Neutrons From Alpha Emitters (1948) / Chapter Skim
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Pages 22-42
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From page 27... ...
8 The results of both Demers and Richards for Po a-Be have been plotted in Figure 6 in order to indicate the general validity of the data. These plots were obtained from the observed proton energy distribution by taking into account the variation of the neutron-proton scattering cross section with energy.
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(8E61) E>7' p91 (90S Aoy ‘901g ‘absalg ‘1 ‘uoISSIW®a UOJINeU puD DWWDBH 10)
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9 hydrogen-filled cloud chamber. According to Auger, the intensity of the low energy group increases markealy when the more energetic alpha particles of Ra C' or of Th C' are used.
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10 In this way, one obtains r2 = 378 cm4, a value much higher than that observed. This is a strong indication that there is a low energy group of neutrons.
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1} MBe neutrons/sec/g Ra Mp. + MpaBr Yield = 2.7 x 20?
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12 TABLE V Neutron Yields -- Radium on Thick Beryllium Alpha Emitter E, - Mev Neutrons/ 10° alphas Ra 4.791 55 Rn 5.486 90 Ra A 5.998 120 Ra C' 7.680 200 Ra F 5.298 80 According to Table V, the yield of a Po a-Be source should be about 3 x 10° neutrons per second per curie, and of the Rn a-Be, 15 x 106 neutrons per second per curie. The use of radon instead of radium has been rather widespread.
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13 Ra a-B Neutron Source Sources made of mixtures of radium and boron (or polonium and boron) have been used occasionally to obtain lower and more homogenous neutron energies than is obtainable from Ra a-Be.
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From page 41... ...
14 thermal neutrons in a large water tank with that from a standard Ra a-Be source. Thus, the yield of mixed Ra a-B sources may be written: Yield = 6.8 x 106 Mp My + MpaBr2 In the case of boron, Stuhlinger's excitation curve is in fairly good agree- ment with this result and Roberts' yield for polonium alphas, This is an indication that an important low energy neutron group is not present in this case.
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