Conclusions
Previous soil surveys indicated the primary radioisotopes contributing to the
external
does rate are
137
Cs and
contribution (EN73, p. 103).
60
Co for gammas, and
90
Sr for beta
External dose estimates for future inhabitants
were based on aerial gamma surveys and did not include beta contributions and
shallow dose estimates.
The major finding of the work reported herein is that
approximately 29% of the total external dose rate on Enewetak Atoll] is due to
beta or low-energy gamma radiation.
While marked deviation from 29% can be
found, especially at locations with little or no vegetation, the beta
contribution is surprisingly insensitive to extent of ground cover typically
found on these islands.
The impact of such a significant fraction of the total external dose rate
resulting from beta or low-energy gamma radiation is illustrated in Table 1,
where integral 30-year shallow dose estimates are compared with 30-year whole
body doses reported in the 1972 survey.
Living patterns and external dose
estimates represent assumptions of village location, visitation, and
agriculture patterns (EN73).
the map in Figure 1.
They are listed in Table 1 and can be located on
Living patterns I and II are for residence in the
southern islands, and patterns III through VI are for residence in the
northern part of the atoll.
External dose rates are much lower in the
southern part of the Atoll.
The living patterns include approximately 20% of
the time spent on other islands for agricultural purposes, except for pattern
III, in which residence, visitation and agriculture are confined to one island.
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