free Paths, and Flux of Heavy Primary Cosmic Rays at the Top of the Atmosphere." Phys. Rev.. v o l . 109, no. 2, Jan. 15, 1958, pp. 529-32. O.B. Young, H.Y. Chen: "Heavy Primary Cosmic Rays at Geomagnetic Latitude of 41°N." Phys. Rev., v o l . 115, no. 6, Sept. 15, 1959, pp. 1719-1721. O.B. Young, F. Zurheide: "Primary Heavy Cosmic Rays Near the Geomagnetic Equator." I I Nuovo Cimento. v o l . 14, Serie X, Oct. 1959, pp. 90-98. O.B. Young, T.P. Wang, P.C. Hsieh: "Constancy of Heavy Primary Cosmic Rays," Nuovo Cimento. Ser. X, v o l . 23, p. 101-107. O.B. Young, J.W. Lieh: "Heavy Primary Cosmic Rays During 1957," Nuovo Cimento. Ser. X, v o l . 31, pp. 974-77. 107
COSMIC RAYS Project 2.24 - Measurement of Zenith-Angle Dependence of High-Energy Mu-Mesons 1. Obiectives. This p r o j e c t at the Department of Physics, U n i v e r s i t y of Missouri, was set up to in v e s t i g a t e c e r t a i n unusual d e t a i l s i n the i n t e n s i t i e s of mu mesons at angles away from the v e r t i c a l at energies above 50-100 Bev. Preliminary t h e o r e t i c a l c a l c u l a t i o n s and experimental work had indic a t e d that there are remarkably more high- energy mu-mesons inc i d e n t at low a l t i t u d e s from o f f - v e r t i c a l d i r e c t i o n s than from the v e r t i c a l . This e f f e c t seemed to be understandable i n terms of competition between decay and absorption of pi-mesons high i n the atmosphere. Thus, i n a d d i t i o n t o the experimental determination of the mu-meson i n t e n s i t i e s , i t was planned to i n f e r some important d e t a i l s of the propagation of energetic pi-mesons and mu-mesons high i n the earth's atmosphere. 2. Operations. Detailed t h e o r e t i c a l studies yielded numerical r e s u l t s which were us e f u l i n the design of the experiments. The c a l c u l a t i o n s i n d i c a t e d that measurements of underground mu-meson i n t e n s i t i e s at great depths and large zenith angles would pro- vide u s e f u l r e s u l t s i f the experiments were c a r r i e d out w i t h the proper c o n f i g u r a t i o n of rock between the apparatus and ground l e v e l to provide i n t e g r a l energy di s c r i m i n a - t i o n . To t h i s end a series of s i t e s f o r a cosmic-ray telescope was selected deep w i t h i n a covered limestone quarry near Valmeyer, I l l i n o i s . The apparatus was designed to accept single penetrating p a r t i c l e s which had traversed hundreds of feet of rock (de- pending on the s i t e w i t h i n the quarry) and which had entered the rock on t r a j e c t o r i e s at z e nith angle 69° 1 3°, e s s e n t i a l l y perpendicular to a steep e x t e r i o r rock b l u f f bounding the quarry. The telescope consisted of three sets of crossed arrays of Geiger counters a meter apart and a f o u r t h t r a y of single counters arranged deeper i n the telescope behind a t h i c k s t e e l and lead s h i e l d . The f o u r t h t r a y provided d i s c r i m i n a t i o n against elec- trons and low energy mu-mesons which could be too g r e a t l y scattered i n the earth and counter materials. A l l counters were connected to a large hodoscope set, and the t r a j e c t o r i e s of mu-mesons through the apparatus were recorded photographically. The program of measurements has given the d i r e c t i o n a l i n t e n s i t y of single penetrating p a r t i c l e s at each of several oblique depths inside the quarry behind the steep exter- i o r b l u f f , a l l measurements w i t h i n the same zenith angle i n t e r v a l 66° - 72°. These i n t e n s i t i e s have been displayed on an i n t e n s i t y vs. depth p l o t to be compared w i t h known v e r t i c a l i n t e n s i t i e s at s i m i l a r depths. (See Sheldon and D u l l e r , 1962). A s i m i l a r experiment was then c a r r i e d out i n a mine near P r a i r i e du Rocher, I l l - i n o i s , w i t h a wider range of d i r e c t i o n s and be t t e r s t a t i s t i c s . 3. Personnel. This work was supervised and c a r r i e d out by N.M. D u l l e r , i n associa- t i o n w i t h J.A. Smith, W.R. Sheldon, O.L. Smith, and R.R. Kasten. 4. Data. As these were specialized experiments, the data were not amenable to t r e a t - ment given to other mu-meson monitor data and were not tabulated and submitted to the IGY World Data Centers. The r e s u l t s are ava i l a b l e to in t e r e s t e d workers upon request to the supervisor of t h i s p r o j e c t . Some t y p i c a l data from the work i n the second ex- periment are presented i n Section 5. 5. Results. The e x p e r i m t t a l r e s u l t s came from two separate but s i m i l a r experiments. The f i r s t one was ca r r i e d out at Valmeyer, I l l i n o i s , and i s described above (Section 3) and elsewhere (Sheldon and D u l l e r , 1962). The data r e s u l t i n g from the second underground experiment, at P r a i r i e du Rocher, I l l i n o i s , (150 meters above sea l e v e l ) are presented i n Table I I I . (O.L. Smith, 108
COSMIC RAYS Ph.D. Thesis, U n i v e r s i t y of Missouri, 1962). The underground c o n f i g u r a t i o n i n t h i s experiment i s q u i t e s i m i l a r to that i n the Valmeyer mine. The adjusted depth i n - cludes a standard equivalent v e r t i c a l atmosphere (only to f a c i l i t a t e comparison w i t h other data) and a l o c a l t h i c k s h i e l d which was traversed by a l l the p a r t i c l e s . The f r a c t i o n a l counts r e s u l t from a simple s t a t i s t i c a l treatment of events i n v o l v i n g small e l e c t r o n showers. The r e s u l t s of both experiments confirm a l l the e s s e n t i a l conclusions of the ear- l i e r t h e o r e t i c a l c a l c u l a t i o n s (Smith and D u l l e r , 1959). I n a d d i t i o n to these i n t e g r a l i n t e n s i t i e s of muons, inferences from the data include the f o l l o w i n g (R.R. Kasten, Ph.D. Thesis, U n i v e r s i t y of Missouri, 1962): i n t e g r a l and d i f f e r e n t i a l muon energy spectra, production spectrum of high-energy pions i n the atmosphere, absorption mean- free -path of high-energy pions m the atmosphere, and average muon energies at moder- ate depths underground as a f u n c t i o n of both depth and d i r e c t i o n . 6, Bibliography, a. Papers Presented at Meetings, J.A. Smith and N.M. D u l l e r : "Theory of Zenith-Angle V a r i a t i o n of the I n t e n - s i t y of High-Energy Mu-Mesons." B u l l e t i n of the American Physical Society, v o l , 3, no. 7, Nov, 1958, p, 362, W.R. Sheldon and N.M. D u l l e r . " I n t e n s i t y of High-Energy Mu-Mesons at Large Zenith Angles." B u l l e t i n of the American Physical Society, v o l . 