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ATOMIC ENERGY COMMISSION
FISSION OF BISMUTH, LEAD, THALLIUM, PLATINUM
AID TANTALUM WITH HIGH ENERGY PARTICLES
R. H. Goeckermann
D. H. Templeton
J. J. Howland
University of California
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Document Declassified: June 12, 1947
his document consists of 4 pages
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.. *', *<
Fission of Bismuth, Lead, Thallium, Platinum
and Tantalum with High Energy Particles
I. Perlman, R. H. Goeckermann, D. H. Templeton and J. J. Howland
Radiation Laboratory and Department of Chemistry
University of California, Berkeley, California
CLASSi ICATiOi CA,.ELL.ED
Hay 16, 1947 For tne Atomic Energy Commiscson 6-/-Y7
The 184-inch Berkeley frequency-modulated cyclotron produces
deuterons, helium ions and neutrons of energies up to 200, 400, and 100
Nev 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 Bre8 is formed in comparefl
yield to Brse with 400 Mev helium ions and 200 Mev deuterons on
bismuth while the relative yields are 1 to 10' for these isotopes in
the slow neutron fission of uranium. In .the bombardment of bismuth
and lead with 400 Mev helium ions no measurable amount of Ba'O4
(formed in highest yield with slow neutrons on uranium) was found
but an activity which is probably Ba1ss was noted. This isotope is
not found at all in the fission of uranium with slow 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 Bre to Bro 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
reported for these isotopes. The yields are expressed in
arbitrary units. It is of interest that Balo0 was not present in
;: f ^f;
- 2 -
Relative Yields of Fission Products
from 400 Nev Helium Ions on Bismuth
Sre 1 ye
The conditions of
fission was observed in
irradiation that were tried and under which
all cases are summarized in Table 2.
Summary of Irradiations in which Fission
It is of interest to 4epeculate 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/
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 the boiling-
off of a large number 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 acknowledged. 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 Ifotopos" Rev. Mod. Phys. 16. 1(1944)
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.
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