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RADIATION STANDARDS, INCLUDING FALLOUT
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Todine 131
Since the 1957 fallout hearings, [™ has become increasingly recognized as a
rather significant component of population exposure from fallout. Lewis (20),
in the 1959 hearings, called attention to the potential hazard to children of the
TEcomponent of fallout exposure.
Although I'” has a radiological half-life of
only 8 days, it finds its way readily into milk and from milk into the human
body, where it concentrates almost exclusively in the thyroid gland, Because of
the short half-life, radiation exposure occurs only during tests and for short
periods thereafter, and the concentration in the thyroid is critically dependent
on the time it takes to travel from point of detonation to site of deposition.
Rapid localization in the small thyroid gland (~2 grams in the infant to ~18
grams in the adult), however, can result in rather high radiation doses. The
fact that the infant with its very small thyroid consumes largely a milk diet
makes exposure of the infant population a potential problem. Since the 1957
hearings, considerable data have been collected on the concentration of I” in
the thyroids of the population in relation to frequency and location of nuclear
weapon detonations. The milk surveillance program of the Public Health
Service has contributed materially to present knowledge of this component of
population exposure, Their evaluation of the problem (8) is presented as a
part of the programof the present hearings.
POPULATION EXPOSURE FROM FALLOUT
Estimates of U.S. population 70-year exposures contributed by the various components of fallout from all tests prior to the moratorium (November 1958) and
from the U.S.8.R. 1961 series are shown in table 2. These values were chosen
from various references or derived from various concepts which, to the authors,
Seemed reasonable. No strong argument can be made that these estimates are
more accurate than similar ones made by others. The following qualifying
Statements are necessary before trying to draw any general conclusions from the
estimates: (a) The estimates are averages for that age group receiving the maximum 70-year integral exposure (usually the 0- to 2-year age group); (b) the
averages apply generally to the U.S. population in the 30- to 60-inch rainfall
region and perhaps generally to north temperate population belt; (c) estimates
for the 1961 U.S.S.R. tests are based on the very uncertain assumptions that
25 megatons of fission were injected into the stratosphere and that it was
deposited in exactly the same manneras their 1958 tests. This latter assumption
is not being borne out by recent experimental observations (6). For this reason,
estimates of the U.S.8.R. 1961 contribution to population exposure, especially
with regard to external dose from short-lived fission products, may be too high.
TABLE 2.—Mazimized contribution of the carious components of fallout to the
U.S. average 70-year population dose*
Component
Due to all
tests prior to|
moratorium
(mrad)
External (whole body):
Short-lived fission products...__.......____. donee eee eee
Cesium 1387..... -_-..... ee ee
Total
(mrad)
i 57
42
vb
41
a1
76
18
17
19
1 46
Internal (whole body):
Cesium 137.____.... __- ecae cael) lee ee eee ee leeeee ae
Carbon 14_______ (wel eee ones eee ne
Skeletal deposition (structural bone):
rontium
9.202 0.
4
Iodine 131 (thyroid)... Cece eee ee ee ee
* 200-400
Strontium 8000000 coors Soe
Due to
U.S.S.R.
1961 tests
(mrad)
28
128
4
38
6 140
74
m4
340-540
1 From data of syustatson(6), using building shielding factor of 0.5 and body shielding
factor of 0.7.
* From Anderson et al. 7
i Estimated from factors proposed by Prediction Panel, these hearings.
uthors’ estimates, based on data of Kulp and Schulert (4) and fallout models of Machta (21).
; Values of Lewis (20)
Public Heaith Service report (8), these hearings,
*GENERAL NOTE.— In all calculations, the data of Dunning (3) were used for fission
and fusion yields.
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