5, no. 1 (Part I ) , January 1960, p. 23. W.R. Sheldon and N.M. D u l l e r : "High-Energy Cosmic Ray Mu-Mesons at Large Zenith Angles," Midwest Cosmic Ray Conference, St. Louis, Missouri, March 1961, O.L. Smith and N.M. D u l l e r : "Muons at Large Zenith Angles." B u l l e t i n of the American Physical Society, v o l . 7, no. 4, A p r i l 1962, p. 310. N.M. D u l l e r : "Cosmic Ray Muons at High Energies." I n v i t e d Paper before National Academy of Sciences, Austin, Texas, December 1962. R.R. Kasten and N.M. D u l l e r : "High-Energy Pions and Muons i n the Atmosphere." B u l l e t i n of the American Physical Society, v o l . 9, no. 2, Feb. 1964, p. 141. b. Published Papers. J.A. Smith and N.M. D u l l e r : " E f f e c t s of Pi-Meson Decay-Absorption Phenomena on the High-Energy Mu-Meson Ze n i t h a l V a r i a t i o n near Sea Level." JGR, v o l . 64, no. 12, Dec. 1959, pp. 2297-2305. W.R. Sheldon and N.M. D u l l e r : " I n t e n s i t i e s of Muons Underground at Large Zenith Angles." Nuovo Cimento. v o l . 23, Jan. 1962, pp. 63-76. O.L. Smith, R.R. Kasten, and N.M. D u l l e r : "Cosmic Ray Muons at High Energies." ( I n preparation.) 109
COSMIC RAYS Table I I I . Experimental data of an underground experiment at P r a i r i e du Rocher, I l l i n o i s , (near sea le v e l ) g i v i n g absolute cosmic ray muon i n t e n s i t i e s . Operating Rock Adjusted T o t a l T o t a l I n t e n s i t y s t a t i o n and thickness depth counts f r a c t i o n a l of muons Zenith (mwe) (mwe) counts ( p a r t i c l e s angle Error: ±27. cm" S t " sec _ r X 10^) 71° 81.6 96.9 215.0 14.0 18.01±1.23 74° 80.3 95.6 548.8 29.8 16.09± .69 77° 79.2 94.3 991.2 47.2 13.45± .43 1 80° 78.4 93.7 1089.5 46.5 11.09± .34 83° 77.8 93.1 879.5 21.5 7.93± .27 86° 77.3 92.6 343.9 12.9 5.16+ .28 89° 77.2 92.5 47.5 1.5 2.21± .32 71° 74° 77° 80° 83° 86° 89° 117.8 115.3 113.8 112.6 111.7 111.1 110.9 133.1 130.6 129.1 127.9 127.0 126.4 126.2 207.2 577.0 1018.8 1098.8 823.4 309.5 39.0 12.2 32.0 40.8 46.8 44.4 18.5 4.0 12.70± .88 11.081 .50 10.16+ 8.72i 6.49± 4.13± 1.66+ 32 26 28 23 26 71° 74° 77° 80° 83° 194.4 192.6 160.1 148.4 147.3 209.7 207.9 175.3 163.7 162.6 274.1 826.9 1364.3 816.9 217.7 17.1 40.9 64.3 49.9 16.7 7.131 6.74+ 7.53+ 6.66+ 5.66± ,43 ,23 .20 .23 .38 71° 250.6 265.9 266.8 10.8 5.23i .29 74° 239.5 254.8 794.8 37.8 4.88± .17 4 77° 226.5 241.8 1146.3 42.3 4.7&- .16 80° 208.6 223.9 774.2 31.2 4.751 .17 83° 176.1 191.4 231.1 12.1 4.53± .30 77° 356.7 372.0 672.1 31.1 2.51± .10 1 5 80° 334.2 349.5 422.7 20.7 2.331 .11 _1_ 83° 298.7 314.0 122.5 6.5 2.161 .19 6 68° 23.1 38.4 1149.9 33.9 56.3±1.7 110
COSMIC RAYS Project 2.25 - Solar E f f e c t s on Cosmic Rays at High A l t i t u d e s - A r c t i c 1. Obiectives. This p r o j e c t at the State U n i v e r s i t y of Iowa, provided f o r high a l - t i t u d e balloon measurements of cosmic-ray i n t e n s i t y , c a r r i e d out at a high l a t i t u d e during the IGY. En5)hasis was placed on regular long-duration balloon f l i g h t s , par- t i c u l a r l y during solar disturbances and aur o r a l a c t i v i t y i n order to obtain any cor- r e l a t i o n s of these events w i t h cosmic ray phenomena. a. Following types of measurements were planned: ( i ) The r a t e of a single Geiger counter, to measure the average omnidirec- t i o n a l charged p a r t i c l e i n t e n s i t y above a very low c u t o f f energy. ( i i ) The r a t e of a v e r t i c a l counter telescope, to measure the v e r t i c a l d i r e c - t i o n a l charged p a r t i c l e f l u x . ( l i i ) The t o t a l current of a Neher type i o n i z a t i o n chamber. ( i v ) The rate of a t h a l l i u m a c t i v a t e d Nal c r y s t a l ( f o r the 1958 f l i g h t s ) as an X-ray detector, w i t h c i r c u i t r y to count pulses w i t h lower l i m i t s of 40, 80, 160, 400 kev. b. The o r i g i n a l o bjectives of these f l i g h t s were: ( i ) To study the properties of the low energy end of the cosmic-ray energy spectrum, p a r t i c u l a r l y i t s time v a r i a t i o n over the period of one month (or one solar r o t a t i o n ) . More s p e c i f i c a l l y i t was desired to examine the time v a r i a t i o n of the en- ergy region t o which ground l e v e l neutron monitors are i n s e n s i t i v e . ( i i ) To study impact zone and small f l a r e e f f e c t s at n o r t h e r l y l a t i t u d e s . ( i i i ) To search f o r s o f t r a d i a t i o n at moderate atmospheric depths of 10 gm/cm . 2. Operations. Through the cooperation of D.C. Rose and the Canadian IGY Committee arrangements were made f o r a series of high a l t i t u d e balloon f l i g h t s from Fort Church- i l l , Canada. I t was hoped to achieve a more-or-less continuous monitor at high a l t i - tude of the cosmic ray f l u x and r e l a t e d phenomena. At the same time, monitor f l i g h t s were c a r r i e d out by the group at the U n i v e r s i t y of Minnesota at Minneapolis, at ap- proximately the same longitude but about 13° to the south. During the period of 7 August to 7 September 1957, fourteen high a l t i t u d e balloons bearing cosmic-ray instrumentation were launched from Fort C h u r c h i l l , Canada, l a t i t u d e 58.8°N., longitude 94.2° W. The t o t a l d u r a t i o n of these f l i g h t s which occurred w i t h - i n telemetering range was about 250 hours w i t h 175 hours occurring above 30 km a l t i - tude. F l i g h t s g i v i n g up to 25 hours of usable data were a t t a i n a b l e because of the low wind speeds at a l l a l t i t u d e s reached above 27 km. Between 10 August and 17 September 1958, twelve high a l t i t u d e , constant l e v e l balloons c a r r y i n g cosmic-ray instrumentation were launched from Fort C h u r c h i l l , Man- it o b a , Canada (Lat. 58.8°N, Long. 94.2°W). The purpose of these f l i g h t s was to ob- t a i n i n f o r m a t i o n on high l a t i t u d e cosmic ray e f f e c t s and X rays occurring i n connec- t i o n w i t h magnetic storms and other geophysical or solar phenomena. Approximately 150 hours of data were obtained above 30 km a l t i t u d e . To continue t h i s program of auroral zone measurements, f i v e f l i g h t s were made from Fairbanks, Alaska, during A p r i l 1959 under d i r e c t sponsorship of the ONR Skyhook program. The f l i g h t s were part of the U.S. program during IGC-59. This s i t e was chosen because of the very low 1 1 1
