-lee
il.
.
UCRL-3087
DisCUSSION OF RESULTS
The data (Figs. 1 and 2 and Tables ] and Il) show jeatures reported by
previous author et 2, 3-13
As the pomoarding energy increases, modes oi
fission that a.:e¢ extremely improbable in iow-energy-induced tission pecome
increasingly in.portant.
This results in an increase oi fission yield lor
species tori.ed by syn.metric fission and tor extremely asymn:etiic fission,
as well as increased d.icect iormation of species near or even.on the light
mass side al the peta-stabdility region.
In Grawing smooth curves through the observed iission yield values,
an interesting phenou.enon we.s observed.
Below 50-Mev psroton or deuteron
enerpy the curves are symmetrical in all respects.
they are very delinitely not syn.n.etrical,
Above 50 Mev, however,
Rerlection of the heavy rare-earth
cross sections through the "apparent center oi the tission yield curve" as
estimated i:om: higher-yieid products gives points that fall well below the
oose-ved values on the iow-n.ate-number wing oi the curve.
hand,
‘On the othe:
reiiect.on oc: the low-n.ass-number cross sections through the same
“apparent center"!
earth vaiues.
mass
A
gives poiits that cali above the observed rare-
The higher the enerpy ol the bombarding particle, the more
pronounced the eftect.
Tne cross sections ot Cae!
and
Ni”
+
with 340-Mev
protons, ior example, must be adjusted downwarc oy at least an order oi
Magnituae, os those oi Eu! °°
and
E,)??
adjusted upward by factors ol
fron. three to seven, in order to tall on a curve symmetric about a single A.
.
lob
27
;
eu.
Duplicate runs oi Eu
and
Eu
cross sections showed agreen.ent within
.
five percent while the cross sections of
dent investigations. .
67
e
and
66
Ni
.
;
were from indepen-
The eriect zs certainly outside of experimental error.
The phenon-enon desciiped above might conceivably come about ira
t
€b81005
f
Cu
Major portion oi the independent yields o1 the rare-earth nuclides arose
from: disect forn.ation either as stable 1s0topes o: on the neutron-deticient
side of stapvility.
lL the primary tission products of mass 126, for instance,
were distr:buted so that 72-80". of the mass yield jay in the region
R.
where
W. Spence and G. P. Ford, Ann. Rev. Nuclear Sei. 2, 399 (1953).
10 kK.
H. Goeckern.ann and 1. Perin.an,
i P.
R. ©'Conno: anc G, 1. Seaborg,
he R.
L.
Folger,
P.
C.
Stevenson,
Phys. Rev. 726, 628 (1949),
Phys. Kev. Z7$,
and G.
E » M. Douthett and D. H. Tempietonu,
=
—
1184 (19458). .
T. Seavory,
Phys. Rev. 94,
Phys. Rev. 98, 107(1J 2).
128 (1954).