133 The scintillations produced in the ZnS screen were counted with a “y.g-inch photomultiplier tube coupled to a linear amplifier and scaler. The counting efficiency for the ZnS screen is 47% based en a weightless source calibration.“ The contributicn of (eosr) beta particles to the observed count rate was measured to be negligible. The mean backsround count rate was .033 cpm, which was usually negligible. LPPLICATIONS Rapid Estimation of Total Alpha Radioactivity. At the beginning of the program, only limite¢ knowledge of the relative abundances (hence ranges) of the various alpha-emitting radionuclides was available for the coralline Bikini matrix. An empirical self-absorption correction method was developed using a “standard coral sediment collected in the Bravo Crater. By plotting the net count rate (cpm/mg) of several different thicknesses (expressed as mg/cn”) of this standard sample on semilogarithmic paper, an empirical self-absorption relation was developed (Appendix figure 1). By assuming that the observed dependence was indeed log normal, the slope of the best fit straight line can be used as a mass attenuation coefficient.> The absolute activity of any other sample was then obtained by correcting the count rate (cpm/ma) to zero thickness (i.e. no self-absorption), using the slope of the standard sample by assuming the relation: OF rank Ryan, LRE Memorandum, 6 Cctober 1°72.