COSMIC RAYS ground winds encountered there which would f a c i l i t a t e launching large volume balloons. Such high a l t i t u d e f l i g h t s gave the p o s s i b i l i t y of studying X ray e f f e c t s at very small atmospheric depths. During July 1959 8 f l i g h t s were made from Resolute Bay, 160 km from the North Magnetic Pole, under NSF sponsorship and r e s u l t s on solar pro- tons obtained. Several f l i g h t s were also c a r r i e d out from Fort C h u r c h i l l i n August under ONR sponsorship. 3. Personnel. This work was supervised and c a r r i e d out by Kinsey A. Anderson (now at U. C a l i f , , Berkeley); D.C. Enemark and many other students were also associated w i t h the p r o j e c t and provided invaluable help. 4. Data. Reduced data from the C h u r c h i l l f l i g h t s were published and submitted to the IGY World Data Centers. 5. Results. The d i u r n a l v a r i a t i o n of the cosmic r a d i a t i o n was determined w i t h q u i t e high p r e c i s i o n w i t h the omnidirectional detector. As an example, during the f l i g h t of August 14, 195 7, the ion chamber showed an increase of 3,6 percent between 0800 and 1230 l o c a l time. During the cosmic-ray decrease of 29 August 1957, the change at a l t i t u d e as ob- served by the i o n i z a t i o n chamber was only a f a c t o r of two larger than e x h i b i t e d by the ground l e v e l neutron monitor at C h u r c h i l l . This rather small f a c t o r was a t t r i b u t e d to the high average energy of the cosmic r a d i a t i o n at sunspot maximum, and confirmed the high e f f i c i e n c y of the neutron monitor at such energies. These f l i g h t s also gave confirming evidence of the a n t i - c o r r e l a t i o n , discovered by Neher and Forbush, between cosmic-ray i n t e n s i t y and solar a c t i v i t y . Just previous to these f l i g h t s , the Minneapolis group (see p r o j e c t 2.12) discovered that s o f t r a d i - a t i o n (X rays) penetrated deeply i n t o the atmosphere. The C h u r c h i l l f l i g h t s uncovered two cases where s o f t r a d i a t i o n appeared; one case (August 29-30, 1957) was p a r t i c u - l a r l y s i g n i f i c a n t because i t occurred during the sudden commencement of a magnetic storm. This r e s u l t opened the p o s s i b i l i t y of c o r r e l a t i v e studies w i t h other geophys- i c a l phenomena. The event of September 1-2, 1957, was not associated w i t h a magnetic disturbance, although i t occurred i n a period of considerable solar a c t i v i t y . The r a d i a t i o n was apparently present before the balloon reached c e i l i n g a l t i t u d e and was s t i l l detectable twelve hours l a t e r . The i o n chamber to single counter r a t i o under- went changes by a f a c t o r of three during the f l i g h t s , p a r t i c u l a r l y i n the e a r l y p a r t . During the greater part of the event, t h i s r a t i o was c h a r a c t e r i s t i c of 100 kev X rays but at times solar protons of average energy 50 to 100 mev at the detectors were prob- ably present. On August 22, 1958, the occurrence of i o n i z i n g r a d i a t i o n was observed i n time as- s o c i a t i o n w i t h a great continuum radio noise storm on the sun. The rates of the i o n chamber and counter telescope rose by as much as a f a c t o r of ten above the cosmic-ray l e v e l while the single counter increased by a much smaller f a c t o r . These r a t i o s could not be obtained w i t h X rays, high energy gamma-rays or electrons, but could be explain- ed by protons of 170 mev energy. The a r r i v a l of these protons, f o l l o w i n g a solar se- quence of o p t i c a l f l a r e , radio noise bursts, and long enduring noise storm, continued to be observed f o r at least two days. From the resemblance of the continuum radio noise emission t o the observed p a r t i c l e i n t e n s i t i e s i t was deduced th a t the cosmic ray storage took place i n the solar atmosphere. The i n t e r p r e t a t i o n of the Fort C h u r c h i l l r e s u l t s was published i n 1958 and estab- lished f o r the f i r s t time solar production of nucleonic p a r t i c l e s i n the energy region 100 to 300 Mev. Shortly a f t e r the preliminary r e s u l t s were published the r e l a t i o n of these solar p a r t i c l e fluxes to the absorption of g a l a c t i c radio noise i n riometers located i n the polar regions was noticed. This led to a very r a p i d development of the study of low energy solar cosmic rays. 112
COSMIC RAYS Simultaneous balloon f l i g h t s by the Minnesota cosmic ray group at Minneapolis g r e a t l y extended the conclusions t h a t could be drawn from t h i s experiment. The pres- ence of Explorer IV i n i t s o r b i t also added very s u b s t a n t i a l l y to the experiment and represented the f i r s t time that the simultaneous use of the balloon and s a t e l l i t e techniques yielded important s c i e n t i f i c r e s u l t s . 6. Bibliography. a. Papers Presented at Meetings. The r e s u l t s of the pr o j e c t were described at various meetings, i n c l u d i n g , American Physical Society meeting i n St. Louis, Nov. 1957, Washington, D.C., 1958, 1959 and I960, the Mid West Cosmic Ray Meeting, Iowa C i t y , October 1959; and the COSPAR Space Science Symposium, Nice, France, February 1960. b. Published Papers. K.A. Anderson: "Occurrence of Soft Radiation During the Magnetic Storm of 29 August 1957." JGR, v o l . 62, 1957, pp. 641-44. K.A. Anderson: "Soft Radiation Events at High A l t i t u d e during the Magnetic Storm of August 29-30, 1957." Phys. Rev., v o l 111, no. 5, Sept. 1, 1958, pp. 1397-1405. K.A. Anderson: " I o n i z i n g Radiation Associated w i t h Solar Radio Noise Storm." Phys. Rev. L e t t e r s , v o l . 1, no. 9, Nov. 1, 1958. K.A. Anderson, R. Arnoldy, R. Hoffman, L. Peterson, J.R. Winckler: "Observa- ti o n s of Low Energy Solar Cosmic Rays from the Flare of 22 August 1958^" JGR. v o l . 64, no. 9, Sept. 1959, pp. 1133-48. K.A. Anderson, D.C. Enemark: "Balloon Observations of X-Rays i n the Auroral Zone I . " JGR, v o l . 65, no. 2, Feb. 1960, pp. 551-64. K.A. Anderson, D.C. Enemark: "Balloon Observations of X-Rays i n the Auroral Zone I I . " JGR, v o l . 64, no. 11, Nov. 1960, pp. 3521-38. D.C. Enemark, K.A. Anderson: "Instrumentation f o r Auroral Zone Balloon Ex- periments and Summary of F i e l d Operations." Phys. Dept., State Univ. of Iowa, Report SUI-59-17, June 1959. K.A. Anderson: "Solar P a r t i c l e s and Cosmic Rays." S c i e n t i f i c American, v o l . 202, no. 6, 1960, pp. 64-71. K.A. Anderson and D.C. Enemark: "Observations of Auroral Zone X-Rays and Solar Cosmic Rays." Proc. of the F i r s t I n t e r n a t i o n a l Space Science Symposium. Amsterdam 1960, p. 702. K.A. Anderson and D.C. Enemark: "Observations of Solar Cosmic Rays Near the North Magnetic Pole." JGR, v o l . 65, 1960, p. 2657. 113
