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X I V NUCLEAR RADIATION PROGRAM F i l t e r and B l o w e r U n i t u s e d f o r Week-long C o l l e c t i o n s o f F i s s i o n P r o d u c t s
NUCLEAR RADIATION PROGRAM Page Organization of Working Group on Nuclear Radiation 543 U.S. Nuclear Radiation Program 543 Program of the Atomic Energy Commission 544 Program of the U.S. Public Health Service 545 Program of the A i r Force Cambridge Research Laboratories 546 Program of the Naval Research Laboratory 547 542
XIV. NUCLEAR RADIATION A. Organization of Working Group on Nuclear Radiation 1. Establishment o f Working Group. When the CSAGI c i r c u l a r i z e d the various IGY p a r t i - c i p a t i n g committees on items f o r discussion f o r the t h i r d general assembly, Brussels, September 1955, a proposal was Included from the Netherlands suggesting t h a t the IGY include a program f o r measurement of r a d i o a c t i v e substances c a r r i e d i n the atmosphere. The o b j e c t i v e was to e s t a b l i s h a reference datum and to use the airborne r a d i o a c t i v e ma t e r i a l s as atmospheric t r a c e r s . An informal ad hoc group met i n June 1955 to prepare a p r e l i m i n a r y assessment of the proposal and of p o t e n t i a l U.S. p a r t i c i p a t i o n ; repre- sentatives o f the AEC, USWB, ONR and NRL attended. At the Brussels meeting o f CSAGI, a c t i o n on the Netherlands proposal was deferred to allow more time f o r the IGY countries to make programmatic studies. At the f o u r t h CSAGI meeting, September, Barcelona, the nuclear r a d i a t i o n program was incorporated i n t o the IGY and a CSAGI working group appointed. A meeting was arranged to be held i n Utrecht i n e a r l y 1957 when s p e c i a l i s t s from i n t e r e s t e d countries would give papers and discuss techniques o f observation and a n a l y s i s . An ad hoc group was convened i n December 1956 to plan U.S. p a r t i c i p a t i o n i n the Utrecht meeting. A f t e r that meeting, where recommendations as to programs and techniques were evolved, a Working Group on Nuclear Radiation was organized under the Technical Panel on Meteorology. 2. Composition of the Working Group. ( A f f i l i a t i o n a t tune o f appointment.) Lester Machta, Chairman J.H. Harley E.A. M a r t e l l H.J.L. Rechen L.B. Lockhart, J r . U.S. Weather Bureau AEC, New York Operations O f f i c e Geophysics Research D i r e c t o r a t e , AFCRL U.S. Public Health Service U.S. Naval Research Laboratory B. U.S. Nuclear Radiation Program The Working Group on Nuclear Radiation held several informal meetings a t which was discussed appropriate e x i s t i n g programs of the Atomic Energy Commission, Public Health Service, Naval Research Laboratories and Geophysics Research D i r e c t o r a t e t h a t could be incorporated i n t o the U.S. program f o r IGY. These programs are described i n the f o l l o w i n g pages. Techniques employed f o r c o l l e c t i n g r a d i o a c t i v e m a t e r i a l included gummed paper deposition (AEC), pot c o l l e c t i o n of p r e c i p i t a t i o n and deposited matter (AEC), and a i r f i l t e r apparatus (NRL, GRD). 543
NUCLEAR RADIATION Program of the Atomic Energy Commission 1. Operations. The New York Operations O f f i c e of the Atomic Energy Commission had two programs f o r c o l l e c t i n g r a d i o a c t i v e m a t e r i a l . One consisted of exposing a one-square- f o o t sheet of gummed cellulose-acetate f i l m on a h o r i z o n t a l surface about three f e e t above the ground. The f i l m was l e f t exposed f o r twenty-four hours, then mailed back to New York f o r counting. Here the f i l m was reduced to ash, placed i n a p l a s t i c planchet and fed through an automatic counting device, where the t o t a l beta a c t i v i t y of the sample was determined. Such c o l l e c t i o n s were made d a i l y a t about 40 st a t i o n s i n the con t i n e n t a l United States and cooperatively a t about 80 st a t i o n s elsewhere i n the world. The second program consisted of continuously exposing a high-walled s t a i n l e s s s t e e l pot 0.82 f t 2 i n area. Each month, the contents of the pot, rinsed w i t h d i s t i l l e d water i f necessary, were b o t t l e d and shipped t o New York f o r analysis of gross f i s s i o n pro- ducts, beta a c t i v i t y and of Strontium-90 content. Such pots were located a t ten s t a t i o n s i n the c o n t i n e n t a l United States and 16 elsewhere i n the world. 