Soil samples taken on Bikini showed greater than 95% of the exposure
rate to be due to the !37Cs and thus the reduction in exposure rate can be
assumed to closely follow the decay of !27Cs.
Soil samples from the
other islands showed varying amounts of ©°€o and !92MRh in addition to
the '37Cs.
The reduction in exposure rate due to radioactive decay on
these islands should be much more rapid than for Bikini.
Comparing the
decay curves for these islands with that for Bikini, it can be seen that
within approximately ten to fifteen years only Eneman will have an external
background higher than that of Bikini.
It is recommended that a re-survey
to verify this projection be conducted in about ten years in anticipation
of unrestricted use of the atoll.
In the meantime, the recommendation
of the Ad Hoc Committee that occupancy of the above islands be limited
to visits of short duration should be followed.
The remaining islands of the atoll are Tower in radiation levels than
Bikini and should not be restricted against continuous occupancy on
that basis.
This is particularly true of the Oboe (Aerokoj), Peter
(Aerokojlul), Roger (Bikdrin) complex where the lowest levels on the
atoll were found.
In addition, coconut samples from Aerokoj were lower
in !37Cs and 9°Sr content than those from Bikini or Eneu.
development of these islands should be encouraged.
Agricultural
While the external
levels on Sugar (Lele) are as low as those on the other three islands,
the fact that it is contiguous with Tare (Eneman) would make it advisable
to restrict the use of this island at the present time.
The causeway
joining Lele to Bikdrin makes a logical dividing line for indicating
this restriction.
Sampling of food items presently growing on the atoll indicated mean
concentrations of 137Cs and 29Sr which are essentially in agreement
with those obtained in 1967.
It should be pointed out that the planting
of new species of foods on the islands will require additional sampling
at the time of their reaching maturity in order to assess the potential
internal dose.
Internal dose estimates have been performed by Gustafson!)
utilizing the 1967 data and would appear to be valid for the 1969
data as well.
Results of the 1970 survey for plutonium in air are
approximately two orders of magnitude below the FRC guide for an individual
WM bobs
43