AOS aay PRELIMINARY TEST OF RADIOACTIVITY IN COCONUT CRABS AT ENIWETOK ATOLL COLLECTED IN 1972 PROCEDURE Samples of skeleton and muscle from two specimens of coconut crabs (Birgus Jatro L.) collected on 21,January 1972, Glenn Islet, Eniwetok were dried, pulverized and placed in liquid scintillation vials with Insta-Gel as a suspending and scintillation medium. These samples were compared with similar tissues from the crab Pachygrapus crassipes collected near Laguna Beach, California in June 1972. These latter specimens are assumed to not contain significant amount of radioactive nucleides. Table | gives a description of the samples. Samples were compared using a Packard Series 2000 Liquid Scintillation Spectrometer. For total radioactivity a window of 50 (on a 1000 maximum scale) to infinity was used, using the 20, 60, and 80% gain values of the instrument. For characterization of the spectrum a 10% window width (50-150) was employed at various gain teveis. RESULTS Preliminary tests indicated that there is definite excess of radioactivity in the coconut crabs for Eniwetok. However, it is so small that considerable amounts of sample had to be used to permit detection and characterization of the spectral distribution. Tests on the total count are reported in Table !. Analysis of this data also gives considerable evidence of quenching as the weight of the sample used increases. This was tested further (following spectrum analysis) by adding a standard amount of 43cq to each tube. The increase in counts was inversely proportional to the size of the sample. Quenching (in sample 5) was noted to be less pronounced (23% decrease) when a hicher energy nucleide (29s) vias added as compared to a weaker nucleide (153) which showed a 66% decrease. ~ Scintillation vials without any crab tissue present but with a standard amount o 5 90 Sr or 4s Ca were used for comparison. y -