activity between various classes of particles and "dispersed" phases. Since there are distinct differences in track diameter distributions between background tracks and samples with different Ea distributions (see Figures 1-3), one can envision a combination of track position and size analyses which could be used to characterize particle size, activity, and depth within sample. If the sample surface is solid (e.g., resinbedded soil) and the film properly indexed, it would then be possible to locate and retrieve for direct investigation selected “hot spots" (Levy et al., 1977). SUMMARY AND CONCLUSIONS Commercial cellulose nitrate track detectors have some disadvantages: they cannot discriminate well between alpha particles from different nuclides; they require some form of optical readout; and fairly demanding procedures must be followed to maximize sensitivity and reproducibility. However, their advantages are even more persuasive: they provide unique information on spatial distribution of activity; they are adaptable to the study of small and/or inhomogeneous samples (the volume of sample actually sensed by the film for any of the environmental samples in this study was less than 0.1 em3, or a few hundred mg); and, for applications where semiquantitative determinations are adequate, they are fast, cheap, and simple when compared to radiochemical methods. Specifically, the following areas of application appear able to profit from immediate use of alpha track detectors: 1. Analysis of amounts and distributions of activity in small samples such as aerosol filters, specific soil or sediment size fractions or phases, and biological subsamples (e.g., specific organs); 2. 3. Screening of samples from a contaminated environment in order to design the most efficient survey and to target a limited number of critical samples for radiochemical analysis; Research into the statistical basis for sampling environments and analyzing samples with inhomogeneous activity distributions. ACKNOWLEDGMENTS Much of the work described was done while the senior author held a summer research appointment at Lawrence Livermore Laboratory, but addi-~ tional work was carried out at the University of Hawaii under DOE Contract EY~76-S-08-641. We gratefully acknowledge the assistance of all those at LLL and U. of H. who gave willingly of their time and advice. The assistance of Mr. Barry Fankhauser is especially appreciated. 605