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Two of the largest northern islands (Enjebi and Bokambako) were used for this
study because of their higher soil radionuclide concentrations and the
potential use of Enjebi as a residence and agricultural island.
Comparative
beta and gamma dose measurements were made at a total of 87 locations on these
two islands with thermoluminescent dosimeters, pressurized ionization
chambers, portable sodium iodide detectors, and pancake GM probes.
Locations
were carefully selected to represent a wide range of exposure rates and
variety of ground cover.
Measurement Methods
A portable instrument with a 2.5 cm diameter x 3.8 cm Nal crystal and
ratemeter readout was used primarily for selection of measurement location.
External exposure rate measurements were made at a height of 1 meter at 67
locations with a pressurized ionization chamber which consists of a stainless
steel sphere filled with high pressure argon, connected to an electrometer
with digital readout.
Calibration of this instrument was verified by DOE
laboratories prior to the survey.
Although insensitive to beta or low energy
gamma radiation, it is sensitive to cosmic radiation.
It has a relatively
flat energy response over the gamma ray energy range encountered in this
survey (NA75).
The primary technique used to determine beta or low energy gamma contribution
to the external dose rate was measurements made with thermoluminescent (TLD)
dosimeters.
LiF(TLD 700) previously matched to within
+2% were used.
The
dosimeters were annealed at Enewetak Atoll immediately prior to placement on
the two islands.
Three TLD dosimeters were placed in the Lawrence Livermore
National Laboratory (LLNL) personnel dosimeter badge with a blank badge
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