health and safety laboratory - Digital Collections

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SUMMARY
While the gummed film network fulfilled its original purpose of de
lineating fallout patterns, this report has been devoted to the extension of
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the p activity measurements to the estimation of Sr7 deposition and infinity
gamma dose. The computations have been based on a simple model, but yield
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Sr estimates that are generally within a factor of two from measured values.
It would be possible to improve the gummed film estimates by adopting
a more sophisticated model, but the added cost would not be justified. The
present results have required much greater effort than was expected and have
appeared more slowly than was hoped.
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The gummed film Sr estimates are lower in most cases than the
measured values at nearby sampling sites. The deviation is probably a com
bination of many effects:
1. The estimate of Sr yield may be low, particularly for fraction
ated, debris, where long range fallout is enriched in this nuclide.
2. The gummed film efficiency is variable and is probably lowest
during heavy rainfalls when a large fraction of the Sr^O is
deposited.
3. The gummed film efficiency continues to decrease in the absence
of large scale tests, for the percentage of long-lived Sr^° and
Cs 1^ increases and their retention is poor.
4. The present model is poor during periods of repeated high yield
tests, as there is no delay'included for arrival time from either
the troposphere or stratosphere. The debris is thus always con
sidered to be fresher than the actual fallout.
The results presented in this report have some value in the absence
of direct measurements. While it is not possible to evaluate all situations,
the data may be used for geographic interpolation between stations where Sry
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results are available. It is also possible to make reasonable estimates for
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