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Measurements of Low Level Radiation
Measurements were made at three locations where gamma
fandfor cosmic ray dose rates were unusually low in order to
study our instrument response as well as for general interest.
The results of these measurements are also given in Table V.
The first location was an abandoned magnesite mine on
The serpentine
Red Mountain in Santa Clara County, Calif.
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wall material exhibited almost no detectable gamma activity.
Since the overhead cover was 430 feet of rock the dose rate
‘from w mesons was reduced to a negligible amount.
A two
outside
from
activity
detectable
hour spectrum showed the only
of the detector itself to be from radon daughters in the air,
resulting in a dose rate of less than 0.1 ur/hr.
No inherent
radioactivity sufficient to affect any of our field measurements waS apparent in any of our instruments.
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Directly outside the mine the serpentine material was
‘also very low in natural gamma activity with the only
‘Significant gamma activity coming from deposited fission
products.
Thus this set of measurements was a useful
jaddition to our lake data for our cosmic ray ionization
study.
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The second location was at the open pit asbestos mine
near Copperopolis, Calif., where measurements had been
taken previously.
The site where measurements were made
during the trip was only recently excavated and thus was
ave
completely clear of fission product activity.
not
otassium
the
affecting
activity of the
ossible
tive due
itself was
an excellent near sea
level measurement
in our cosmic ray ionizationstudy.
* 7
for use
:
The third location was in a deep salt mine near Houston,
aoe
The major sources of activity in this mine were from
pK in the salt and radon daughters in the air.
The total
dose rate measured was about 0.2 ur/hr.
eer
te orn
The natural
almost negligible
and again the only significant terrestrial gamma activity
was from radon daughters in the air.
(See Figure 2)
The
total terrestrial gamma activity was estimated from the
Spectrum to be less than 0.2 ur/hr and thus these data
provided
iderably,
ration
serpentine rock