COSMIC RAYS Project 2.28 - Neutron Monitor - Thule 1. Objectives. This p r o j e c t , undertaken by B a r t o l Research Foundation of the F r a n k l i n I n s t i t u t e , provided f o r the c o n s t r u c t i o n and i n s t a l l a t i o n of a neutron monitor, as part of an i n t e r n a t i o n a l network of ground l e v e l cosmic ray monitors f o r the IGY. The p i l e was i d e n t i c a l i n design to that at Resolute, Canada, so that a d e t a i l e d study, i n cooperation w i t h Canadian s c i e n t i s t s , of time v a r i a t i o n s and d i s t i n c t i v e events was possible at locations near the geomagnetic pole but at widely d i f f e r e n t longitudes. 2. Operations. The equipment was i n s t a l l e d on the Thule A i r Base, at a f i e l d s i t e operated by the U.S. Army Signal Corps Radio Propagation Agency, personnel of which operated the equipment. 3. Personnel. This work was under the supervision of M.A. Pomerantz. V.R. Potnis was the p r i n c i p a l s c i e n t i s t involved i n the reduction of data. 4. Data. Data were reduced according to the CSAGI plan and submitted to the IGY World Data Centers. 5. Results. A general o v e r a l l decrease of about 7.57. m cosmic-ray i n t e n s i t y was ob- served i n the period August 1957 - August 1958. Numerous Forbush-type decreases were also observed. The m a j o r i t y of these were accompanied by magnetic storms, most of which were of the sudden commencement type. The cosmic-ray events were characterized by a very r a p i d f a l l , followed by a gradual recovery. The events i n October 1957 and January and March 1958 were not accompanied by any type of magnetic disturbance. A number of f l a r e s of importance 3+ occurred but no r e l a t e d cosmic-ray increases were observed. Excellent c o r r e l a t i o n was found between measurements at Resolute and Thule, a l - though there were s t r i k i n g cases where the respective changes were opposite i n phase. During August 1957, the c o r r e l a t i o n c o e f f i c i e n t between Thule and Ottawa was +0.98. A s i g n i f i c a n t d i u r n a l v a r i a t i o n outside of atmospheric disturbances has been observed at Thule. The d i u r n a l amplitude i s s l i g h t l y smaller than that observed at Resolute. I t i s d i f f i c u l t to understand a d i u r n a l v a r i a t i o n near the pole. T h e o r e t i c a l calcu- l a t i o n s have been made w i t h the UNIVAC computer, and i t i s found that the f a c t that the magnetic axis does not coincide w i t h the axis of r o t a t i o n of the earth may be r e - sponsible f o r observed d i u r n a l v a r i a t i o n at Thule. The mean year l y amplitude (Aug. 57 - July 58) at Thule i s .097. and the time of maximum i s at 1312 hours l o c a l time. This experimental r e s u l t i s being studied along w i t h the r e s u l t s of other IGY s t a t i o n s to f i n d the energy spectrum of the d a i l y v a r i a t i o n . This study w i l l also i n d i c a t e i f there i s any lower l i m i t of energy below which there i s no d i u r n a l v a r i a t i o n of cosmic rays. 6. Bibliography. K. Nagashima, V.R. Potnis, M.A. Pomerantz: "Theoretical C a l c u l a t i o n of the Solar D i u r n a l V a r i a t i o n of the Cosmic-Ray I n t e n s i t y . " Nuovo Cimento. 1961 ( i n press). S.P. Duggal, K. Nagashima, M.A. Pomerantz: " R i g i d i t y Dependence of Solar Diur- nal V a r i a t i o n of Cosmic Ray I n t e n s i t y . " J. Geophys. Research ( i n press). M.A. Pomerantz, S.P. Duggal, and K. Nagashima: "Solar D i u r n a l V a r i a t i o n of Cos- mic Ray I n t e n s i t y . " Journal of the Physical Society of Japan, v o l . 17, Suppl. A - I I , pp. 464-468, I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm, (1962). S.P. Duggal and M.A. Pomerantz: "Diurnal V a r i a t i o n of Cosmic Rays Near the Geomagnetic Poles." Proceedings of the I n t e r n a t i o n a l Conference on Cosmic Rays, Jaipur, I n d i a , December 2-14, 1963. 114
COSMIC RAYS Project 2.29 - Energy and Charge Spectrum of Primary Cosmic Radiation 1. Objectives. This p r o j e c t at the U n i v e r s i t y of Rochester provided f o r the exposure of large stacks of stripped emulsion at high geomagnetic l a t i t u d e s , where the a p r i o r i r i g i d i t y i s expected t o be low, and a t high a l t i t u d e s corresponding to a r e s i d u a l over- head mass of less than 8 gm/cm^, f o r periods of eight to sixteen hours. I t was planned to i n v e s t i g a t e the proton energy spectrum at energies equal to or less than 700 Mev; to search f o r primary D, H^ and He3; to determine the low energy end of the heavy par- t i c l e spectrum (Z equal to or greater than 2 ) ; to study i n t e r a c t i o n s of n u c l e i of Z equal t o or greater than 2; t o study very high energy i n t e r a c t i o n s . 2. Operations. The emulsion stacks were planned to be flown i n such a manner that they would be positioned i n the proper geometry only a f t e r the balloon had reached f l i g h t a l t i t u d e . To t h i s end a mechanism (stack f l i p p e r ) was constructed at Rochester and i n s t a l l e d i n a large p l a s t i c gondola purchased from L.C. Renslow of St. Paul, Min- nesota. Associated timing and pressure recording apparatus was purchased from Raven I n d u s t r i e s , Sioux C i t y , South Dakota. The e n t i r e assemblies when prepared f o r f l i g h t weighed approximately 70 Kg. Two separate balloon f l i g h t s were obtained. The f i r s t f l i g h t ( I ) package consisted of 150 - 25cm x 30cm x 400 micron and 125 - 25cm x 30cm x 600 micron I l f o r d G-5 s t r i p - ped emulsions packed as a single u n i t . The 150 - 400 micron emulsions are the con- t r i b u t i o n s of t h i s laboratory, 90 of the 600 micron emulsions are the c o n t r i b u t i o n s of Dr. M. Friedlander of Washington U n i v e r s i t y , St. Louis, Mo. (performing research under AF Contract No. AF 18(603)-108 and 35 of the 600 micron emulsions were