-ll- basis of the average amount of Sr99 in the 44 specimens collected during the. first 50 days following Nectar, less the amount present before Nectar. The relative radioactivity of the two isotopes was calculated from their specific activities. A theo- retical decay curve was then calculated for the combined gr89, sr2%+ xy? contributed by the Nectar test and the sr994 x0 residual from prior tests. Figures 4 and 5 show the actual values superimposed on this theoretical curve. Although there were no specific radiochemical determinations early in the pertod following Nectar it is' reasonable to assume that the exoskeleton has a high degree of selectivity for strontium and that equilibrium must be reached within a few days at most. The assumptions are further supported by decay curves which approach the theoretical curve (Fig. 4). The relatively low levels of activity at 145 days postNectar are a reflection of a change in ratio of ash weight to wet weight; Figure 4 represents the data on an ash weight basis. The change in ratio may be associated with molting, but observations were not made at frequent enough intervals to confirm or deny such an association. - DOE ARCHIVES Contributions of radiostrontium to the crab skeleton at Belle Island from past tests at Eniwetok and Bikini are represented in Figure 5. The pre-Mike level is an approximation since it is based on a single specimen and there was, unfortunately, no biological survey during the 1950 tests. were derived by the method outlined above. The pre-Nectar curves The Mike test contrib: uted about twice as much activity as the Nectar test; fallout from