102
sediments are also very old.
The ratios
238,),235
Ua
nd 234,,,238
U in the sediments collectec in Zuni
Crater (station C-12) are quite different from any other ratios measured in
tne lagoon.
o30,,,¢355
The low “~"U:“"°U ratio found may indicate a significant enrich-
ment in 2354 (relative to its concentration from sea water) in at least the
surface sediment section of the core.
In addition, the ratio
234.238),
measured in the three sections of the core is higher than the ratio (1.15)
reported to be characteristic of similar coralline sediments.
These "uncommon'
ratios can be explained by enrichments in 235), and 234 U, or by a relative
depletion of
depletion of
238
238
U.
Because of the difficulty in rationalizing a relative
U, a possible explanation is that
fueled with 235 y
234
U was present in a device
The plausibility of such an argument can be based on two
factors: (1) that 234) (as judged from the abundances of uranium isotopes in
235
U enriched N.B.S. reference standards) is concentrated greatly in 2354
enriched uranium, compared to its relative natural isotopic abundance; and (2)
whereas 235y is fissionable, 234) is not commonly so regarded.
Because the
specific activity of 234 is 2.9 x 103 times greater than 2354 fission of
only 235 U would result in elevated
234.235
U activity ratios in non-fissioned
uranium, and could explain both the anomalous ratios measured.
5.4
Total Alpha Radioactivity
The methodology used for measuring the total alpha radioactivity
of the Bikini sediments is presented in Appendix I.
The samples were pre-
pared with thicknesses Tess than the range of the alpha particles in the
matrix.
The matrix, which is essentially pure CaC03, is constant from sample
to sample.
Self-absorption corrections for each sample were made, using a
relation derived from a standard sample.
The method gives relative activity
concentrations directly, or “absolute” concentrations after a correction for