U, Th and Pu 
duplicate results were about equally 
reliable, these were averaged, as indi- 
cated in the references to the tables. 
When one value was considered supe- 
rior to the others, only that one was 
selected. No attempt was made to 
correct any of the values for the trans- 
fer of yield from one mass chain to the 
next lower one by delayed-neutron 
emission. However, all of the yields 
have been corrected for known per- 
turbations resulting from neutron cap- 
ture by the fission products. 
It has been shown (8, 4) in studies of 
nuclear-charge distribution in fission 
that in most cases the last two or three 
members of a fission-product chain are 
formed almost exclusively from decay 
of precursors. In general, only small 
fractions of the yields of the last two 
members result from direct formation 
as primary fission fragments. There- 
P yr and Pu?” 
Neutron Data 
1—Graphs of Fission Yields 
2—Tables of Fission Yields 
3—Tables of U*** Decay Chains and Yields 
fore a fission yield measured for any of 
the later members of a chain usually 
represents the total yield of that chain. 
In a few cases this rule is violated. For 
example, the total U?*® thermal-neu- 
tron-fission yield of 86-sec I'** is 3.1% 
(Table 2), but the yield for the entire 
mass-136 chain is 6.46%. The differ- 
ence (6.46% — 3.1%) is accounted for 
by some direct formation in fission of 
the next chain member, stable Xe'?*, 
Occasionally the fission yield of a 
product is lower than that of the corre- 
sponding total chain yield because of 
chain branching to isomers. For exam- 
ple, the total yield of Rb** and of total 
mass 85 is 1.30% (Table 2), but the 
yield of 10.3-yr Kr®* is only 0.293%. 
The difference (1.30—-0.293%) repre- 
sents the yield of the isomeric 4.4-hr 
Kr**™, In some cases, differences be- 
tween values for different fission prod- 
ucts within a chain are due to experi- 
mental error. 
The thermal-neutron-fission yields of 
nearly all shielded nuclides are ex- 
tremely low because these nuclides can- 
not result from decay of neutron-rich 
precursors (3, 4). The yields (5) for 
36-hr Br8?, 19-day Rb**, 23-hr Nb%, 
25-min I'?8 and 12.6-hr I'*° from U?35 
fission are all about 3 X 10-° to 5 X 
10-*%. The yields (5) of 13-day Cs!36 
are somewhat larger: 0.006 % from U5, 
0.05% from Pu®*® and 0.12% from 
U3, All attempts to detect radio- 
active products that might result from 
ternary fission, such as 53-day Be’, 
3 X 10%yr Be!®, 87-day S*5, 4.8-day 
Ca‘? and 46-day Fe, have failed (6). 
The upper limits range from 1 X 10-§% 
to 4 X 10-'%. The only well estab- 
lished ternary fission product is He‘, 
which has been observed as an a-parti- 
Th*? and U** . . 
Se 
= 
Wi 
Fission Yield (%) 
a 
| TI 
8 
= 
is 
Fission Yield (%) 
(S) 
8 
meen 
aa 
== 
leet 
ies 
ae 
ie] 
SS 
tI 
el 
=n 
Es 
= 
.000! 
ae 80 90 
100 110 
Mass Number 
120 
130 140 15 
0.000! 
co) 
a 
° 
70 80 90 
100 lO 120 
Mass Number 
130 140 150 160 
237 
