There are many uncertainties in these estimates.
For example, the 80 percent
local fallout from surface bursts is primarily based on very incomplete monitoring data for the Castle Bravo shot, and even if the distribution of total
fallout of gross fission products were known, the question of fractionation
of the Sr-90 remains unsolved.
There is uncertainty concerning the fraction
of debris from large shots which remainsin the troposphere, with evidence
that it is as much as 5 percent.
Another uncertainty is the yield and condi-
tions of firing of the USSR tests. With all these uncertainties, it is obvious that direct sampling is needed to determine the actual Sr-90 content
of the stratosphere.
Table 1
Estimated Stratosphes55 anjections
(after Libby(2))
Mm
1.0
1952
Fall
1954
Spring
1955
Fall
1.2
1956
Summer
5.5
Fall
3.0
Spring
3.0
1957
Fall
4.5
Winter
3-3
Spring
h.o
Fall
1958
19.5
Fall
1.5
20.0
NAG
III.
Other measurements
The reservoir of radioactive debris in the stratosphere has been estab-
lished by direct measurement, at least in the lower stratosphere, by several
investigators prior to the establishment of the AEC balloon sampling program.
However, these earlier techniques were confined to total activity measurements
rather than to the determination of specific isotopes. In 1954 and early
Roe
TE Ste une
ME Ar aad OF TRE
WATIONAL ACA SAbd CF SCIENCES