tions: Initial radiation and residual radiation. The residual radiation may include radiation 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 n‘4 (n, y) in the high-explosive components and air. The prompt
gammas are nearly all absorbed in the device itself and are oflittle significance outside
of the device.
The fission-product gammas predominate at close distances (Reference 5).
The'N'* (n, y) gammasbecoine relatively more important at greater distances, and even-
tually become the major contributor.
This applies only to devices with yields of less
than 100 kt, in which the hydrodynamic effect is small.
’ TABLE 1.1
Figure 1.1 shows the contribution
ENERGY PARTITION IN FISSION
(NNeansare
Percent of Total|
- o.
Fission Energy¢
Mechanism
Kinetic Energy of
Fission Fragments
“4
pet
((
81.0
4
Total Energy
.
per Fission
i
4
Mev
162.0
Prompt Neutrons
4.0
8.0
Prompt Gammas*
4.0
8.0
Fission Product Gammas
|
2.7
|
5.4
Fission Product Betas
2.7
5.4
Fission Product Neutrinos
5.5
11.0
Delayed Neutrons
0.1
100.0
Totals
* Mostly absorbed in the device.
aed
|
\
_
__ 9.2
200.0
~s
from fission-product gammas and nid (n, y) for a cne-kt surface burst.
With respect to
time, the n‘4 (m, y) radiation is essentially emitted within 0.2 second; the fission-product
gamiras, however, continue to contribute for the first 36 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'4 in, y) reaction in a thermonuclear device (Ref-
erence 3).
1.3.2 Residual-GammaRadiation. Residual-gamma radiation consists of fissionproduct radiation from fallout and radiation from neutron-induced activity. The decay
rate of the residual radiation from fallout will follow approximately the expressions:
It = 1,t7t?
and:
te
r =f Ig dt = 51, y7? —t, 7%?)
ty
(1.2)
14