exposed f o r Dr. Charles Dahanayake of the U n i v e r s i t y of Ceylon, Colombo, Ceylon. I t was f e l t t h at the assembly of t h i s large amount of emulsion i n t o one stack enhanced the value of the whole. The exposure was w i t h the 25cm edge h o r i z o n t a l . The second f l i g h t ( I I ) package consisted of 150 - 25cm x 20cm x 600 micron I l f o r d G-5 stripped emulsions and was exposed w i t h the 20 cm edge h o r i z o n t a l . F l i g h t I was launched from Minneapolis, Minnesota (geomagnetic l a t i t u d e 55° N), on J u l y 30, 1957. The plane of the emulsions was held h o r i z o n t a l u n t i l a f t e r the b a l - loon had reached c e i l i n g at which time i t was rot a t e d 90°. The e f f e c t i v e c o l l e c t i o n time at a l t i t u d e f o r cosmic ray events was 8 hr. 31 min. w i t h the average amount of re s i d u a l atmosphere above the balloon being 8.5 gm/cm^; to account f o r the packing m a t e r i a l and the 1/4" f i b r e glass gondola, the e f f e c t i v e amount of overhead m a t e r i a l was 8.8 gm/cm^. Launch time was 06:30 l o c a l , a l t i t u d e a t t a i n e d at 08:27 and gondola released at 17:55. F l i g h t I I was launched from Neepawa, Manitoba, Canada (geomagnetic l a t i t u d e 61° N) on 3 August 1958. The f l o a t i n g a l t i t u d e corresponded t o 3.5 gm/cm^ of re s i d u a l a t - mosphere and w i t h the packing and gondola m a t e r i a l , the e f f e c t i v e amount o f overhead m a t e r i a l was 3.8 gm/crxr. The e f f e c t i v e exposure time at a l t i t u d e was 8 hours and 30 minutes. Launch was at 05:10 ( l o c a l ) , a l t i t u d e a t t a i n e d at 08:00 and cut down at 16:30. Both operations were arranged v i a the ONR Skyhook Program administered by Commander Cochran of the U n i v e r s i t y of Minnesota. 3. Personnel. This p r o j e c t was under the supervision of M.F. Kaplon. P a r t i c i p a t i n g personnel at the U n i v e r s i t y of Rochester included M.V.K. Appa Rao, A. Engler, A. Kernan, J. Klarmann, and P.J. Lavakare. These p h y s i c i s t s p a r t i c i p a t e d i n various as- pects of data reduction and analysis. 4. Data. Data i s contained i n work submitted f o r p u b l i c a t i o n (see Bi b l i o g r a p h y ) . 115
COSMIC RAYS 5. Results. The i s o t o p i c composition of low energy helium n u c l e i was determined i n the emulsion stacks of both F l i g h t s I and I I by using the "constant s a g i t t a " s c a t t e r - i n g method on tracks of helium n u c l e i stopping i n the nuclear emulsion. For F l i g h t I the c r i t e r i a applied was to accept tracks w i t h z e n i t h angles less than 30°, p o t e n t i a l range of 30 cm. and a minimum range of 4.5 cm. For F l i g h t I I the c r i t e r i a were z e n i t h angles less than 45° and minimum range of 4 cm. I d e n t i c a l experimental procedures i n measurement were applied i n both cases. For both f l i g h t s , there was no i n d i c a t i o n of unusual solar a c t i v i t y . For F l i g h t I the r a t i o R = He^/(He-* + He^) was found to be 0.41 ± 0.09 f o r the en- ergy per nucleon range of 200 to 400 Mev and 0.36 i 0.11 f o r the magnetic r i g i d i t y range, 1.3 to 1.6 Bv. The c o r r e c t i o n f o r production of secondary He^ i n the r e s i d u a l atmosphere was estimated to be 4%,. On the assumption of the non-existence of He i n the primary cosmic ray sources and tha t the observed He-Ì r e s u l t s from s p a l l a t i o n of higher mass n u c l e i during t h e i r g a l a c t i c t r a v e l , the above f i g u r e s correspond to a t r a v e r s a l of 14 - 3gm/cm2 and 12.2 - 3.5 gm/cm2 re s p e c t i v e l y of i n t e r s t e l l a r m a t e r i a l . For F l i g h t I I the r a t i o R was determined to be 0.31 ± 0.08 f o r the energy per nu- cleon range of 160-355 Mev, and 0.33 ± 0.08 f o r the magnetic r i g i d i t y range 1.05-1.48 Bv. These values are consistent w i t h those observed on F l i g h t I and imply t h a t the observed He-Ì does not represent a phenomena of l o c a l production w i t h i n the solar system. I n F l i g h t I the He energy spectrum was inv e s t i g a t e d as w e l l as the absolute f l u x . The d i f f e r e n t i a l energy spectrum was observed to have a broad maximimi between 400 and 600 Mev/nucleon and appeared to be d i f f e r e n t i n shape from the spectra observed at solar minimum. The t o t a l f l u x was observed to be 151 ± 9 He nuclei/m2 sec. s t e r . above the c u t - o f f value f o r the f l i g h t l a t i t u d e . No p a r t i c l e s were observed to have k i n e t i c energies below 200 Mev/nucleon. From the centered dipole approximation one would expect a c u t - o f f at 292 Mev/nucleon; the r e s u l t s disagree w i t h t h i s but do not allow a choice to be made between other models. On F l i g h t I I measurements were made to determine the existence of primary deuter- ons and t r i t o n s . The g r a i n density vs. range method was used f o r the i d e n t i f i c a t i o n . The s e l e c t i o n c r i t e r i a allowed the observation of deuterons of k i n e t i c energy between 92 and 175 Mev/nucleon and t r i t o n s between 73 and 165 Mev/nucleon. The upper l i m i t s f o r the d i f f e r e n t i a l f l u x e s , i n the ranges defined, were 3.5 x 10"3 and 9.2 x 10"3 part i c l e s / m sec. s t e r . Mev f o r deuterons and t r i t o n s r e s p e c t i v e l y . The upper l i m i t f o r the t r i t o n to He r a t i o f o r the same r i g i d i t y (1.14 t o 1.48 Bv) i s 0.09. Due t o the u n c e r t a i n t y i n the c o r r e c t i o n f o r secondary production w i t h i n the atmosphere, the r e s u l t s are consistent w i t h the absence of these elements w i t h i n the primary cosmic r a d i a t i o n . An a d d i t i o n a l comment about the He r e s u l t s may be made at t h i s p o i n t . Further ex- periments w i t h respect to determining the r a t i o R at low energies have been c a r r i e d out both at Rochester and at other l a b o r a t o r i e s . I n a d d i t i o n the r a t i o of the l i g h t elements (L) 3< Z< 5 to the medium n u c l e i (M), 6 < Z< 9 have been c a r r i e d out as a f u n c t i o n of energy, again both at Rochester and at other l a b o r a t o r i e s . These i n d i - cate that the r a t i o L/M increases w i t h decreasing energy and support the observation of a f i n i t e amount of He-Ì i n the primary r a d i a t i o n . I n conjunction w i t h a lowered r a t i o of L/M at higher energies these r e s u l t s imply that the cosmic r a d i a t i o n at lower energies has traversed more matter than t h a t a t higher energies. Whether t h i s r e - f l e c t s p r o p e r t i e s of the source region or of the i n t e r s t e l l a r region i s not yet clea r and a d d i t i o n a l measurements as w e l l as t h e o r e t i c a l c a l c u l a t i o n s need yet to be done. 116
