radiation field.
Therefore, its
stakes at a height of 1 m above the
response is often used as a
ground.
reference to which other measure~
chosen to obtain exposures over the
ments may be compared.
full range of gamma exposure rates
The chamber
The locations were carefully
walls are sufficiently thick to
observed by the portable instrument
render the detector insensitive
survey.
to the beta radiation present in
period, the dosimeters were retrieved
fallout fields.
and handcarried (by air) in a lead
The instrument is,
however, sensitive to cosmic
After the 3-month exposure
container to Livermore for readout.
radiation.
We studied calibration and signal
“""" Further gamma exposure rate
fading by exposing separate sets of
comparisons were made by means of
TLD's to a 1376, point source before
LiF and CaF,: Dy thermoluminescent
and after the exposure period.
dosimeters (TLD's) placed at 80
special low-scatter calibration
locations.
fixture was constructed for field use
The LiF chip displays
A
an' essentially flat energy response
which aided in obtaining uniform,
and excellent thermal stability.
reproducible exposures.
The response of LiF is within
of the 1370, calibration source was
approximately 1Z of being air
determined by
equivalent for a typical environmental radiation field.
@
The CaFo:
Dy TLD's have an enhanced energy
The intensity
Using a NBS calibrated Radocon*
chamber
e
Comparing the response of a set
response at low energies, and
of TLD's exposed to a NBS-
were used to detect possible low-
calibrated 6065 source to that
energy radiation fields by comparison
obtained from the calibration
with the LiF readings.
source
The LiF and
CaF, chips were matched to 5% and
The calibration is known within + 3%
4% respectively within each batch.
at one standard deviation.
The TLD's were annealed on the atoll
We stored a set of control TLD’s
immediately before being placed on
in a lead pig on a "clean" island
the two islands.
in the Marshalls during the
Two Lawrence
Livermore Laboratory (LLL) plastic
personnel badges containing three
LiF and three CaF, chips were placed
at each field location.
The TLD
packets were attached to trees by
nylon straps or placed on wooden
*Reference to a company or product
name does not imply approval or
recommendation of the product by
the University of California or the
U.S. Energy Research & Development
Administration to the exclusion of
others that may ve suitable.