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