2. Personnel. This work was under the supervision of John H. Harley. 3. Bibliography. Health and Safety Laboratory Quarterly Reports-65, May 29, 1959. Health and Safety Laboratory Quarterly Reports-69, October 1, 1959. Health and Safety Laboratory Quarterly Reports-77, January 1, 1960 Health and Safety Laboratory Quarterly Reports-84, A p r i l 1, 1960. Health and Safety Laboratory Quarterly Reports-88, July 1, 1960. Health and Safety Laboratory Quarterly Reports-93, September 5, 1960. Health and Safety Laboratory Quarterly Reports-95, October 1, 1960. 544
NUCLEAR RADIATION Program of the U.S. Public Health Service 1. Operations. The Public Health Service Radiation Surveillance Network, a coopera- t i v e a c t i v i t y w i t h the U.S. Atomic Energy Commission, consisted of about f o r t y f i e l d sampling s t a t i o n s and c e n t r a l laboratory. Three of the f i e l d s t a t i o n s and the c e n t r a l laboratory were operated by the Public Health Service, the remainder of the s t a t i o n s were operated under the supervision of the appropriate State Departments of Health, w i t h operating personnel furnished e i t h e r by the s t a t e s or cooperating l o c a l health departments. Measurement of the concentration of f i s s i o n product a c t i v i t y was iLade by f i l t e r i n g a i r through a four-inch-diameter dust f i l t e r a t a r a t e of about 34 cubic f e e t per min- ute. Two sampling schedules were used: (a) continuous samples of 24 hours duration and (b) approximately 3-1/2 day samples on a t i m e r - c o n t r o l l e d schedule operating one hour out of every three. The s t a t i o n operators estimated the a c t i v i t y on the f i l t e r and then sent i t to the laboratory i n Washington, D.C., f o r counting. The f i l t e r s were measured f o r beta a c t i v i t y w i t h a thin-window, 7 1/2 inch,gas-flow p r o p o r t i o n a l counter. Each sample was counted twice; f i r s t , a t l e a s t three days a f t e r c o l l e c t i o n and then seven days l a t e r . On the basis of these two a c t i v i t y measurements, and assu- ming that the beta a c t i v i t y has decayed by the Way-Wigner formula, the a c t i v i t y was extrapolated back to the time of end of c o l l e c t i o n . P r e c i p i t a t i o n samples were c o l l e c t e d by 20 of the network s t a t i o n s . When p r e c i p i - t a t i o n occurred one sample was taken during each sampling period. The sample was c o l - lected w i t h a funnel 0.4 square meters i n area and a c o l l e c t o r b o t t l e . At the c o l l e c - t i o n s i t e 0.5 l i t e r s of the c o l l e c t e d p r e c i p i t a t i o n was evaporated to dryness i n a rectangular aluminum d i s h , which was sprayed w i t h p l a s t i c , f l a t t e n e d , and mailed to the c e n t r a l laboratory f o r counting. The p r e c i p i t a t i o n samples were counted and the a c t i v i t y extrapolated back to the end of c o l l e c t i o n i n the same manner as f o r the a i r f i l t e r s . 2. Personnel. This work was under the supervision of H.J.L. Rechen. 545
