IV.
CONCLUSIONS
The important conclusions which can be drawn from the study are
summarized below:
A potential fall-out hazard is always associated with the detonation of a nuclear weapon, the amount of radioactivity being a
function of the fission yield.
This hazard may manifest itself on
either a local or a world-wide basis or both, depending upon burst conditions.
The proportions of available activity falling out locally and
world-wide are determined primarily by the location of the burst point
relative to the surface of the earth, and secondarily by the character
of the surface over which detonated, and by prevailing meteorological
conditions.
Following a ground surface detonation, most of the gross radio-
active materials are incorporated into earth particles, with the largest
percentage, which falls out soon after the detonation, being on particles of 10 to 1000 microns diameter.
The local fall-out after CASTLE
Bravo shot is estimated to involve roughly 50% of the total activity
available.
Contour scaling laws in current use in the megaton range are
pased on weapons which have a fission to fusion ratio
Anv
deviation from this ratio will vary the amount of radioactivity deposited at any given distance from ground zero.
As a first approxima-
tion it may be assumed that for a given total yield, the activity represented by a given contour is directly proportional to the fission
yield.
Raising the total yield of the weapon without raising the
fission yield will spread the given amount of radioactivity over a
larger local area.
Potentially lethal fall-out intensities resulting from landsurface bursts of nuclear weapons with fission yields in the megaton
range are likely in each case to involve areas of thousands of square
miles.
Such lethal areas can be drastically reduced in size if the
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