4.2 RECOMMENDATIONS The ratio of local to worldwide 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 apprectable fallout haa occurred, and by 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 woridwide fallout from particulate samples are: (1) the particle size at which division into local and worldwide fallout occurs for each sample, (2) the fraction of the volume of the cloud swept out, in obtaining each sample, (3) the mass of each of the two groups of particles in each sample, and (4) the R-values of the radionuclide of interest in each of the two groups of particles in each sample. The first of these can be calculated in advance from the criteria for worldwide fallout from the altitude of sample collection. The second can be calculated from the area of the sampling system by obtaining the total volume of the cloud and the cloud dimensions at various altitudes from cloud photography. The third can be obtained by separating the particles into the necessary two fractions during sampling and subsequently weighing each group. The fourth can be obtained by radiochemical analyses of each of the two particle groups. It is recommended that such a program be carried out if the opportunity is presented by future nuclear tests. ,