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RADIATION STANDARDS, INCLUDING FALLOUT
RapIaTION Exposure TO PEOPLE From NucLEAR WE4PON TEsts THROUGH 1961
By W. H. Langham and E. C. Anderson, Los Alamos Scientific Laboratory,
University of California, Los Alamos, N. Mex.
INTRODUCTION
Past subcommittee hearings (1957, 1959) on the subject of radioactive fallout
from nuclear weapon testing have produced voluminous reports (1, 2) covering
all aspects of fallout phenomena, exposure of the population, and possible
biological effects. Little can be added at the present time to the basic concepts
set forth in the previous hearings. Collection of additional data during the
test moratorium from November 1958 to September 1961, however, has afforded
basis for more quantitative definition of some of the physical and biological
parameters. Better quantitative definition of the following parameters has
resulted in refinement and improved accuracy of average population exposure
estimates: (a) Fallout rate and integral surface deposition level as a function
of point of stratospheric injection; (b) dependence of dietary level on differential and integral fallout; and (c) dietary and metabolic factors. More refined
estimates of population exposure from various components of fallout have been
made by a number of investigators and agencies, notably Dunning (3), Kulp
and Schulert (4), Gustafson (5, 6), Anderson et al. (7), Public Health Service
(8), Defense Atomic Support Agency (9, 10), the Federal Radiation Council
(11), the United Nations (12), and the Prediction Panel of the present hearings
(18).
Since the 1959 hearings, one additional factor has influenced the estimation
of exposure of people from fallout: ie, the resumption of tests by both the
U.S.S.R. and the United States. The purpose of this rather brief presentation
is not to present details of the refined dose calculations but rather to summarize the present estimates of population exposure level from long-range
fallout, taking into consideration the 1961 U.S.S.R. test series and the additional quantitative data collected since the previous hearings.
PARPRRRCL
COMPONENTS OF FALLOUT EXPOSURE
Radiation exposure from long-range fallout (independent of local fallout
which is of primary concern in event of war) is composed of several components,
each of which will be discussed briefly prior to summarizing the population
dose contributed by each. Depending on the component, exposure may be either
internal (i.e, from radionuclides taken into the body through food chains)
or external (from deposition of gamma-emitting isotopes in the environment),
or both. As pointed out in previous hearings, the relative contribution of
each component to the integral dose is dependent on a variety of factors, including radiological half-life of particular radioisotopes, biological uptake and
turnover rates, fallout rate of each injection, and in some cases even on the
age of the individual exposed. These and other factors produce such degrees
of complication that any detailed review of their significance in the dose estimations is impractical for the purpose of these hearings.
Strontium 89 and strontium 906
Because of the chemical similarity of strontium and calcium, isotopes of the
former element are taken into the body and deposited in the skeleton. Since
both Sr“ and Sr® emit beta particles only, they produce no genetic hazard,
and their somatic hazard is confined entirely to the bone and bone marrow.
Animal experiments have proved unequivocally that enough Sr® and Sr” deposited in
the skeleton will produce bone cancer and other skeletal pathology.
The amounts of these isotopes required to produce bone disease in man are
not detinitely known. Because of the short half-life of Sr(51 days), it contributes to the bone dose only during the first year of fallout and does not
accumulate in the ecological cycle.
Strontium 90, with its 28-year radiological
half-life and its 30-year biological turnover time, can integrate in the soil and
in the bone and contribute significantly to skeletal radiation throughout one’s
entire life.
For this reason, it is a major component of fallout exposure.
Be-
cause the rate of growth of the skeleton is dependent on age (up to 20 years),
the present concentration of Sr” in the bones of the popwiation is likewise
dependent on age. The quantitative explanation of the age-dependence of Sr
concentration was given by Langham and Anderson
(14)
and has since been
refined. and proved experimentally by Kulp et al. (4, 15, 16, 17, 18).
The age
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