30lufi*48 
 
 MDDC - 10U8 
 
 TOUTED STATES 
 
 atomic energt com-hssion 
 oae: eidge 
 
 TEMESSEE 
 
 FISSION OE BI-SI'IUTH, LE^D, THALLIUM, PLATHTCM 
 Alff) T.'mTALUM /OrrH HIGE ENERGY P.-VPTICLES 
 
 I. Perlnan 
 
 3. H. Goeckermaxm 
 
 D. H. Templeton 
 
 J. J. Howleaid 
 
 University of California 
 
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 Document Declassified: June 12, 19^7 
 This document consists of \ pages 
 
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1,'DDC - 1048 
 
 Fission of Bismuth, Lead, Thallium, Platinum 
 and Tantalum with High Energy Particles 
 
 I. Perlman, R. H. Goeokerraann, D. H. Templeton and J. J. Rowland 
 Radiation Laboratory and Department of Chemistry 
 University of California, Berkeley, California 
 
 May 16, 1947 f^-. ttie Atomic Energy CoamiisDion <fc-^-' -/^ 
 
 iieciaesification Officer JJ^^ 
 The 134 -inch Berkeley frequency -modulated cyclotron produces 
 
 deuterons, helium ions and neutrons of energies up to 200, 400, and 100 
 
 Mev respectively. Nuclear fission in elements covering the range of 
 
 atomic numbers 83 (bismuth) to 73 (tantalum) has been observer' with one 
 
 or more of the above projectiles. Fission was determined by chemical 
 
 identification of radioactive fission products. 
 
 Although a number of the fission products characteristic of slow 
 
 neutron fission of uranium are found, the fission reaction on these 
 
 light elements with high energy particles differs in some important 
 
 respects. There is no evidence for well-defined assymetric cleavage 
 
 with a deep valley at the midpoint of the yield curve as is the case 
 
 with slow neutron fission; Another difference is the appearance in 
 
 good yield of light isotopes of a given element, and undoubtedly the 
 
 formation of stable isotopes as primary fission products is not 
 
 unusual. For example, the shielded isotope Br^^ is formed in comparaHs 
 
 yield to Br^" with 400 Mev helium ions and 200 Mev deuterons on 
 
 bismuth while the relative yields are 1 to 10* for these isotopes in 
 
 (1) 
 the slow neutron fission of uranium. In -the bombardment of bismuth 
 
 and lead with 400 Mev helium ions no measurable amount of Ba^*° 
 
 (formed in highest yield with slow neutrons on uranium) was found 
 
 - 1 - 
 
- 2 - 1/,DDC - 10/t8 
 
 (2) 
 but an activity which is probably Ba^"" was noted. This Isotope is 
 
 not found at all in the fission of uranium with slov/ neutrons as it 
 
 falls well down among the lightest stable isotopes of barium. 
 
 It has not been possible, thus far, to compare accurately yields 
 from different bombardments because of the inability to determine the 
 beam strength. However, certain trends appear to be definite: The 
 probability of the fission reaction for a given projectile drops off 
 as the target atomic number decreases from bismuth to tantalum. That 
 for a given target element the fission yield decreases as the projec- 
 tile energy decreases is indicated by the decrease in yield of bromine 
 activities from bismuth fission as the deuteron energy is varied from 
 200 to 50 Mev. The distribution of fission products changes in varying 
 the projectile energy since the ratio of Br to Br ' was 2 for 200 
 Mev deuteron on bismuth and 100 for 50 Mev deuterons on bismuth. 
 
 Table 1 shows fission products found from the reaction of 400 
 
 Mev helium ions with bismuth and the relative yields of these isotopes. 
 
 The radioactive properties checked reasonably well those previously 
 
 (1,2) 
 reported for these isotopes. The yields are expressed in 
 
 arbitrary units. It is of interest that Ba"° was not present in 
 
 detectable amount. 
 
- 3 - 
 
 Table 1 
 
 MDDC - loyts 
 
 Relative Yields of Fission Products 
 from 400 Mev Helium Ions on Bismuth 
 
 Ga 
 
 7e 
 
 Br 
 
 S2 
 
 Br 
 
 Sr 
 
 80 
 
 9 1 
 
 r90 
 
 
 22 
 
 150 
 
 390 
 
 54 
 
 1400 
 
 Mo»« 
 
 480 
 
 Ru^°^ , Rhi°6 
 
 240 
 
 jioi 
 
 8 
 
 Baiso 
 
 34' 
 
 The conditions of irradiation that were tried and under which 
 fission was observed in all cases are summarized in Table 2. 
 
 Table 2 
 
 Summary of Irradiations in which Fission was Observed 
 
 Target 
 
 Projectile 
 
 Energy CMev) 
 
 Bl 
 
 a 
 
 400 
 
 Bl 
 
 d 
 
 200,150,90,70,50 
 
 Bl 
 
 n 
 
 100 
 
 Pb 
 
 a 
 
 400 
 
 Fb 
 
 d 
 
 200 
 
 Pb 
 
 n 
 
 100 
 
 Tl 
 
 a 
 
 400 
 
 Tl 
 
 d 
 
 200 
 
 Pt 
 
 a 
 
 400 
 
 Ta 
 
 a 
 
 400 
 
- 4 - W>DC - low 
 
 It is of interest to -speculate on the mechanism of the fission 
 
 In view of the high degree of excitation of the compound nucleus. 
 
 Since the probability of fission would increase with a greater charge/ 
 
 (3) 
 mass ratio and since it is known that large numbers of neutrons may 
 
 be ejected from such highly excited nuclei, it seems likely that the 
 actual fission reaction is preceded, on the average, by fthe boiling- 
 off of a large n\imber of neutrons. Some experimental evidence sup- 
 porting this view is the appearance of light isotopes for a given 
 element in a few cases and the finding that the most probable fission 
 results in products the sum of whose masses lies well below that of 
 the target mass number. However, the same observations would result 
 If the fission reaction would occur first with the fragments still in 
 highly excited states after dissipation of their kinetic energy. 
 
 The co-operation of Prof. R. L. Thornton, Dr. D. C. Sewell and 
 all those whose operation of the 184-inch cyclotron made these irradia- 
 tions possible is gratefully acknov/ledged . We wish to thank 
 Professor E. 0. Lawrence for continued interest and Professor G. T. , 
 Seaborg for helpful discussions regarding this work. 
 
 1) Plutonium Project compilation of nuclei formed in fission. 
 J. Am. Chem. Soc. 68, 2411(1946). 
 
 2) G. T. Seaborg "Table of Isotopes" , Rev. Mod. Phys . 16_, l(l944) 
 
 3) B. B. Cunningham, H. H. Hopkins, >M. Lindner, D. R. Miller, 
 
 P. R. O'Connor, I. Pcrlman, G. T. Seaborg and R. C. Thompson, 
 Paper to be given before Stanford University meeting of the 
 American Physical Society, July 11-12, 1947. 
 
UNIVERSITY OF FlORIDA 
 
 3 1262 08909 7512