ae
produced (about 20% of tower shot debris) is believed to have been deposited, generally in
narrow plumes. Maximum downwind “hot spot” dose rate from tower shots has been in
the order of 1 r/hr at 3 hours, corresponding roughly to the deposition per square mile of 0.01 KT
of fission debris.
Data on close-in fallout from multi-megaton detonations are available with reasonable reability only for the coral atoll surface shot of March 1, 1954. This was estimated to be very
roughly 50% in a plume extending several hundred miles east. Exclusive of the downwind
islands in Bikini atoll itself, the nearest island in the fallout path (at a distance of 100 miles)
had a dose rate of roughly 250 r/hr at 6 hours after detonation, corresponding approximately to
2 KT of fission debris per square mile.
2. World-wide gummed paper collections:
Systematic gummed paper collections at a large number of points throughout the United
States have been carried out for all five American test series since October, 1951.7"! Foreign
collections have been made for all three tests since November, 1953.9 Data from the Pacific
tests of 1954 are as yet available in only preliminary form.
2
2
The distribution in the United States of debris from hoth the Nevada and Pacific tests has
been observed at approximately 100 weather stations. Since fallout in each series has been
dominated by 2 or 3 shots, the statistical variation in trajectory and therefore the area of fallout
has given greater geographical nonuniformities than would be the case for a large number of
shots. The February 1954 contamination in the United States was dominated by the test
series of the spring, 1953, with somewhat less contribution from spring, 1952, much less from
the Pacific tests of 1952, and only a small component from ali other tests. Cumulative activity
in the United States in February 1954, was about 1,000 dpm/ft ? over most of the country, assum-
ing 100% gummed papercollection efficiency. The West Coast was lower by a factor of perhaps
10, Nevada and states east to Colorado were higher by a factor of about 2 or 3, and Florida was
lower by a rough factor of 2 or 3. There were apparently some isolated small areas of activity
greater by as much as a factor of 5 or 10 than their surroundings. Nonuniformities were presumably greatest near the test site, but high local rainouts have been observed as far east as
Albany, N.Y.
The distribution in foreign countries of debris from Nevada tests has been observed essentially
in only one series, spring, 1953, at 12 stations outside North America. Interpolating through
weather data between the widely separated stations, the following picture of world-wide fallout
per unit area relative to that in the eastern U. S. can be inferred:
Southern hemisphere... 0... ee
North Atlantic, north temperate zone in Europe and Asia...
Arctic 06 eee
North Pacific........... en
North tropics (Atlantic)
=. ee.
North tropics (rest of world)......0 0.0... oo ee
<1%
15-40%
<15%
5%
5-15 %
2-10%
The world-wide distribution of debris from the Pacific tests of November 1952, is a complicated pattern. North America and South America to 20°S. latitude showed fallout varying unsystematically over a 10-fold range, with an average of about 700 dpm/ft ? as of 1 January, 1953.
Western Europe, Africa, and Asia as far east as India, averaged about 150 dpm/ft?, again with
considerable spread. The Asian Pacific seaboard and Pacific Islands showed wide variations
ranging from a high of 230,000 dpm/ft ? on Iwo Jima to levels of a few thousand dpm/ft*. These
data are difficult to interpret for the following reasons: (1) Origin of debris, whether from
large yield surface shot or smaller air burst, is ambiguous. (2) Amount of close-in fallout is
Footnote references on pp. 42-43.
8
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