I.
INTRODUCTION
Page
For the past several years the Health and Safety
Laboratory has been conducting a detailed investigation of
the properties of the external radiation environment.
Previous reports have described the development of field
gamma spectrometric technigues utilizing high pressure
ionization chambers and a 5" x 3" NaI(Tl} detector."
These technigues allow reasonably precise and accurate
estimates to be made of total open field gamma dose rates
from each of the important individual components of the
natural and fallout gamma radiation field.
The results of
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a number of field studies utilizing these technigues have
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also been reported. *
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The development of these techniques has made possible
more detailed investigations of various aspects of the
external radiation environment such as the variation of
natural dose rates with time, geographical differences in
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fallout distribution, cosmic ray ionization variation with
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altitude, and B-ray ionization effects.
In attempting to
investigate these problems we have found it necessary to
improve our instrumentation by acquiring new more sensitive
NaI(Tl)
ivity
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detectors with much better resolution
and stability
than the 5" x 3" detector which our initial system utilized.
Section II of this report describes these new detectors and
discusses the laboratory calibration and calculations undertaken to allow total and component dose rates to be inferred
from their response.
This improved instrumentation was used to study the
external radiation field in more detail under a wide range
of geographical conditions and radiation levels during an
extended survey trip undertaken in August and September of
1965.
Section III of this report describes the many
different investigations carried out during the course of
this trip.
Using our spectrometric techniques in conjunction
with high pressure ionization chamber readings over both
land
and on lakes
at various
altitudes,
we were
able to
infer the variation of cosmic ray ionization intensity with
altitude.
Our spectrometric techniques were extended to
the determination of 13’cs concentrations in soil at a
number of sites throughout the United States.
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These data