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164
RADIATION STANDARDS, INCLUDING FALLOUT
As brought out in past hearings, other qualifications and reservations, such
as the uncertainties of extrapolating data far beyond the point of observation,
lack of statistically established confidence limits, uncertainties in the use of
general assumptions where specific data are lacking (e.g., choice of shielding and
weathering factors), and the question of distribution of individual values about
the mean, should be recognized also.
With these reservations in mind, the data in table 2 may be used to estimate
the tetal population average 30-year genetic, 70-year bone and bone marrow
doses, and the I™ thyroid exposure from all weapon tests through 1961. Table
8 presents such estimates in relation to natural background exposure. These
data show that the presently estimated U.S. average T0-year bone and bone
marrow doses from all tests through 1961 (including the recent U.S.S.R. series)
are approximately the same as those estimated during the 1959 hearings for all
tests through 1958. This discrepancy is readily explained. The 1959 predictions
were based on the assumption that Sr” in the diet at that time was totally dependent on the integral surface deposition level. This assumption led to overprediction of the 70-year doses by approximately a factor of 2. This overprediction is
approximately equal to the predicted increase in dose as a result of the U.S.S.R.
1961 tests. The 30-year genetically significant dose from tests through 1958 was
estimated during the 1959 hearings as 50 mrad,
TABLE 3.—Maaimized significant tissue doses to U.S. population from all tests
through 1961 in relation to natural beckground exposure
Source of exposure
Natural background.-....-....-...--.----------------Weapon tests........- 2-22-22
Percent of background.._--______..-_...-.--.----.--+--
70-year
bone dose
(millirads)
70-year
bone marrow dose
(millirads)
30-year
gonad dose|
(millirads)
10, 000
1673
6.7
7, 000
2381
5.4
3, 000
4175
5.3
70-year
thyroid
ose
(millirads)
7,000
4649
9.3
1 Sum of whole-body external, whole-body internal, Sr® and Sr‘* exposures (from table 2),
2 Sum of external and internal whole-body exposures and 1/2.7XSr™ and Sri* doses.
osm of short-lived fission product dose, internal Cs!3? dose, and 30-year integrals of Cl‘ and external
s
oses.
4 Sum of I4!, external whole-body, and internal whole-body doses.
The present estimate from tests through 1961 is higher by a factor of about
3. As shown by the data in table 2, this large predicted increase is not due
entirely to the U.S.S.R. 1961 tests. Predictions made at the 1959 hearings assumed most of the genetic dose would come from internal and external Cs”
and failed to give much weight to the contribution from short-lived fission prodcuts. Their prediction, therefore, was a factor of approximately 2 too low.
That, plus the predicted U.S.S.R. 1961 contribution, accounts for the factor of
3 increase over the dose predicted in 1959.
One other observation to be made from the data in table $ is the rather high
average exposure to the thyroid. Although thyroid exposure was recognized
as a Significant potential hazard during the last hearings, it seems to be more
significant now as a result of the rapid fallout rate of fission products injected into
the lower polar stratosphere. It should be emphasized again, however, that
the dose estimates given in table 3 are not age-weighted average exposures for
the present U.S. population. They are maximum doses applicable to a hypothetical population that received the maximum possible dose from ail components of fallout exposure from all tests. It is impossible, for example, for a
child who would have had to be born in the spring of 1961 to receive the maximum 70-year Sr” dose to also receive short-lived fission product and I’exposure
fromtests prior to the 1958 moratorium.
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