-Se
in the sams latitude bend as the test locations, Tn Figure 3,
the 35-day cumulstive fallout from CASTLE BRAVO is show as a
series of isolines on the lower part of the figure. ‘The uppar
portion of the figure shows as the shaded area the regions of
the glore which, from moteorological considerations, were
expected to heve fallout in the first week or so. It is evident
that the band of highest fallout circles the earth in the tropics
of the northern hemisphere with only occasional north-south excursions,
The removal of particles in the intermediate range from the
atmosphere during dry weather is assisted by vertical eddies near
the earth's surface and by interception by obstacles. However, it
is likely that Rost importent fraction is removed by precipitation scavenging.
It has been found, for example, following most
of our Nevada test operations, that on days with rain, there is 10
times more radioactivity deposited on the ground than on days with
no rain.
The particles are probably large enough so that scavenging
by inertial effects are still important.
That is, the small radio-
active particle, because of their inertia cannot escape from the
path of the falling raindrop,
The budgeting of the fraction of radioactivity depositedin
the intermediate range as well as that in the delayed fallout
is quite uncertain.
Careful analysis of the world-wide fallout
network of the U. S, Atomic Insrgy Corsission after the IVY and
CASTLE test series suggests that between 1 and 5% of the fission
products which were formed fell out between about 1 and 30 cays
after each test operation.
The sams numbers for the interredlate
fallout from the Kevada tests amounts to perhaps 25%.
In the
latter case, the amount of the closz-in fallout is knam quite
exactly and since there is no delayed fallout, we can add tha local
and intermediate fallout together to obtain the total.
The result
shows that somsthing of the order of 50% of the radioactivity is
still unaccounted for.
Departreen? ¢f Enargy”
Histers*"s 24
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