is indicative of greater soil water content during the 1965
measurement period compared to that of 1962 and 1963.
These
areas experienced greatly increased rainfall during the
previous year or so while the Northeast experienced drought
conditions.
During the 1962 and 1963 surveys extremely dry
and dusty conditions were prevalent over much of this area.
The Denver area,
in particular,
experienced widespread
flooding during the spring of 1965.
This increased moisture
is reflected in the Denver data (Table IV).
The effect of
moisture in the soil on dose rates and spectrometric dose
rate measurements is being studied in some detail. (See
Section IV.)
While the major fallout contributors to the gamma dose
rate in 1962 and 1963 were 9°9zr -— 95Nb and 106pn, the major
contributors during 1965 were 137cs, 196Rh and 54mn with
traces of 125sb and 144ce - 144pr detectable at almost all
soil locations.
Studies of Cosmic Ray
Ionization
In order to study cosmic ray ionization as a function of
altitude spectra were obtained over a number of large lakes
at various altitudes up to 10,000 feet.
These results are
given in Table V.
The measurements at Red Mountain and at
an open pit asbestos mine near Copperopolis, California
shown in Table V are considered as cosmic ray measurements
and treated with the lake measurements since the serpentine
rock at both these locations exhibited very little gamma activit
The 4" x 4" detector was placed in its stand as used in the
field facing downward® at one end of a small aluminum or
fiberglass boat.
In all cases measurements were made more
than 1/2 mile
from shore to minimize
interference
from gamma
emitters in the soil.
All of the spectra indicated the presence of some gamma
activity.
Two representative cosmic ray ionization spectra
are shown in Figure 2.
The only significant gamma contributors
were radon daughters in the air.
As shown in Table V our
estimates of the gamma dose rate from the spectra range
between 0.1 ur/hr and 0.5 ur/fhr.
Using these gamma dose
rates we have estimated for each lake spectrum the total
"energy" in the band 0.15 MeV to 3.4 MeV due to cosmic ray
secondaries.
The cosmic ray response for each of the three
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