The basic fallout datum obtained at the Health and Safety Laboratory is the beta activity of mixed fission products collected on gummed
film in units of d/m/sq.ft./2h hrs.
In comparing various samples each sample
is assumed to come from a specific burst and the activity is extrapolated to
a fixed date.
In addition, an efficiency factor of 1.6 should be included
to correct for loss by the gummed film,
This factor is based on experi-
mental data obtained during an 84 week period at New York.
It is not possible to make a direct measurement of the gamma dose
resulting from normal fallout away from the test site since the activity is
very low; however, it is desirable to have an estimate of the cumulative
gamma dose which might arise from continued fallout in a given area.
The
following calculations are designed to allow an estimate of gamma dose based
on measurement of the beta activity in fallout.
There are certain assuzptions made which are justified in the text
where required.
These are
1)
The activity is considered to come from a smooth infinite
2)
The activity is uniformly distributed over this plane at any
3)
The majority of the gamma dose is received from direct radia-
l)
The dose can be based on an average gamma energy rather than
a summation of individual values.
5)
The beta activity decays according to the T7L:2 rule.
6)
plane Source.
given location.
tion and no scatter contribution is included.
The isotopic abundance follows the values given by Hunter and
Ballou for slow fission.
The first assumption gives = hich estimate for dose since the
activity is not entirely at the surfe:2
‘vhis high estimate is compensated
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