216 ANALYSIS OF ALPHA EMITTERS IN THE CORAL, FAVITES VIRENS sometimes coincides with the annual growth bands (No75) but many times shows no cor- relation with the growth bands(Fig. 3), (c) many high alpha emitter concentrations coincide with anomalous regions in the coral such as holes and/orinfilling of other material (Figs. 3, 4 and 5), (d) at least one of the voids contains finegrained chalky material which contains very high concentrations of alpha emitters equivalent to the hottest spots found, (e) although the alpha distribution does not always coincide with coral growth bands, it does correlate with areas which probably represent periods of coral growth interruption. Evidence for this interruption is obtained through thin-section analysis (Fig. 5) where it is seen that wherever there is high alpha-emitter concentration the coral structure is interrupted by a layer of unidentified skeletal debris with an algal or bryozoan like texture (J. Carew, personal communication). DISCUSSION It is difficult to compare quantitatively results by this and the radiochemical method since it is almost impossible to obtain an average alpha concentration in a large volume of coral using the alpha-track technique. The lowest limit of detection using the track detectors is 50 pCi/g of alpha emitter in 1 ug of calcium carbonate. Since the average activity in the 1954-1955 growth section obtained by chemical analyses was 60 pCi/g (Table 1) we have no way of assessing if these “hot spots’ account for most of the activity in the growth section (being diluted with very low activity coral to average 60 pCi/g) or, at the most, only 20% of the alpha activity in the growth section. To arrive at this latter figure of 20%, we need only assume the majority of the average 60 pCi/g alpha activity (at the 50pCi/g level) determined radiochemically, would not be detected by the alpha-track technique. The texture of material containing the higher levels of alpha radioactivity closely resembles the description of the types of smal! faflout particles resulting from near surface and water detonations at Bikini and Enewetak Atoll (Ad60). It is therefore quite probable that a number of the high activity alpha “hot spots’ are merely evidence of small radioactive particulate inclusions con- taining, in addition to alpha active radionuclides, other fission and activation products. These radionuclides accumulated on the coral during periods of nuclear testing and subsequently incorporated by the coral. No such spots are in evidence in any post test year coral growth although plutonium radionucl- ides, other alpha emitters and some long-lived fission and activation products are easily measured in the coral growths by radiochemical techniques (No75). These observations suggest that particulate incorporation by corals occurs during extremely disturbed periods at the Atoll. During the periods of nuclear testing the coral incorporated trace elements, in this case alpha radioactivity, that are associated in large part with particulate debris as well as incorporating dissolved species from the water column. In periods of relative calm (post test years) the quantity of particulate material incorporated by this coral must decrease substantially which also suggests there is little resuspension of the radioactive sediments in the region of the lagoon wherethis coral was obtained. Because of the alphaactivities found in the coral (Table 1), it is very tempting to asso- ciate the “hot spots” with 7**?°Pu and “Pu and *'Am activity. It is unexpected to find high levels of 7°Pb (Po) in the test year growth section; however weare presently in the process of attempting to analyze radiochemically several “hot” areas to determine whatalpha emitters are present and how they are distributed throughout the “hot spot” regions. CONCLUSIONS A quantitative method of non-destructive detection of alpha emitter concentrations in the range of 1.0-1000 pCi/g calcite with a resolution of 5 4m has been developed. The method was used to map the distribution of some alpha emitting radionuclides in the test year growth sections of a coral Favites virens from the Bikini lagoon. This study has shown that application of ° the solid-state alpha track detector method is