78
1965), the 226p, initially accumulated by coral gradually decays with time
in the sediment column as it is buried, and then later slowly increases to
equilibrium with 2307), and 234y as 2307), grows in from 234),
Thurber et al.
sp. cit.) found that this equilibrium was establisned at a depth of about
24 meters in drilling cuttings from an island at Eniwetok Atoll.
The results of the measurements of uranium and 226p, concentrations in
lagoon surface sediments are shown in Table 13.
Unfortunately, the uranium
analysis made on this batch of samples resulted in low chemical yields and
th e
239+240
Pu background peak, previously described, could not be resolved
and subtracted from the 232) tracer peak; therefore, the uranium concentrations
in Table 13 may be systematically low by up to 10%.
Because the total number
of counts measured in these samples was small (note the concentration
error
term), the uranium concentrations given should be viewed only as preliminary
observations.
Despite the uncertainties noted above, the 238) concentrations
measured (with the exception of the concentration measured at Station B-20)
fell within a concentration range of 0.68-1.2 pCi/g which is similar to the
1.1 - 1.2 pCi/gm values reported in Eniwetok Atoll soil-sediment (before the
beginning of nuclear testing) by Thurber et al. (op. cit.).
The spread of the
uranium concentrations measured is similar to the variations found by other
investigators in different types of carbonate secreting organisms (Sackett,
1972; Sackett and Potratz, 1963).
The distribution of the radionuclide activity ratio
226,.
Ra/-~
,234
“U in several
of these Bikini sediments (Table 13) show significant departure from the value
of 0.09 which is characteristic of recent Eniwetok corals (Thurber et al.,op.
cit.).
With the exception of the intermediate ratio at Station B-3, the sedi-
ments from stations previously found to be outside of the regions of greatest
radionuclide contamination (the stations above the dotted line in Table 13)