NUCLEAR RADIATION Program of the A i r Force Cambridge Research Laboratories 1, Operations. Several types of samples were c o l l e c t e d f o r the measurement of envi- ronmental r a d i o a c t i v i t y . Fresh p r e c i p i t a t i o n samples from s i x of the networks were ana- lyzed f o r Sr^5, Sr^", Ba^^^, WÌ ", and Pb^lO, Selected p r e c i p i t a t i o n samples were ana- lyzed f o r t r i t i u m . I n d i v i d u a l p r e c i p i t a t i o n samples were obtained from three New England s i t e s and a selected number were analyzed f o r Sr^^, Sr^O, Ba^^O, Wl85^ and Pb^lO. Snow cores and fresh snows from Greenland and the A n t a r c t i c were analyzed f o r Sr^^ and Pb^^^. I n a d d i t i o n , d a i l y surface-air samples were taken a t Bedford, Mass. (42''N, 71''W) w i t h the NRL/IGY system and sent to the Naval Research Laboratory f o r t o t a l beta measurements. A Geophysics Research Di r e c t o r a t e report i s i n preparation and w i l l contain a des- c r i p t i o n of the radiochemical and low-level beta-measurement techniques employed, as w e l l as a t a b u l a t i o n o f , r e s u l t s f o r Sr^^^ Sr^O, Bal^O, Wl85^ and Pb210 assays. 2. Bibliography. C.W. Chagnon: "Balloon Borne A i r Sampling Apparatus." Instrumentation f o r Geophysical Research. No. 6, GRD/AFCRL, Bedford, Mass., A p r i l 1957. P.J. Drevinsky, C.E. Junge, I.H. B l i f f o r d , J r . , E.A. M a r t e l l , M.I. K a l k s t e i n , "Natural aerosols and nuclear debris studies". Geophysics Research D i r e c t o r a t e Notes No. 8 (1958). M.I. K a l k s t e i n , P.J. Drevinsky, E.A. M a r t e l l , C.W. Chagnon, J.E. Manson, C.E. Junge: "Natural aerosols and nuclear debris studies". Geophysics Research Directorate Notes, No. 24 (1959). E.A. M a r t e l l : Science 129, 1197 (1959). E.A. M a r t e l l and P.J. Drevinsky, Science JJ2, 1523 (1960). 546
NUCLEAR RADIATION Program of the Naval Research Laboratory 1. Operations. The program of the Naval Research Laboratory consisted of a network of twenty-one s t a t i o n s extending along the 80'W meridian from Thule, Greenland, to Punta Arenas, C h i l e , making d a i l y a i r - f i l t e r c o l l e c t i o n s through cooperative agreements w i t h various governments and agencies to c o l l e c t samples. I n a d d i t i o n , a t four s t a t i o n s elsewhere, weekly a i r - f i l t e r c o l l e c t i o n s were made, and a complete a i r monitor u n i t was i n operation a t L i t t l e America, A n t a r c t i c a . Similar monitor s t a t i o n s were i n operation a t Kodiak and Wales, Alaska, and a t Yokosuka, Japan, but were not o f f i c i a l l y p a rt of the IGY program. Each s t a t i o n where d a i l y c o l l e c t i o n s were made was equipped w i t h an NRL/IGY system co n s i s t i n g of a positive-displacement a i r pump driven by a constant-speed e l e c t r i c motor w i t h a flow- r a t e of about 30 cubic feet per minute through an 8-inch diameter f i l t e r paper. F i l t e r s were changed each morning and forwarded to the U.S. Naval Research Laboratory i n Washington, where they were ashed a t 650°C., compressed to a t h i n wafer, and counted w i t h a thin-window,halogen-filled Geiger tube. Each sample was counted 14 days a f t e r c o l l e c t i o n . Weekly c o l l e c t i o n s a t other s t a t i o n s were made by a larger f i l t e r (17x13 inches) a t a flow r a t e of 35 cubic feet per minute. Monthly composites of i n d i v i d u a l samples from each s t a t i o n were analyzed f o r the fo l l o w i n g radioisotopes: Sr89, Sr^O, y ^ l , Csl37^ C e l ^ l , Cel^^, wl85^ ^nd Pb210. The equipment a t L i t t l e America c o l l e c t e d the p a r t i c u l a t e matter from about 1000m3 of a i r over a 24-hour period, then on-site measurements of the r a t e of decay were made so t h a t information on n a t u r a l r a d i o a c t i v i t y as w e l l as f i s s i o n product a c t i v i t y was a v a i l a b l e . This equipment was i d e n t i c a l t o the NRL a i r monitors operated since 1950 at several s i t e s i n the Northern Hemisphere, wherein a i r was drawn through an intake about 40 fe e t above ground l e v e l and the airborne p a r t i c u l a t e matter c o l l e c t e d on a f i l t e r apper (U.S. Army Chemical Corps, type 5) 2 inches m diameter. A t the l i n e a r flow r a t e employed, equivalent to an i n i t i a l volume of approximately 30 CFM, the