214 ANALYSIS OF ALPHA EMITTERS IN THE CORAL, FAVITES VIRENS Fic. 4. Distribution of alpha-emitters in three thin slabs cut perpendicular to surface shownin Fig. 2. Scale is 1:1 (reflected light). perpendicular to the surface A and shownin Fig. 4. The thin sections were covered by a Kodak film and after 30 days exposure the cellulose nitrate films were etched, studied and then replaced on to the coral thin section as close as possible to the same position as during exposure. This allows correlation between the alpha emitter location and specific petrographic features to within 5 wm. Figure 5 shows the results for thin section C. In actual practice the cellulose nitrate films and the thin sections were observed through the microscope simultaneously. At low magnifications both thin section and cellulose ’ nitrate film were in focus, at high magnifications only one surface at a time could be focussed upon. In material of the absolute fraction of alpha activity associated with the “thot spots”, it is apparent that all the alpha activity within the coral is not homogeneously distributed. Rather, an analysis of the alpha “hot spots” in the 1954-1958 test year growth sections Fic. 3. Concentrations of alpha-emitters in a portion of the coral Favites virens slab (see Fig. 2). : boundary of areas counted. pCi/g less than 2, (a) 2-9, (b) 10-24, (c} 25-49, (d) 50-74, (e) 75-99,(f) 100~149, (g) 150-155. show: (a) some of the alpha emitters are concentrated in small discrete ribbons rather than in broad bands, (b) the distribution alpha emitter