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SASS
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RADIATION STANDARDS, INCLUDING FALLOUT
Representative Price. Without objection, your statement will be
carried in full, and the document you mentioned will be carried in
the record.
Dr. Lancuam. Thank you.
(The documents referred to follow:)
GamMa Ray Dose From SnHort-Livep Fission Propucts FroM NUCLEAR-WEAPON
TrstTs
Philip F. Gustafson, Division of Biological and Medical Research, Argonne National Laboratory, Argonne, Tl.
The y-ray dose from short-lived fission products deposited on the ground may
constitute the major source of whole-body radiation during the testing of nuclear weapons in the atmosphere and for some months thereafter. The magnitude of this dose relative to that from ground-deposited Cs™ depends critically
upon the time that it takes nuclear debris to travel from the site of detonation
to the point of deposition. The transport ‘time in turn is dependent upon the
size of the detonation, the altitude and latitude at whi.’ it occurs, and the time
of year of its injection into the atmosphere.
Nuclear debris from a small (kiloton range) surface burst is confined within
the troposphere and hence is completely deposited within a few months. Asa
result the amount of short-lived radioactivity relative to that from Cs™ is
large, although the absolute magnitude of the concentration is small. In the
ease of a high-altitude burst (30 kilometers or higher), regardless of size, many
months and even years may elapse before an appreciable fraction of the debris
reaches the ground. The decay of much of the short-lived component before
deposition leads to a lower dose relative to Cs”. There is also a latitude effect,
in that debris injected into the low polar stratosphere (a portion also being
present initially in the adjacent troposphere) will be deposited somewhat more
rapidly than that from an equivalent injection into the low equatorial
stratosphere.
The rate of removal of nuclear debris from the stratosphere is not constant,
but undergoes seasonal variations, being greatest during the spring months
in the hemisphere in question and least during the autumn and winter. The
corresponding variation in the concentration of Cs, for example, in surface air
is illustrated in figure 1. The repetitive cycle of maximums and minimumsis
of meteorological origin as shown by its occurrence during 1959 to 1961 in the
absence of nuclear testing. This phenomenon is believed to result from the
subsidence of the airmass over the winter pole with a subsequent influx of
stratospheric debris into the lower atmosphere during the spring. The strong
influence of the polar stratosphere explains in large part the more rapid removal
of debris injected in polar regions. The variation in removal rate from one
month to the next does not preclude a reasonably constant annual removal rate.
A measure of the annual removal rate or mean stratospheric residence time
may be obtained by comparing successive maximums or minimums as shown
in figure 1.
Three nuclear test situations will be considered regarding the gamma ray
dose due to short-lived fission products: (1) Injection into the low polar stratosphere, (2) injection into the low equatorial stratosphere, (3) high-altitude
detonation or injection. Small detonations. whose debris is contained within
the troposphere, will not be considered because of the relatively small amount
of radioactivity produced therein.
The following radionuclides have been considered in computing the y-dose
from fission products on the ground: Zr®-Nb™, Ru'®. Ru’, Ce, Oe!pr,
Ba-La’®, and Cs. I has been omitted because of its short half-life. Sb**
becomes of some relative importance 2 years after a test; however, the accuracy of measurement of this nuclide in soil has not been sufficient to warrant
its consideration at this time. The concentration of the various nuclides in
soil has been determined by means of gamma ray spectrometry of soil cores.
Monthly increments in deposition have been determined in part by direct
analysis of soil and in part by analyses of precipitation and air samples.
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