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ing aloft for long periods.
In the application of this method, coincident samples of gas and
particles are taken by an isokinetic collector during the first few hours
of existence of the clouds,
The nuclear aerosol is sucked through a filter
to remove the suspended material and the particle-free gas is then pumped
into a storage bottle.
The number of fissions in the two samples is deter-
mined by analyzing the gas for 2, 8-hour Kr°8 and the solid for a representative nuclide such as Mo?9,
The ratio of sample fissions calculated from a bound nuclide to
those from an unattached rare gas nuclide will give the fraction of the. .
reference substance which is in the cloud at the time of sampling.
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very early time, before any appreciable fallout has taken place, this
ratio should be one, but later it would be expected to decrease as the falling particles remove the bound fission products.
Hence the fraction of the
material in world-wide fallout may be determined if the time is knownat
which particles having a falling velocity of 3 inches per second leave the
sampling region.
1.2.5 Prior Estimates of Local Fallout.
Determinations of local
fallout have been made at virtually all the nuclear weapons tests conducted
by the United States.
Estimates of the fraction of the radioactivity deposi-
ted locally have been made for Operations JANGLE (References 16, 23, 25,
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