Table 1. Concentrations of §08mAg in Samples from Eniwetok Atolls Date of Bikini and Concentration Location Samples collection of 1°8mAg Eniwetok Atoll Bikini Atoll Bikini Atoll Bikini Spiny lobster (20) * (hepatopancreas) Spiny lobster (3) (hepatopancreas) Spiny lobster (9) (hepatopancreas) Crater sediment August 1964 0.20 + 0.04 + (d.p.m./g dry wt) Atoll June 1969 1.1403 June 1970 0.75 40.15 July 1969 0.09 + 0.05 * No. in parentheses signifies the number of individuals comprising the composite sample analysed. Species: Panulirus sp. { Errors represent the 67°% confidence level of the count rate measurements. The sediment (Table 1) was taken from the site of a large thermonuclear detonation in 1954 (Bravo Crater), the crater of which is exposed to both lagoon and sea water and which is therefore a source of 1°*™Ag for the biota of the area (1)°"Ag having largely decayed between 1954 and 1969). Thermonuclear tests at other sites in the atoll have also produced silver radionuclides. The last test at Bikini was in 1958, yet we have measured a '!°™Ag concentration of 5.2+0.06 d.p.m./g of soil on Eninman Islet at the atoll and thus the amount of 1°8™Ag present in the Pacific Ocean and elsewhere as a result of pre-1959 testing may be significant. The second observation about the initial production activity ratio of 11°™Ag/'°8™Ag in ref. 1 may be conservative in its estimate of '°®™Ag production. As we have said, the initial activity ratio of '!°™Ag/'°8m™Ag was assumed to be due only to thermal neutron activation of stable silver. There are other production mechanisms for these two radionuclides, the most notable being (n,2n) reactions on stable sifver (1°8™Ag) and (n,p) reactions on stable cadmium ('°8™-11°™Ag), The cadmium react- ion is probably not important because the quantity of stable cadmium in nuclear devices would probably be kept to a minimum on account of the large thermal neutron cross-sections. The excitation functions for (n,p) reactions at atomic weights between 100-110 and neutron energies between 10-20 MeV (ref. 4) are small (1-100 mijlibarns) by contrast with the excitation functions for (n.2n) reactions at atomic weights > 100 and similar neutron energies, which are significantly higher (> 1 barn). cm nee a