mea- sured r e t e n t i v e e f f i c i e n c y of the f i l t e r was 100 per cent f o r one micron and b e t t e r than 95 per cent f o r 0.3 micron p a r t i c l e s . A f t e r twenty-four hours continuous exposure, the sample was tr a n s f e r r e d t o a lead ju g and i t s b e t a - a c t i v i t y followed f o r 16 hours using a h a l o g e n - f i l l e d end-window Geiger tube. From the r a t i o of the 6th-hour to the 16th-hour count, the l o n g - l i v e d contaminant ( p r i n c i p a l l y f i s s i o n products since the lo n g - l i v e d n a t u r a l beta emitters had been found to c o n t r i b u t e a n e g l i g i b l e amount o f a c t i v i t y ) o f the r e s i d u a l 10.6- hour ThB a c t i v i t y was determined. The two d i f f e r e n t techniques described above led to divergent values. Analysis o f the various factors involved i n the two methods led to the conclusion t h a t differences were a t t r i b u t a b l e to the changing energy d i s t r i b u t i o n of the f i s s i o n product conglomer- ate w i t h age. The knowledge o f the magnitude o f t h i s change and i t s e f f e c t on the standardization and counting procedures was f e l t to be necessary to the i n t e r p r e t a t i o n of gross f i s s i o n product concentrations as determined by the various independent methods. Standardization o f counting equipment toward gross f i s s i o n product mixtures i s thus a d i f f i c u l t problem. A l l present a i r monitor networks, and presumably a l l systems sampling gross f i s s i o n product a c t i v i t y , s u f f e r inherent inaccuracies due to t h i s pro- blem. Rough c a l c u l a t i o n s i n d i c a t e t h a t the NRL/IGY system gives a reasonably accurate accounting of the t o t a l f i s s i o n products having P max. energies exceeding 0.2 Mev. This system tends to underestimate the qu a n t i t y of fresh debris i n the a i r because of the c a l i b r a t i o n method employed and also because of the loss of v o l a t i l e f i s s i o n pro- ducts during ashing and through r a d i o a c t i v e decay during the 14-day cooling o f f period. For f i s s i o n products over s i x months of age, the r e s u l t s are f e l t t o be w i t h i n 10 per cent of the correct value. 547
NUCLEAR RADIATION The NRL monitor system gives r e s u l t s which are c o n s i s t e n t l y low due to the method of c a l i b r a t i o n , moreover, t h i s e r r o r tends to increase as the f i s s i o n debris age and may be as much as 25-30 per cent low f o r year-old u235 f i s s i o n debris. For actual f i s s i o n product mixtures presently i n the a i r , the r e s u l t s may be low by 50 per cent. Measurement of the gross a c t i v i t y l e v e l s serves to give a quick and r e l a t i v e l y simple procedure f o r f o l l o w i n g the short term changes i n the a i r concentration o f f i s s i o n products, and thus the r e l a t i v e day-to-day a c t i v i t y l e v e l s can be determined roughly without any r e l a t i o n to the t o t a l number of f i s s i o n s c o n t r i b u t i n g t o the gross a c t i v i t y . While the gross a c t i v i t y gives a q u a l i t a t i v e measure of the f i s s i o n debris i n the a i r , the accurate determination of the i n d i v i d u a l radioisotopes c o n t r i b u t i n g to the t o t a l a c t i v i t y i s necessary to obtain unambiguous information. The continuing program of measuring f i s s i o n product r a d i o a c t i v i t y m the ground- l e v e l a i r a t s i t e s along the 80th meridian (west) has supplied information on radio- a c t i v i t y dating back to 1956 i n some cases and extending through the IGY and IGC-1959 up to the present. P r i o r t o the cessation of nuclear t e s t i n g i n November 1958, gross a c t i v i t y l e v e l s a t the various s i t e s could be r e l a t e d to s p e c i f i c t e s t series; since th a t tune d e f i n i t e evidence of spring maxima i n stratospheric deposition has been found i n the