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100 picocuries per em” would contain about 4 x 10° particles per
square meter.
If all of these particles were on the soil surface
and therefore available for resuspension, there would be initially
only 4 particles per cubic meter of air for a resuspension factor (RF)
value of 107°,
This air concentration would decrease exponentially
with a half-life of around 30-40 days as the particles remaining on
the soil surface become less available for resuspension.
The Concentration Guide for continuous inhalation of 239py is
1 pCi/m (averaged over one year for the individual in the population).
Thus, initial ground concentrations of 100 picocuries per gram (assuming
a gram per em® of surface) may be taken to correspond to a deposition
of 10° pCi per square meter.
For a RF value of 1076, the initial air
concentration would be 1 pCi per cubic meter.
This value would decrease
as a function of time because the plutonium becomes less available for
resuspension.
Based on the highest reported plutonium level at Bikini Island,
190 pCci/g, and assuming this plutonium to be recently deposited and
on the surface, a conservative estimate is that the total lifetime
dose to the lung would not exceed 70 millirads.
Other Data.
A brief verbal report was obtained April 6 from Dr. Robert
Conard of Brookhaven National Laboratory who has just returned from
conducting another in the series of medical studies for the natives
Mo
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