C.
Table 3.
Case
Estimated mean exposure rates (uR/hr) used for the dose calculations.
Village island
Village
Interior
Beach
Lagoon
Other islands
4
4
1
3.5
50
5
‘5
3.5
3.5
42
42
1
Eneu
2
3
thee
Bikini
Bikini
24 a
242
42 b
42°
4
Bikini
34°
42>
5
3.5
42
5
Bikini _
53°
41°
5
3.5
- 42
6
Bikini
53°
4y®
5
3.5
42
.
4includes area 1 in Fig. 4.
Pincludes areas 3 and 4 in Fig. 4.
“mcludes area 2 in Fig. 4.
dincludes area 3 in Fig. 4.
© Includes area 4 less area 3 in Fig. 4.
0.2 uR/hr due to naturally occurring radionuclides in the sea water.
Cases.3 and 4
demonstrate the effect of remedial action on reducing the gamma exposure rates.
Since the people spend a considerable fraction of their time in the immediate
vicinity of their homes, it appears that it may be feasible to take certain remedial
_ actions to reduce the exposure rates in this area.
For instance, placing 5 cm of clean
coral gravel around the houses out to a distance of 10 m, a common practice in the
Marshall Islands, will reduce the exposure rates by a factor of 2.
Removing andre-
placing with clean soil the top 20 cm of soil out to a distance of 10 m from the houses
will reduce the exposure rates by a factor of 8. In addition, the shielding prévided by
the houses themselves will reduce the exposure rates by a factor of 2.
Mixing or over-
turning of the topsoil will most likely not be effective since the soil has already been
thoroughly disturbed by the agricultural rehabilitation activities.
Basedupon the data of Bennett and Beck,” it appears that it may be reasonable to
assume, for dose prediction purposes, that the gamma exposure rates on the islands are due
to 1%¢s and 6%, activities with respective contributions of 80% and 20%.
This
assumption will be reexamined by means of the gamma spectral analyses of the soil samples
collected during this survey.
Using this assumption and the information presented in
Tables 2 and 3, we calculated the integral first-year and 50-year whole-body external»
gamma-ray doses for each age group for each living pattern presented in Table 1. The
results were then combined by "folding in” the present population distribution.
The
effect of radioactive decay was included in the calculation; however, the additional
reduction in.exposure rates due to possible weathering or agricultural crop production
processes was not included.
Lo
-7-
a