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{Reprinted from RADIOLOGY,Vol. 66, No. 4, Pages 535-94, April, 1956.]
Copyrighted 1956 by the Radiological Socicty of North America, Incorporated
Criteria for Evaluating Gamma Radiation Expesures
from Fallout Following Nuclear Detonations’
GORDON M. DUNNING?
IE RADIATION factor of greatest immediate concern to man in the fallout
incident to nuclear detonations is the external gammaradiation emitted from materia! after deposition on the ground.
This is the only factor that will be discussed here.
COMPARATIVE RADIATION DOSES AND
BIOLOGICAL EFFECTS
In evaluating the biological effects of
gainma radiation exposures from fallout,it
is natural to turn to the many experiments that have been performed in the
laboratory.
In making a comparison,
however, certain differences between the
- two sets of conditions necessitate consider-
ation.
First, in the laboratory, narrow-beam
exposures, unilateral or bilateral, have
been the rule, while radiation from a fall-
out field may represent a source in radial
geometry, t.e., the radiations reach a given
point from material which is spread over a
plane. A usual laboratory method is to
measure the air dose rate from a unilateral
or bilateral source at the proximal surface of the subject, and to report the dose
required to produce a given biological
effect. For larger animals this dose may
be significantly higher than one calculated
by integration of the air dose all around the
subject, which, in essence, is the situation
mals to die within thirty days) decreased
from 500 to 350 or £00 r when the method
of exposure was changed from unilateral to
bilateral (1).
Still further reductions
might be expected in changing to exposure
from a source in radial geometry.
Second, an experiment with Rhesus
monkeys (2) in which 250-kvp x-rays
were used gave an LD 50/30 value of 530 r.
A significant numberof the monkevsdied,
however, after the thirtieth day. If the
survival data at one hundred days (the
extent of the data reported) were utilized,
the figure (LD 50/100) might be ciose to
430r. While it is proper to report and use
LD 50/30 values for experimental purposes, such values are less relevant in the
present study, since we are concerned with
the general health and welfare of the pub-
lic. It is as serious for a man to die on the
one-hundredth day as on the thirtieth day.
That the factor of deaths after thirty
days may be extrapolated from one primate
to another is suggested by the Japanese
data (3). In the group sampled for Hiroshima, the number of reported deaths between the twentieth and twenty-ninth
day was 137; for Nagasaki the figure was
87.
After the twenty-ninth day 117
deaths were reported at Hiroshima and $7
at
Nagasaki.
(There
were,
of course,
when an air dose rate measurement is taken
many deaths in these sampled populations
before the twentieth day.) The difficult
task of accurately recording, isolating, and
posures may be produced by lower air
recognized, but an analysis of the extent
of radiation injury and the time of death
in a fallout field. Thus, biological effects
comparable to unilateral and bilateral exdoses as measured in a fallout feld.
This geometry factor has been shown to
have genuine significance for large antimals, such as swine, where the LD 50/30
values (the instantaneous dose of radiation that will cause one-half of the ani-
identifying the causes of these deaths is
would strongly indicate that radiation was
a major factor in a significant number of
the fatalities occurring after the thirtieth
day.
Tie final difference. between laboratory
exposures and doses from fallout requiring
1 Presented at the Forty-first Annual Meeting of the Radiological Society of North America, Chicago, IL,
Dee. Li-16, 1935.
"Health Physicist, Division of Biology and Medicine, U. S. Atomic Energy Commission, Washington, D. C,
585