times and reach the ground some distance downwind.
These more distant
particles tend to have more cesium (daughter of gaseous xenon) and
stroatium (daughter of gaseous krypton) relative to other fission product
activities than do the heavier, and thus nearby, particles.
Thus,
the rather few surface explosions at Iniwetok Atoll tended through
fractionation to result in the amounts of cesium-137 and strontium-90
deposited on the test island and nearby islands being less relative to
other fission products than the amounts produced by fission in the
nuclear explosion.
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An example of this fractionation is provided by analyses of the
particles in the cloud from the La Crosse test (Nathans, 1970),
La
Crosse was a coral surface burst of about 40 kilotons on Runit Island.
The camnle nf the radioactive cloud was collected at 6500 meters at
2.6 hours after the event.
The specific activity (the radioactive
with a smaller 9-micron diameter particle.
(Little variation was
found in specific activities between the smaller particle sizes ranging
between 0.5 and 13 microns.)
Radionuclide
Specific Activity for 9 microns
Specific Activity for 50 microns
strontium-90
296
promethium-147
229
uranium
0.47
5
“
SOMES ed Tk TI, A aWer’
factors when the largest particle of 50-microns diameter is compared
newnanan: *
was found to increase with decreasing particle size by the following
so eee ire ane rae a
disentegrations per unit time and per unit weight of the particle)