Nuclear weapons produced U-236, (PU)-P-239 and Pu-240 archived in a Porites Lutea coral from Enewetak Atoll

摘要

A slice from a Porites Lutea coral core collected inside the Enewetak Atoll lagoon, within 15 km of all major nuclear tests conducted at the atoll, was analysed for U-236, Pu-239 and Pu-240 over the time interval 1952-1964 using a higher time resolution than previously reported for a parallel slice from the same core. In addition two sediment samples from the Koa and Oak craters were analysed. The strong peaks in the concentrations of U-236 and (PU)-P-239 in the testing years are confirmed to be considerably wider than the flushing time of the lagoon. This is likely due to the growth mechanism of the coral. Following the last test in 1958 atom concentrations of both U-236 and (PU)-P-239 decreased from their peak values by more than 95% and showed a seasonal signal thereafter. Between 1959 and 1964 the weighted average of the Pu-240/Pu-239 atom ratio is 0.124 +/- 0.008 which is similar to that in the lagoon sediments (0.129 +/- 0.006) but quite distinct from the global fallout value of similar to 0.18. This, and the high (PU)-P-239,240 and U-236 concentrations in the sediments, provides clear evidence that the post-testing signal in the coral is dominated by remobilisation of the isotopes from the lagoon sediments rather than from global fallout. (C) 2017 Elsevier Ltd. All rights reserved.