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THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
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SHORT TERM RIOLOGICAL FATE, PERSISTENCE OF RADIOACTIVE FALL-OUT
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TIME OF SAMPLING (DAYS AFTER SHOT)
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Figure 5.—The occurrence of radioiodine in the thyraid
of native animals serially sampled from a fallout coulaminated area 12 miles from Ground Zera and on the
approximate midline of fallout [1].
AI
Frovne 3,—-A dried peli taken from a kangaroo rat exposed to fallout 16 miles from Ground Zero and the resulting
autoradiogram showing the occurrence of radioactive fallaut particles (3],
Figure 4 summarizes the persistence offission
products in various tissues serially sampled from
a natural population of kangaroo rate over a
period of 90 days following a single fallout contamination in the spring of 1953. The decrease
in tissue burdendoes not deviate markedly from
the theoretical decay of mixed fission products
besed upon the t-4.? decay constant. This suggeats thet the tissue burdens are made up of
mixed fission products in equilibrium with the
concentrationof fission products in the environment. During this time period there appears to
be little evidence of biological concentration of
fission products in terms of gross beta gamma
activity. Figure 5, however, shows the gradual
buildup of radioiodine in the thyroid of kan-
garoo rats and jack rabbits serially sampled
from « fallout arca located 12 miles from
Ground Zero during the spring of 1955. Sampling was discontinued 15 days after fallout
with the concentration of radioiodine still rising.
It can be anticipated, however, that the accumulationof iodine was nearing its peak. This
buildup of thyroid activity corresponds to similar phenomena described at Hanford Works and
is consideredto reflect the time necessaryfor the
iodine in the thyroid and in the food supply to
reach equilibrium. The problem is further complexed by the identification of Ias the primary
contributor to thyroid activity during the first
day or two following fallout following which
time 1" becomes dominant,
Figure 6 shows the influence of the location
of the sampling site within the fallout pattern
to the biological accumulation of fission products. In this case the accumulation of fission
products is plotted against the distance of the
sampling site from Ground Zero along the
midline of fallout. As might be expected the
tissue burdens generally appear to drop off
with distance but not as sharply as does the
total fallout.
Note the striking deviation of
the femur and kidney data from the other
tissues.
Figure 7 presents similar data from
two separate events showing the increase in
radioactive content of the thyroid as a function
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TIME Of FIELD SAMPLING (DAYS AN TER DETONATION)
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Fravre 4.—-The occurrence of fission products in tissues
sampled from a natural population of kangaroo rata
living 19 milea from Ground Zero in a fallout contaminated enviranmeni expressed as a function of time
after fallout {3}.
of distance from the sampling site with a peak
concentration at 60 miles from Ground Zero.
Note that this distance is the same for botu
fallout patterns even though the conditions of
detonation were very different. These data
just presented are all from samples collected
within 24 to 48 hours following fallout.
Figure 8 shows the interaction of time, and
the position of the sampling site on the bio-
logical fate of fallout.
Following the 1955
test series, two residual fallout patterns were
defined and samples taken along the midline of
contamination.
The results from one pattern
are shown in Figure 8 since these data are more
complete and representative of both residual
fallout patterns. The environmental contamination, a measure of gross residual fallout.
contamination, decreased sharply with distance.
The gross beta gamma.activity in jack rabbit
bones sampled along the midline of residual
fallout inereased out to 130 miles and then
decreasedslightly and leveled off. The radiation levels above normal that occurred in the
bone ash was accounted for by the presence of
radiostrontium. The peaking of activity at
130 miles appeared more specifically to be
attributable to the relatively heavy concentra-
tion of Sr®*.
This was not the first time that this phenome-
non had been observed.
In May 1954, one year
following the 1953 Test Series, another residual
fallout pattern was studied to a distance of 130
miles from Ground Zero, with the results that
are summarized in Figure 9. Once again soil
contamination was shown to fall off sharply
while the burden of radiostrontium in jack
rabbit bones increased to a maximum at 130
miles fram Ground Zero.
Remember that with respect to the iodine
data the maximum value occurred at 60 miles.
The maximum in the strontium data occurs at
130 miles. Another parameter can be assumed
as the time necessary for the parent fission
products to decay into the daughter products