COSMIC RAYS Bibliography. a. Papers Presented at Meetings. M.V.K. Appa Rao and M.F. Kaplon: "He^-Nuclei m the Primary Cosmic Radiation." Journal of the Physical Society of Japan, v o l . 17, Supplement A - I I I , 1962, I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm, Part I I I , pp. 48-52, January 1962. M.F. Kaplon: " I s o t o p i c Composition." Journal of the Physical Society of Japan, v o l . 17, Supplement A - I I I , I n t e r n a t i o n a l Conference on Cosmic Rays and the Earth Storm, Part I I I , pp. 68-73, January 1962. M.V.K. Appa Rao: " I s o t o p i c Composition of Low Energy He Nuclei i n Primary Cosmic Radiation." Am. Phys. Soc, New York January 1961. b. Published Papers. M.V.K. Appa Rao and M.F. Kaplon: "The Influence of I s o t o p i c Composition on the Maximum i n the Cosmic Ray Energy Spectra." I I Nuovo Cimento. Series X, v o l . 21, pp. 369-372, 16 July, 1961. A. Engler, M.F. Kaplon, A. Kernan, J. Klarmann, C.E. F i c h t e l and M.W. F r i e d - lander: "Primary Cosmic Ray a - P a r t i c l e s - I , " I I Nuovo Cimento. Series X, v o l , 19, pp. 1090-1099, 16 March 1961. M.V.K. Appa Rao: "The He"Ì / (He^ + He^ Ratio i n Primary Cosmic Radiation." Journal of Geophysical Research, v o l . 67, no. 4, pp. 1289-1293, A p r i l 1962. M.V.K. Appa Rao and P.J. Lavakare: "The Abundance of T r i t o n s and Deuterons i n Primary Cosmic Radiation." I I Nuovo Cimento. Series X, v o l . 26, pp. 740-747, 16 November 1962. M.V.K. Appa Rao: " I s o t o p i c Composition of the Low-Energy Helium Nuclei i n the Primary Cosmic Radiation." The Physical Review, v o l . 123, no. 1, pp. 295-300, 1 July 1961. 117
COSMIC RAYS Project 2.30 - Neutron I n t e n s i t y Time V a r i a t i o n 1. Objectives. This p r o j e c t at the Department of Physics, U n i v e r s i t y of New Hamp- sh i r e , provided f o r reduction of data from neutron monitor i n s t a l l a t i o n s at Durham, N.H., and Mt. Washington, the operations of which were supported by non-IGY funds. The f o l l o w i n g i n t e n s i t y - t i m e v a r i a t i o n s were studied: a. 27-day p e r i o d i c i t y b. d i u r n a l v a r i a t i o n c. increases associated w i t h solar f l a r e s d. decreases observed w i t h geomagnetic f i e l d disturbances. 2. Operations. Data from the monitors were reduced to punch card form and a program w r i t t e n f o r analysis of the data by an IBM 704 or 1620 computer. 3. Personnel. This p r o j e c t was supervised by J.A. Lockwood; J.H. Trainor and Mashea were associated w i t h the work. 4. Data. A l l data from Mt. Washington have been submitted to the IGY World Data Centers. 5. Results. From an analysis of data from Mt. Washington, Mt. Norikura, Japan ( f u r - nished thraugh the cooperation of Y. Miyataki) and Huancayo, from 1954 to 1958, the f o l l o w i n g i n t e r p r e t a t i o n has been made of the long-term v a r i a t i o n . The decline over the period from 1954 to 1958, as w e l l as i n the previous solar cycle, was not a slow gradual process, but occurred i n several sudden drops ( p a r t i c u l a r l y Forbush events) from which only p a r t i a l recovery took place. The Forbush events are probably pro- duced by the passage of the earth i n t o a solar gas cloud; and the continued suppres- sion of the g a l a c t i c i n t e n s i t y and charge i n energy spectrum and c u t o f f r i g i d i t i e s a f t e r some of these events would appear to r e s u l t from the e f f e c t s of these same so- l a r clouds or beams. The analysis of the cosmic ray data from the IGY network during the sudden de- crease of February 11, 1958, was completed. I n that event, the unusual r a p i d i t y of the decrease, which was followed by a teiq>orary recovery at s t a t i o n s of magnetic l a - t i t u d e less than 50°, provided a c r i t i c a l t e s t f o r e x i s t i n g s o l a r - c o n t r o l l e d modulat- ing mechanisms. The main decrease, which occurred p r a c t i c a l l y simultaneously over the e arth, was r e l a t i v e l y energy i n s e n s i t i v e . The subsequent temporary recovery ap- peared to be associated w i t h a s p a t i a l anisotropy. I t i s suggested that these v a r i - a tions can be i n t e r p r e t e d as the r e s u l t of disordering of the outer geomagnetic f i e l d by the solar wind as f i r s t pointed out by E.N. Parker. Further analyses of Forbush events led t o the conclusion t h a t the r i g i d i t y depen- dence of the long term v a r i a t i o n does not agree w i t h that c alculated by Parker f o r the e f f e c t of a h e l i o c e n t r i c s h e l l of disordered magnetic f i e l d s i n the presence of the solar wind; the r i g i d i t y dependence determined by t h i s analysis turned out t o be intermediate between the two cases of disordering considered by Parker. And the sa- t e l l i t e observations o f Forbush decreases occurring m i l l i o n s o f miles i n t o space ex- clude any such geocentric modulation mechanism. Hence, one must consider the e f f e c t upon cosmic rays of an ionized solar gas cloud or beam w i t h dimensions comparable t o the earth-sun distance as a miniminn. Of the two models thus f a r proposed, the analysis undertaken here favors the " d i f f u s i v e d e celeration" mechanism proposed by S.F. Singer. The cosmic ray increase of May 4, 1960, which occurred sixteen minutes a f t e r a class 2 solar f l a r e occurred on the west limb, was studied i n conjunction w i t h solar 118
