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Fig. 9—Soil data, 1956: ©, electroanalysis x 1.15; x, HCl extraction.
Nevada and USSR tests. Their estimated contribution amounts to a very small part of the temperate latitude bump shown by the data.‘ Other less certain arguments all add up to the same
picture: the bulk of the long-lived fallout in the temperate latitudes appears to have come from
the stratosphere. However, the main evidence —age determination by short-lived fission
products —suffers from possible defects due to fractionation and errors in radiochemistry.
New measurements are being taken of the stratospheric Sr® distribution and other, and perhaps more certain, short-lived fission products to further check whether delayed fallout is
uniform, or as proposed here, nonuniform over the globe. From existing evidence, it can be
argued that, even if the intermediate fallout were subtracted, there would be little doubt that a
marked peak of the stratospheric fallout in the temperate latitudes of the Northern Hemisphere
would still appear. The polar region may show smaller values due to the smaller amount of
precipitation or to the main injection into the troposphere entering the temperate rather than
polar regions.
_ A second prediction of the meteorology calls for a seasonal variation in the Sr” removal
from the stratosphere with a peak in the late winter or spring. Although Fig. 11 shows the
plot of 45-day fallout amounts for Milford Haven, England, in rain® (the solid line), similar
results are found for all of the U. S. stations®that sample rain water and air concentration.
The British were also able to sample and interpret air concentration of bomb radioactivity in
the lower stratosphere for a short time in 1954 and 1955, the results being shown by the heavy
dots. The left-hand ordinate is the concentration of Sr® per unit volume of rain water rather
than deposition per unit area. A plot of deposition per unit area shows just about the same
picture, indicating that the seasonai variation in deposition is not due to the fact that it rains
326
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