0018933 3- Radionuclide fractionation is pronounced in shots over a coral land surface. The local fallout is depleted in both sr?9 and cs¥7, while the upper portions of the clouds are enriched. Fractionation is much less for water surface shots. 4. Nuclear clouds are non-uniform in composition and certain nuclide ratios vary by rather large amounts from top to bottom. Again, this is much larger for land than water surface detonations. 5. The radiochemical studies of fine and coarse particles indicate that the fission products with rare gas precursors, sr®? | sr70, y71, and csi37 are in general more concentrated in the fine particles in the land and reef shots. In the water surface shot they appear to be more evenly distributed among the particle groups. 6. sr? ana cst? distributions computed from cloud and fallout data are roughly in agreement with one another. 4.2 RECOMMENDATIONS The ratio of local to world-wide fallout is essentially governed by the distribution of particles with respect to size and altitude in the cloud at stabilization (i.e. at an early time before appreciable fallout has occurred), and the specific activity of radionuclides of interest as a function of particle size. The latter function may vary with altitude in the cloud at stabilization. The basic types of information necessary to calculate the fractions of a given radionuclide in local and worldwide fallout from particulate samples are: 1) the particle size at which division into local and worldwide fallout occurs for each sample