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Fig. 6—Percent of total activity initially injected in the troposphere
as a function of total yield for air bursts in a tropical atmosphere.
The most critical uncertainty in the estimates is for the range of
yields from about 700 kt to about 5 Mt, where the radiological cloud
base may lie in the vicinity of the tropopause. For yields less than 700
kt, the tropospheric fraction (at cloud stabilization) can be estimated to
within a factor of 2 or less. For yields above about 5 Mt, the fraction
in the troposphere becomes very small, although precisely how small
it may be has not yet been determined.
An eStimate of the kiloton equivalent of fission products stabilized
in the troposphere as a function of total yield for air bursts is shown in
Fig. 7. The typical and maximum curves are derived from the curves
in Fig. 6, based on the assumption that the yield is entirely due to fission. Several interesting features may be noted. The maximum tropo-
spheric contamination is produced by bursts in the low megaton range
(assuming 100% fission yield), With typical cloud heights and an aver-
age tropopause height of 54,000 ft, the maximum tropospheric con-
tamination is about 500 kt for yields between about 800 kt and 2 Mt. As
the yield increases, the tropospheric debris decreases rapidly and then
levels off at about 5kt of fission equivalent for yields from 10 to 100 Mt.
The maximum curve, based on a high tropopause and low cloud heights,
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