An evaluation of activated bismuth isotopes in environmental samples from the former Western Pacific Proving Grounds

Bi-207 (T-1/2 = 32.2 y) was generated by activation of weapons material dur ing a few "clean" nuclear tests at the U.S. Western Pacific Proving Grounds of Enewetak and Bikini Atolls. The radionuclides first appeared in the Ene wetak environment during 1958 and in the environment of Bikini during 1956. Crater sediments from Bikini with high levels of Bi-207 were analyzed by g amma-spectrometry in an attempt to determine the relative concentrations of Bi-208 (T = 3.68.10(5) y). The bismuth isotopes were probably generated du ring the "clean", 9.3 Mt Poplar test held on 7/12/58. The atom ratio of Bi- 208 to Bi-207 (R value) ranges from similar to 12 to over 200 in sections o f core sediments from the largest nuclear crater at Bikini atoll. The prese nce of bismuth in the device is suggested to account for R values in excess of 10.