- Results of Gamma-Ray Exposure Rate Measurements
\
The geographical variability of
vertical coordinate is a measure of
the gamma-ray exposure rates for
the gamma exposure rate.
Bikini and Eneu Islands is shown in
elevated irregularly shaped areas
Figs. 4 and 5.
appear as "peaks" while the lesser
The contribution due
Thus, the
to cosmic radiation has been sub-
values near the shores appear as
tracted.
relatively low flat areas.
On Bikini Island the
Note
individual measurements from which
especially the low flat area
the contour levels were derived are
Situated on the ocean side near the
listed in the Appendix.
center of the island (Fig. 6a)..
Note the
complex patterns displayed throughout
the island.
The gamma exposure rates
This complexity may be
measured on Eneu Island (Fig. 5) show
due, in part, to the inhomogeneity
that the island is characterized by
in the original fallout pattern
low (less than 10 —uR/h) and more or
produced by the Bravo event, but it
less uniformly distributed gamma
certainly reflects the extensive
radiation levels over the entire
earth moving activities performed
island.
These total gamma-ray exposure
over the entire island as part of
the agricultural rehabilitation
rates are the basis for the external
program.
dose estimation.
The exposure rates near
However, to deter=
the shores are typically of the
mine the annual dose and dose
order of 10 to 20 uR/h, while the
commitment, it was also necessary
elevated interior values vary over a
to determine the fractional contri-
wide range of roughly 30 to 100 UR/h.
bution made by the predominant
The interior portions of the island
gamma-emitting radionuclides distri-
may be visualized as having a general
buted in the soil.
background of about 30 to 40 uR/h with
experience at Enewetak Atoll and
numerous irregularly shaped areas
the data of Bennett and Beck?
exhibiting elevated levels superim-
obtained during the 1967 Bikini
posed in a random fashion over this
Survey, we expected that the
general background.
primary contribution to the gamma
This may also be
visualized by viewing the three
dimensional computer generated
Based on our
exposure rates would be due to
.137 Cs and 60 Co activities in the
graphical displays of the exposure
soil.
rates (Figs. 6a, b and c).
gamma emitters such as
The
-~7-8-
Trace quantities of other
125
Sb