tions: Initial radiation and residual radiation.
The residual radiation may include radi-
ation from both fallout and neutron-induced activity.
1.3.1 Initial-Gamma Radiation. For a fission-type device the initial radiations are
divided approximately as shown in Table 1.1 (from Reference 5). The major contribution
to initial-gamma radiation is from the fission-product gammas and the gammaradiation
from neutron capture by nN‘ (n, y) in the high-explosive components and air. The prompt
gammas are nearly all absorbed in the device itself and are of little significance outside
of the device.
The fission-product gammas predominate at close distances (Reference 5).
The N44 (n, y) gammas becoine relatively more important at greater distances, and eventually become the major contributor. This applies only to devices with yields of less
than 100 kt, in which the hydrodynamic effect is small. Figure 1.1 shows the contribution
TABLE 1.1
ENERGY PARTITION IN FISSION
.
Mechanism
Percent of Total
.
os
t Fission Energy ¢
|
|
Kinetic Energy of
Fission Fragments
“
pet
(
81.0
5
Total Energy
ne
per Fission
if
a
Mev
162.0
Prompt Neutrons
4.0
Prompt Gammas*
4.0
|
8.0
Fission Product Gammas
2.7
|
5.4
Fission Product Betas
|
2.7
Fission Product Neutrinos
Delayed Neutrons
Totals
* Mostly absorbed in the device.
8.0
\
aaa
5.4
5.5
|
11.0
0.1
|
0.2
100.0
{
200.0
“F
from fission-product gammas and N'4 (n, y) for a one-kt surface burst.
With respect to
time, the nié (n, y) radiation is essentiaily emitted within 0.2 second; the fission-product
gamiras, however, continue to contribute for the first 30 seconds.
For thermonuclear devices, in addition to gamma radiation from fission-product
gammas, it is necessary to consider the interaction of neutrons from the fusion process
with N'4, The radiation due to the fusion process may vary over wide limits, depending
on the design’of the device. For a given yield, the number of neutrons available may be
ten times ‘as great for fusion as for fission, and therefore a large contribution to gammaradiation exposure may be due to the N'* (n, y) reaction in a thermonuclear device (Reference 3).
1.3.2 Residual-Gamma Radiation. Residual-gamma radiation consists of fission~
product radiation from fallout and radiation from neutron-induced activity. The decay
rate of the residual radiation from fallout will follow approximately the expressions:
Ty
and:
= 1,¢7t
ty
r=f I_ dt = 51, (tt, 7%? —t, 7-4)
tt
(1.1)
14