-29-
Considering the atoll as a whole, and the three successive test
series, the evidence from Figure 8 suggests that the 1956 series con-
tributed to the plankton not more than 1/100 as much radioactivity as
the original 1954 fallout, and the 1958 series, not more than 1/20
as much as the 1956 series.
It is further concluded that the northern
part of Rongelap Atoll received a heavier fallout from the March 1,
1954 detonation at Bikini than did the southern part.
In contrast, the
relatively slight fallout from later detonations affected the southern
more than the northern parts of the atoll, as is evidenced by the higher
levels of radioactivity in the plankton of the lagoon at Rongelap Island
than at Kabelle Island.
Bottom Samples
Results of beta counting of lagoon bottom samples collected in
August 1958 at the stations shown in Figure 7 appear in Table 5 and
Figurel0. Sample values ranged from .051 to .28, with a geometric
mean of .089 uc/kg of ash.
Ashing changed wet sample weight by an
average factor of 0.47, which included the natural organic matter and
the soap.
The soap contained 21 per cent ash.
The highest concentrations of activity occurred at Stations 5 and
6, north and west of Eniaetok Island.
Analysis of the samples from the
anchor at Station 10 showed that the radioactivity was not confined to
the top inch or so of the bottom material, but that it penetrated to
a