212 ANALYSIS OF ALPHA EMITTERSIN THE CORAL, FAVITES VIRENS 2 and 15 wm were prepared by allowing calcite particles from a calcite suspension (particles less than | «4m in diameter) to settle on the Kodak film. The thicknesses of the calcite were calculated by weighing the CaCO, (density of 2.7 g/cm’) deposited on a known area of Kodak film. It is assumed that the stopping powerof the air between the calcite grains is negligible. The curve labeled ‘‘Calcite’ in Fig. 1 has been determined in this manner. The overlap of the two curves in Fig. 1 indicate that the relative stopping power of calcite to polycarbonate is about 2:1. It can be calculated (Fig. 1) that 1 track/0.04 mm?/30 day exposure is equivalent to 130pCi/g when calcite is the energy degrader. Comparing this result to the value of 104pCi/g for one track/0.04mm7/30 day exposure obtained from the polycarbonate experiments we find a difference of about 30%. The coral analyzed is aragonite; however, the calibration using calcite does not introduce significant error considering the other inaccuracies. (b) Calibration of the Kodak film by use of coral with known alpha emitter concentration. An independent methodfor calibration of the Kodak film was accomplished by using a standard of known alpha emitter concentration in a calcium carbonate matrix (a powdered coral). The powdered coral sample contained 166+9pCi/g of plutonium and americium radionuclides consisting of 101+ 7 pCi/g of “Pu and Pu, 55 +5 pCi/g of 7*Pu and 10.442 pCi/g of “'Am. Batch A and Batch B of Kodak film LR-115 were exposed for 30 days to aliquots of this powdered coral sample giving a value of 174+ 17 pCi/g based on Batch A polycarbonate calibration and 160 + 9 pCi/g based on Batch B polycarbonate calibration. Both these values are within the precision (166+ 9) reported for the chemical method. One track/0.04 mm?/30 day exposure is taken as equivalent to 40 pCi alpha emit- ters/g-calcite for Batch’ A and 100 pCi/g for Batch B for all analyses discussed in this report. In contrast to the radiochemical data reported for this coral (No75) the activities reported here are not corrected for decay because concentration data on each in- dividual radioactive isotope is not obtained by the solid-state track detection method. RESULTS (1) Analyses of slabs of the coral The first attempt at defining the alpha emitter distributions and concentrations by applying the solid-state track detector to a section of coral sample was done by using a slab of coral. The section selected contained the 1954-58 annual growth rings (No75). Cellulose nitrate film was applied directly to the slab and to three additional sections cut perpendicular to it (Fig. 2) and left for 30 days exposure. The analyses of detectors exposed to both sides of the slab show the following results (Figs. 3 and 4): (a) Some of the alpha emitters in the 19541958 growth interval are concentrated in small volumes coincMing with damaged regions and holes in the coral texture (Figs. 3. 4b and c). (b) “‘Hot spots” occurring in the coral growth bands equivalent to the years 1954 and 1956 are located within 4mm?’ (Fig. 3). One “hot spot’ was detected in a region of the coral we were unable to date using the annual band technique (No75) but it was apparently in a period of growth before 1954. It is possible that this spot designates the 1946 growth (the first nuclear test year at Bikini} but we cannot rule out possible chance contamination of the area during cutting operations. (c) No “hot spots” were found on detectors exposed to post test year growth sections of coral. (d) An alpha concentration of 800 pCi/g was obtained on very fine grained chalky material scraped from a void within the coral. (e) A maximum concentration of 720 pCi/g was measured in 0.04 mm’ of the 1954 growth band. This is an equivalent to 0.7 fCi of alpha activity. (2) Analyses of the thin sections of the coral To define more clearly the relationship between the coral fine structure and the alpha emitter locations, uncovered thin sections of the coral were prepared from the slabs cut