COSMIC RAYS radio noise data and riometer data. I t was found t h a t the d i f f e r e n t i a l r i g i d i t y spec- trum f o r the p a r t i c l e s produced i n t h i s event was not as steep as found f o r the Febru- ary 23, 1956 event. The d i u r n a l v a r i a t i o n analysis i s not completed as y e t . 6. Bibliography. a. Papers Presented at Meetings. J.A. Lockwood: "On the Long-Term V a r i a t i o n i n the Cosmic Radiation" and "Decrease of Cosmic-Ray I n t e n s i t y on February 1, 1958." F o r t y - F i r s t Annual Meeting, American Geophysical Union, A p r i l 1960, Washington, D.C. b. Published Papers. J.A. Lockwood: "Variations i n the Cosmic-Ray Nucleonic I n t e n s i t y . " Phys. Rev., v o l . 112, no. 5, 1958, pp. 1750-58. L.L. Towle, J.A. Lockwood: "Cosmic-Ray Increases Associated w i t h Solar Flares." Phys. Rev., v o l . 113, no. 2, Jan. 15, 1959, pp. 641-647. J.A. Lockwood: "On the Long-Term V a r i a t i o n i n the Cosmic Radiation." JGR. v o l . 65, no. 1, Jan. 1960, pp. 19-25. J.A, Lockwood: "Decrease o f Cosmic-Ray I n t e n s i t y on February 11, 1958." JGR., v o l . 65, no. 1, Jan. 1960, pp. 27-37. J.E. Henkel, J.A. Lockwood, J.H. Trainor: "A Comparison of the Cosmic-Ray I n t e n s i t y at High A l t i t u d e s w i t h the Nucleonic Component at Ground E l e v a t i o n . " JGR, v o l . 64, no. 10, October 1959. pp. 1927-38. J.A. Lockwood: "Variations i n the Cosmic Ray Neutron I n t e n s i t y . " U n i v e r s i t y o f New Hampshire, Physics Dept., F i n a l Report Contract AF 19(604)-1550. J.A. Lockwood: "An I n v e s t i g a t i o n of the Forbush Decreases i n the Cosmic Radiation." JGR, v o l . 65, no. 12, Dec. 1960, pp. 3859-80. J.A. Lockwood: "Increase of the Nucleonic I n t e n s i t y on May 4, 1960." (Accepted f o r p u b l i c a t i o n ) , JGR, v o l . 65, no. 10, 1960. J.A. Lockwood: "Intensity-Time V a r i a t i o n of the Cosmic R a d i a t i o n . " A.J. Phys.. v o l . 30, no. 1, January 1962, pp. 10-15. 119
COSMIC RAYS Project 2.32 - Reduction and Analysis of Cosmic-Ray Data 1. Ob.iectives. This p r o j e c t at the Department of Physics, U n i v e r s i t y of Maryland was set up to provide f o r reduction of data from U. of M. cosmic-ray IGY s t a t i o n s (Wilkes, Thule, Climax, Banff) and f o r analysis of these data i n association w i t h r e - late d geophysical phenomena. 2. Personnel. This work was supervised by S.F. Singer; K. Maeda and V.L. P a t e l were associated w i t h the work. 3. Data. Data from Wilkes and Thule were reduced according to the CSAGI plan and submitted to the IGY World Data Centers. 4. Results. a. Large seasonal v a r i a t i o n s of cosmic-ray i n t e n s i t y i n polar regions were found from the data of Wilkes and Thule telescopes, which were corrected f o r barometric e f - f e c t by the c o e f f i c i e n t s determined by regression analysis. I n t e r p r e t a t i o n of t h i s seasonal v a r i a t i o n by atmospheric temperature e f f e c t s as w e l l as t h e o r e t i c a l explana- t i o n f o r the anormally large values of temperature c o e f f i c i e n t s f o r those polar s t a - t i o n s were discussed and published. b. I n v e s t i g a t i o n of solar f l a r e e f f e c t on the cosmic-ray i n t e n s i t y i n polar r e - gions was performed by making use of Wilkes and Thule data. The r e s u l t s showed a r e - markable f a c t , i n d i c a t i n g the h i g h l y disturbed nature of the i n t e r p l a n e t a r y f i e l d during IGY. This r e s u l t and an i n t e r p r e t a t i o n of the c o n t r o v e r s i a l r e s u l t s of solar f l a r e e f f e c t on cosmic-ray i n t e n s i t y among several i n v e s t i g a t o r s were published. c. From the analyses of high counting rate cosmic-ray data obtained at the moun- t a i n s t a t i o n s (Climax and B a n f f ) , a strong l o c a l time dependence of short period f l u c - t u a t i o n s was detected. Further i n v e s t i g a t i o n s of these r a p i d f l u c t u a t i o n s are s t i l l i n processing. d. On May 4, 1960 a ra p i d increase i n cosmic-ray i n t e n s i t y was observed at v a r i - ous s t a t i o n s i n the world. The rate-meter records at Climax, Banff, and College Park and 15 minute data of mu-meson telescope at Thule gave valuable i n f o r m a t i o n on t h i s event. D e t a i l s are now being published. 5. BiblioRraphy. a. Papers Presented at Meetings. V.L. Patel and K. Maeda: "Seasonal V a r i a t i o n of Cosmic Ray I n t e n s i t y i n Polar Regions." January 27, 1960 Annual Meeting of Am. Phys. Soc. b. Published Papers. V.L. Patel and K. Maeda: "Short-term V a r i a t i o n s i n Meson and Nucleon Compon- ent of Cosmic Rays." JGR. v o l . 66, no. 4, A p r i l 1961. K. Maeda and V.L. Patel: "Note on Solar Flare Cosmic Rays." JGR. v o l . 66, no. 4, A p r i l 1961. K. Maeda and V.L. Pa t e l : "Seasonal Variations of Cosmic Ray I n t e n s i t y i n Polar Regions." JGR, v o l . 66, no. 5, May 1961. S.F. Singer, K. Maeda, and V.L. Patel: "Solar Flare Cosmic Ray on May 4, 1960." JGR, v o l . 66, no. 5, May 1961. 120
COSMIC RAYS Project 2.33 - Cosmic-Ray Tr a j e c t o r y Computation and Study 1. Objectives. At the time t h i s p r o j e c t at the School of Physics, U n i v e r s i t y of Min- nesota, was begun a number of cosmic ray measurements had shown that the cosmic-ray i n t e n s i t y as a f u n c t i o n of p o s i t i o n on the earth's surface was quite d i f f e r e n t from t h a t predicted by a theory which approximated the earth's magnetic f i e l d by that of a magnetic di p o l e . This p r o j e c t was undertaken to see whether these deviations from p r e d i c t i o n were due to the inaccurate model assumed f o r the earth's magnetic f i e l d or whether they i n d i c a t e d a misunderstanding about magnetic f i e l d s i n space. 2. Operations. An e l e c t r o n i c computer was used to c a l c u l a t e a number of o r b i t s or charged p a r t i c l e s using b e t t e r approximations to the earth's f i e l d . 3. Personnel. This work was c a r r i e d out by Paul J. Kellogg, Melvin Schwartz and Robert Tennison. 4. Results. The f i r s t phases of the work were c a r r i e d out using a 15 parameter ap- proximation to the earth's f i e l d . The r e s u l t s showed b e t t e r agreement w i t h cosmic-ray observations than previous c a l c u l a t i o n s , but l e f t some discrepancy. Kellogg then car- r i e d out c a l c u l a t i o n s using a 48 parameter approximation to the earth's magnetic f i e l d which was the best a v a i l a b l e and showed th a t a l l cosmic-ray observations w i t h i n about 15° of the magnetic equator agreed p e r f e c t l y w i t h the r e s u l t s of the c a l c u l a t i o n s . I t proved i m p r a c t i c a l w i t h the computer a v a i l a b l e to compute t r a j e c t o r i e s f o r l a t i - tudes near the earth's magnetic poles. 5. Bibliography. P.J. Kellogg and M. Schwartz: "Theoretical Study of the Cosmic Ray Equator." I I Nuovo Cimento. Serie X, v o l . 13, pp. 761-768, Aug. 1959. P.J. Kellogg: "Calculations of Cosmic-Ray T r a j e c t o r i e s Near the Equator." JGR. v o l . 65, no. 9, Sept. 1960. 121
