Reprinted from Science, August 10, 1956, Vol. 124, No. 3215, pages 251-255.
same time and are mailed to the U.S.
Atomic Energy Commission Health and
Safety Laboratory in New York, where
their radioactivity is assayed.
Studies have continued of the collection characteristics of gummed film in
Radioactive Fallout
pots. Analyses of the data have been completed for an 84-week test period, indicating that the gummed film is 63 percent
efficient if we make the assumption that
the high-walled pots collect total fallout.
We consider that the pots provide the
through September 1955
Merril Eisenbud and John H. Harley
best practical estimate of total fallout,
and the data obtained from the use of
gummed films have therefore been corrected by a factor of 1.6,
Soon after the fallout-monitoring network of the U.S, Atomic Energy Commission was established in the United
States, it became apparentthat daily fall-
out observations could be madeby simple
procedures at great distances from a nuclear detonation, and the network was
expanded in October 1952 to include a
numberof locations beyond the continental United States. Additional stations
were again added in February 1954, and
since then the sampling program has been
conducted at 88 stations, including 26 in
the United States. These operate continu-
ously. Additional stations in the United
States are added when nuclear detona-
tions are being conducted in Nevada. The
overseasstations are listed in Table 1, the
continental stations in Table 2.
The data collected within continental
United States through August 1954 have
been reported in previous publications
(1, 2). In this report (3) are summarized the data obtained in the United
States and abroad through September
1955.
The principal objective of the monitoring program is to enable one to estimate the levels of human exposure produced by radioactive fallout at great
distances from nuclear detonations. Such
exposure may result from external irradi-
ation by radioactive dust deposited on the
surface of the earth or from internal irradiation by specific radionuclides that
enter the body by ingestion.
With respect to ingestion, strontium-90
is the nuclide selected for continuing at-
tention because, from the point of view of
the long-range behavior of the isotopes
The authors are on the staff of the Health and
Safety Laboratory, U.S. Atomic Energy Commiscsinn
New Vark
NY
involved in biological systems,it is poten-
tially the most hazardous. This is due in
partto its relatively long half-life (about
28 years) but, more particularly, because
of the chemicalsimilarity of strontium to
calcium and the possibility that strontium-90 can therefore be assimilated into
biological processes involving calcium
and ultimately be deposited in human
Methods of Estimation
Mixed fission product activity. When
the sample is received in the laboratory,
it is ashed at 550° to 600°C, and its beta
The data from the monitoring network
provide the following estimates for each
activity is counted. The potassium-40 activity of a known weight of potassium
carbonate is used as the basis for converting counts per minute to millicuries. This
activity is then calculated as of (i) the
cumulative surface deposits of mixed fission products and strontium-90. These
estimates are reported in millicuries per
date, usually the first day of the following calendar year. These extrapolations
depend on knowledge of the age of the
bone.
place wherea station is located. (i) The
square mile. (ii) The cumulative gamma
dose (in millirads) from external radiation.
Tt will be noted that the earlier publica-
tions did not include estimates of the
gamma dose. However, in recognition of
the increased interest in such estimates,
these data have been computed for the
full sampling period and will hereafter be
available on a continuing basis.
Method of Sampling
Adhesive-coated
films,
as
described
previously, are used for collecting samples. An adhesive coated acetate film is
supported horizontally on a frame about
3 feet above the ground. The coating re-
sampling day and (ii) an arbitrary future
sample, its decay being assumed to be
proportional to ¢-1-?. At any given time,
the sum of the extrapolated daily values
provides an estimate of the cumulative
radioactivity deposited at the sampling
station as of the arbitrary date.
Strontium-90. The strontium-90 content of the samples can be estimated from
Hunter and Ballou curvesof relative isotopic abundance (4), or they can be
measured directly by radiochemistry’
When the latter procedure is used, it is
desirable to collect the samples for a
period of at least 1! month to facilitate
the counting procedures, and a suitable
vessel such as a high-walled pot can be
exposed for this purpose.
The Hunter and Ballou curves were
used during this reporting period,
Gammadose. It is not possible to meas-
tains its adhesive properties when it is
wet, and the radioactive dust particles
that are entrapped in raindrops are collected, possibly by impaction against the
detonation. The normal gamma-radiation
duplicate sampling units, thus providing
origin is much larger in magnitude than
adhesive surface. Most stations maintain
some assurance against loss of samples.
ure directly the cumulative gamma dose
from fallout at a distance from a nuclear
background of cosmic and terrestrial
the gamma radiation from fallout, and
usually masks the latter completely. It is
Ses
comparison with those of high-walled