Northern Hemisphere. Radiochemical analyses of c o l l e c t i o n s f o r s p e c i f i c isotopes has permitted the be t t e r i d e n t i f i c a t i o n of the sources of these f i s s i o n products. The spreading of debris from the U.S. Hardtack t e s t s , f o r example, was traced by means of Wl85 a c t i v i t y produced uniquely m t h i s series; the younger debris from the USSR tests of Oct-Nov 1958 were i d e n t i f i e d by isotope r a t i o s i n v o l v i n g some of the s h o r t e r - l i v e d isotopes. I t has become obvious that r a d i o a c t i v e debris are not necessarily r e s t r i c t e d to a narrow l a t i t u d e band w i t h i n the troposphere; furthermore, s u b s t a n t i a l cross-over of debris from the Northern and Southern Hemisphere i s possible, on occasion. Mixing w i t h i n the troposphere i s , generally, a much fa s t e r process than mixing w i t h i n the stratosphere above e i t h e r hemisphere or across the equator. Current studies are con- cerned w i t h the r a t e of e q u i l i b r a t i o n of the stratospheric burden above the Northern and Southern Hemispheres and the r a t e of depletion of t h i s source. 2. Personnel. This work was under the d i r e c t i o n of L.B. Lockhart, J r . 3. Bibliography. L.B. Lockhart, J r . , R.A. Baus, and I.H. B l i f f o r d , J r . : "Fission Product R a d i o a c t i v i t y i n the A i r along the 80th Meridian-January-June 1957". Tellus X I , No. 1, 1959. (NRL Report 5041, November 27, 1957). L.B. Lockhart, J r . , R.A. Baus, P. King, and I.H. B l i f f o r d , J r . : "Atmospheric R a d i o a c t i v i t y Studies a t the U.S. Naval Research Laboratory". (NRL Report 5249, December 19, 1958) . R.A. Baus, R.L. Patterson, J r . , A.W. Saunders, J r . , and L.B. Lockhart, J r . : "Radiochemical Analyses of A i r - f i l t e r Samples Collected During 1957". (NRL Report 5239, December 31, 1958). L.B. Lockhart, J r . , and Peter King: "Speculations on Atmospheric Processes Via Fission Product Levels". American S c i e n t i s t , Vol. 47, No. 3, September 1959. L.B. Lockhart, J r . : "Atmospheric R a d i o a c t i v i t y Levels a t Yokosuka, Japan, 1954-1958". (NRL Report 5301, A p r i l 21, 1959). 548
NUCLEAR RADIATION L.B. Lockhart, J r . , R.L. Patterson, J r . , and W.L. Anderson; "Measurements o f the A i r Concentration o f Gross F i s s i o n Product R a d i o a c t i v i t y During the IGY, July 1957-December 1958". (NRL Report 5359, September 18, 1959). L.B. Lockhart, J r . , R.A. Baus, R.L. Patterson, J r . , and A.W. Saunders, J r . : "Radiochemical Analyses of A i r - F i l t e r Samples Collected During 1958". (NRL Report 5390, October 23, 1959). L.B. Lockhart, J r . , and R.L. Patterson, J r . : " C r i t i c a l Analysis of Measurements of the Gross F i s s i o n Product A c t i v i t y i n the A i r at Ground Level". (NRL Report 5440, February 19, 1960). L.B. Lockhart, J r . , R.A. Baus, R.L. Patterson, J r . , and A.W. Saunders, J r . : "Radiochemical Analyses of F i s s i o n Debris i n the A i r along the 80th Meridian, West". (Journal of Geophysical Research, Vol. 65, No. 6, June 1960). L.B. Lockhart, J r . , R.A. Baus, R.L. Patterson, J r . , and A.W. Saunders, J r . : "Contribution of Hardtack Debris t o Contamination of the A i r during 1959". (Science, Vol. 132, No. 3420, Ju l y 15, 1960) . L.B. Lockhart, J r . , R.L. Patterson, J r . , A.W. Saunders, J r . , and R.W. Black: "Fission Product R a d i o a c t i v i t y i n the A i r Along the 80th Meridian (West) During 1959". (NRL Report 5528, August 15, 1960). L.B. Lockhart, J r . : "Atmospheric R a d i o a c t i v i t y i n South America and A n t a r t i c a " . (NRL Report 5526, August 15, 1960). L.B. Lockhart, J r . , and R.L. Patterson, J r . : "Char a c t e r i s t i c s of A i r F i l t e r Media Used f o r Monitoring Airborne R a d i o a c t i v i t y " . (NRL Report 6054, March 20, 1964). I n a d d i t i o n , summaries o f the NRL network data are a v a i l a b l e i n various NRL re p o r t s . 549