COSMIC RAYS Project 2.34 - Reduction of Cosmic-Ray I o n i z a t i o n Chamber Data 1. Obiectives. This p r o j e c t at the Department of T e r r e s t r i a l Magnetism, Carnegie I n s t i t u t i o n of Washington, provided f o r s c a l i n g , reduction, and p u b l i c a t i o n of pres- sure corrected b i - h o u r l y values f o r the duration of the ICY (J u l y 1957 to December 1958) from cosmic-ray i o n i z a t i o n chambers at Godhavn and Mexico i n conformity w i t h CSAGI recommendations. I n a d d i t i o n , i t was planned to scale, reduce, and p u b l i s h pressure-corrected data from Godhavn f o r the period January 1951 to July 1957. 2. Operations. Data from the s t a t i o n s involved were c o l l e c t e d at DTM and corrected f o r bursts and barometric pressure. Tables of b i h o u r l y means of departure from b a l - ance, d a i l y means of hourly departures from balance, and b i h o u r l y values of d i u r n a l v a r i a t i o n s i n departure from balance, were prepared. The data f o r Godhavn and f o r Mexico are included i n a Carnegie I n s t i t u t i o n of Washington p u b l i c a t i o n now i n p r i n t (see Bibliography below). 3. Personnel. These tables and reductions were e f f e c t e d by L i s e l o t t e Beach w i t h t e c h n i c a l assistance by S.E. Forbush. 4. Results. The 24-hour and 12-hour waves m cosmic-ray i n t e n s i t y at Cheltenham (Fredericksburg), Huancayo, and Christchurch and t h e i r v a r i a b i l i t y were analyzed s t a - t i s t i c a l l y , using data, corrected f o r pressure, f o r the period 1937-1959 from Compton- Bennett i o n i z a t i o n chambers. The degree of c o r r e l a t i o n between the deviations of yearly mean 24-hour waves (from t h e i r 23-year means) at any two of the s t a t i o n s i s almost as great as can be expected when account i s taken of the noise l e v e l inherent i n the instruments. The deviations of yearly means, from t h e i r 23-year averages, i n - dicate large secular v a r i a t i o n s which may be due to a quasi-systematic 22-year v a r i a - t i o n . The phase di f f e r e n c e between these yearly d e v i a t i o n vectors at Huancayo and Cheltenham (or Christchurch) i s considerably less than that between the average vec- to r s f o r 23 years. The s t a t i s t i c a l r e a l i t y of the 12-hour wave i s d e f i n i t e l y estab- l i s h e d at a l l three s t a t i o n s , although, at least at Huancayo, the average 12-hour wave probably r e s u l t s e n t i r e l y from systematic e r r o r s due to exceedingly small f r i c - t i o n a l e f f e c t s i n the barograph. 5. Bibliography. S.E. Forbush, D. Venkatesan: "Diurnal V a r i a t i o n i n Cosmic-Ray I n t e n s i t y 1937-59, at Cheltenham (Fredericksburg), Huancayo, and Christchurch." JGR, v o l . 65, no. 8, August 1960, pp. 2213-26. L i s e l o t t e Beach, S.E. Forbush: "Cosmic-Ray Results." Res, of the Dept. of Terrest. Magnetism, Carnegie I n s t i t u t i o n of Washington. 122
COSMIC RAYS Project 2.35 - Airborne Neutron Monitor Survey of the Geomagnetic Equator 1. Objectives. This p r o j e c t was work contr i b u t e d t o the IGY program by the A i r Force Cambridge Research Laboratories (AFCRL), and the U n i v e r s i t y of Chicago (sponsored under USAF O f f i c e of S c i e n t i f i c Research and AFCRL c o n t r a c t s ) . The purpose was to obtain crossings of the geomagnetic equator at longitudes spaced around the earth i n order to map the p o s i t i o n of the cosmic-ray minimum. Since the cosmic rays begin to i n t e r a c t w i t h the earth's magnetic f i e l d throughout a large volume at a considerable distance from the earth, some of the nature of the f i e l d i n these remote regions can be deduced. 2. Operations. Through the cooperation of the A i r Force, a nucIconic component mon- i t o r (two detector, Chicago design) was i n s t a l l e d i n a long-range a i r c r a f t and trans- ported at constant pressure a l t i t u d e (approximately 18,000 f e e t ) i n a p a t t e r n of traverses across the equator; twelve traverses were obtained f o r which the data can be analyzed to give the shape of the curve both sides of minimum (see Fig. 8 ) . 3. Personnel. Ludwig Katz, AFCRL, and J.A. Simpson, U n i v e r s i t y of Chicago, were pro- j e c t supervisors. 4. Data. The reduced data were published as part of the papers r e p o r t i n g on t h i s work. Some of the data reduction was c a r r i e d out under a special research p r o j e c t supported by the USNC w i t h funds from the Ford Foundation. 5. Results. The cosmic-ray equator was found t o l i e west of the equator computed from the eccentric d i p o l e approximation of the earth's magnetic f i e l d (see Fig. 9 ) . Agreement i s b e t t e r w i t h the surface dip equator, although i t can be seen that the A t l a n t i c Ocean anomaly i n the v i c i n i t y of 60°W Longitude apparently does not s i g n i f i - c a n t l y a f f e c t the cosmic-ray d e f l e c t i o n . These studies on the cosmic-ray equator, which o r i g i n a t e d at Chicago, have led to worldwide changes i n the geomagnetic c u t - o f f s f o r charged p a r t i c l e s a r r i v i n g at the earth. The work has stimulated many i n v e s t i g a t i o n s both i n the U.S. and Europe. I n a d d i t i o n t o the cosmic-ray equator, the f i r s t d e f i n i t e measurement of the lon- gitude e f f e c t of cosmic r a d i a t i o n at the geomagnetic equator was obtained i n these experiments, which independently show that the magnetic center i s eccentric w i t h r e - spect to the earth's axis of r o t a t i o n . 6. Bibliography. J.A. Simpson: "New Experiments Concerning the Geomagnetic F i e l d Extending i n t o I n t e r p l a n e t a r y Space." Geophys. Monog. No. 2, Geophysics and the ICY, pp. 65-70, Am. Geophys. Union, 1958. L. Katz, P. Meyer, J.A. Simpson: "Further Experiments Concerning the Geomag- net i c F i e l d E f f e c t i v e f o r Cosmic Rays." Nuovo Cimento. Suppl. a l v o l . V I I I , Ser. X, no. 2, 1958. 123
COSMIC RAYS 120 ISO 180 Center Eqtiator Fit for lihasi 30 West 0 Figure 8. Route of A i r c r a f t Carrying Neutron Monitor a t Constant Pressure A l t i t u d e . o30» rto»/v \ / Cosmic Ray Equator Eccentric Dipole Field Equator Dip EquatorCO'lnclination) 1945 Survey â¢c I GEOGRAPHIC LONGITUDE <P ^^^f 'lio^ '9i)o' 'ely' 'all"' ' Ì ' 'sb-' W i8iy -ho»s Figure 9. Comparison of Cosmic Ray, Dipole and Dip Equators. 124
