784
GUSTAFSON, BRAR, AND MUNIAK
in a reentrant stainless-steel container for gamma-ray analysis. The
container fits over a 5-in.-diameter 4-in.-thick Nal crystal. Pulseheight analysis was done with a multichannel analyzer. The amounts of
the various gamma emitters present were determined by a computer
program and the use of appropriate standards according to a method
previously described.! The concentrations of the following fission
products have been determined: '“!ce—'4ce, !Ru—!Ru, sb, "Cs,
7 r—*Nb, and '“°Ba—'“°La when appropriate. In addition, the concen-
tration of “Mn in soil has been measured by this method. The concen-
tration of natural radioactivity is also obtained in the course of analy-
sis, and the dose rate due to the various radioactive species has been
calculated.”
Gamma-ray spectral analyses have been carried out on surfaceair samples collected on appropriate filters as well as on precipitation
samples. Monthly soil sampling during times of relatively high deposi-
tion of fission products coupled with air and precipitation measurements have led to the following empirical relation among airborne
radioactivity, precipitation, and deposition:
Deposition (mc/square mile) = rainfall (in.) x activity
concentration (pc/scm) x 28.3
(1)
These measurements were made during a time when nuclear testing was in progress and the concentration of debris in surface air was
quite variable from day to day. As a result the factor 28.3 was subject
to a rather large uncertainty, 28.3 + 14.1. Even so, when Eq, 1 is ap-
plied over a considerable time interval, the deposition calculated
agrees well with direct soil measurements. The monthly deposition of
'87Cg calculated according to Eq. 1 for the year 1963 is illustrated in
Fig. 1. The calculated ‘Cs deposition for the year was 78 mc/square
mile compared with 70 mc/square mile from soil core measurements.
Measurementsof '*"Cs in surface air at the site extend back to 1953, as
do measurements of local precipitation. The annual deposition has been
calculated for each year since 1953, and the values are shown in Fig. 2.
The accumulation of '*’Cs is plotted in Fig. 2, account being taken of the
radioactive decay of ICs according to a half-lifeof 30 years. The total
calculated accumulation of 310 mc/square mile as of August 1964 is in
agreement with the value of 330 mc/square mile measured in July 1964.
The annual deposition correlates with the time distribution and intensity
of nuclear testing that has occurred prior to the year of measurement.
As expected, the highest deposition occurred during 1963, and the second highest level occurred during 1959. The years 1960 and 1961, dur-
ing the test moratorium, showed low deposition values.
A considerable fraction of the total '"Cs uptake by plants is due to
freshly deposited debris, i.e.,"Cs deposited during the growing season