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,
fallout fields.
and handearried (by air)
however,
The instrument is,
sensitive to cosmic
After the 3-month exposure
the dosimeters were retrieved
in a lead
econtainer to Livermore for readout.
radiation.
We studied calibration and signal
Further gamma exposure rate
comparisons were made by means of
fading by exposing separate sets of
37
Cs point source before
TLD's to a
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.
The response of LiF is within
The intensity
reproducible exposures.
137
.
.
of the
Cs calibration source was
approximately 1% of being air
determined by
equivalent for a typical environmental radiation field.
e
Using a NBS calibrated Radocon*
chamber
The CaF,:
2
Dy TLD's have an enhanced energy
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
energy radiation fields by comparison
obtained from the calibration
with the LiF readings.
SOUrCE
The LiF and
0
Co source to that
known. .within +
Car, chips were matched to 5% and
The
4% vespectively within each batch.
at one standard deviation.
The TLD's were annealed on the atoll
calibration
is
We stered 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
3%
Livermore Laboratory (LLL) plastic
personnel badges containing three
LiF and three car, chips were placed
at each field location.
The TLD
packets were attached to trees by
|
=
———_
Seared
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 be suitable,