4
tium-90/total-fission-product-activity ra-
at' least ‘part of the time. These data art
caused by the attribution of activity to
that the gummed-film system, together
with the above-mentioned method of
computation, yields estimates of strontium-90 deposition which tend to be
higher than the estimates derived by
radiochemical analyses of pot samples.
The mean ratio of strontium-90 estimated from gummed-film to pot analyses
#is 1.45, with a maximumratio of 1.66
at Salt Lake City and a minimum of
0.90 in New York City.
The calculation of external gamma
dose is less sensitive to variations in the
tio is calculated,
5) Each day’s measured beta activity
is converted to strontium-90 activity by
use of this factor.
This method of calculation would give
high strontium values for locations near
test sites on days of high fallout. This is
the total accumulated pool of fission
products rather than tothe immediate
burst which caused the fallout. This can
be corrected by treating these few cases
individually. _
The major approximations of 1s
technique are as follows:
1} Tropospheric and stratospheric debris: enter a pool which contributes to
shown in Table 2, in which it is shown
source of fallout. In addition, it appears
i
Pe
HEH E
Fi
ERE
bi
BH BE
rm
that the important gamma dose from
fission products is ffom internal cesiumthe fallout at each location.
137 rather than from the external gamma
2) The mixed fission products from_ radiation from distributed fission prodeach detonation decay according|to°the- ucts after suitable allowance for shield- _
i} law,
*
‘ing: and ‘weathering.
3) The relative tropospheric and
stratospheric depletion rates 2are not cons;
Conclusions.
sidered at this time:~
a
The only practical means‘of evaluating the new calculation technique is
The-range of -values. for strontium-90
by comparison with radiochemical analydeposition through June 1957 in the
ses of open samplers. During the period
United Statesis 11 to 54 millicuries.per
' from May 1956 to June 1957, several
square mile, which is somewhat higher
locations had parallel sampling units for
than otherlarge land areas of the world,
Excladirig the United! States, deposition.
in the Northern Hemisphere averiges' 6
millicuries per square mile, about twice
the average for the somewhat fewerval-
ues reported in1 the Southern’ Hemi-—
Sphere, |
.
The calculated external gamma doses given in Table 1 are estimates of the_
infinity doses and have not been cor- -
rected for shielding and weathering. Our,
best estimate of the actual external dose
to the population is approximately 10
percent of the tabulated values. The
dose may actually be lower, but a factor.
of 10 is a conservative estimate of the
effect of shielding and weathering.
References and Notes
1. W. F. Libby, Proc, Natl. Acad. Sci. U.S. 42;
365 (1956);
, ibid. 42, 945 (1956); Joing
Committee on Atomic Energy Hearings, “The
Nature of Radioactive Faliont and Its Effects
: on Man" {Goverament PrintingOffice, Wash:
ington, D.C.,.1957); M. Eisenbud and J.H.
Harley, Science 117, 141° (1953);
, ibid,
121, 677 (1955);
, ibid, 124, 251 (1956).
2. We wish to acknowledge the continued coop-‘eration of the U.S. Weather Bureau in the -cole=
lection of
id -film
The comp
+ les.
3.
tions and data handling were.performed by Dr.
A. E, Brandt and Dr. George D, Dicht of-the ©
Biometrics Branch of the Health and Safety
Laboratory.
H. F. Hunter and N. E. Ballou,| Nucleonics 9,
No. 11, C-2 (1951), *-- © +:5--
4, N, A. Hallden and J. H. Harley, AEC TISE
Rept, No. NYO-4859 (1957).