is reduced) the soil in the stem becomes tore active, thus producing
heavy contamination immediately downwind.
The total percentage fall-
out increases with yield (when height is constant), but the percentage
fall-out from the mushroom decreases with increasing yield.
To a per=-;
son who has not analyzed the total fall-out picture and who only chooses
to utilize ground readings, the fall-out problem must appear even more
complex than it really is.
As a matter of fact, recently a set of
empirical relations has been develeped on fall-out from tower shots
utilizing only the ground readings from J/'K Test Operation.
The air
readings were not utilized out of impatience or lack of knowledge on
how to use them.
The T/S Test Cperation data were not used because
they were more difficult to reduce, since most of the fall-out during
T/S Test Cperations fortunately occurred North and Northeast of the
Test Site where there are very few good roads and very little popula-
tion.
Sure enough a set of relations were developed which indicated
intensity of fall-out to be independent of yield.
Here is a good
example of the need to evaluate all of the data before empirical relations are developed.
B.
Construction of the Forecast Fal.-out
l.
Particle
Size
Assume that the particle size distribution within a nominal
bomb expucded at 300 ft is 100 microns if the maximum cloud height does
not reach beyond 35,CCO ft msl.
The maximum cloud height is a function
of the yield, the height of the tropopause, the lapse rate of the atmosphere and the speed of the horizontal winds.
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A nominal bomb cloud will
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