a ooa620 3 The Problem > The experimental investigations of the effectiveness ané efficiency of decontamination procedures using synthetic fallout ani the operational evaluations of the date require knowledge of the composition of fallout from various conditions of detonation. In the experimental investigations, a realistic range of fallout mess deposits is needed to design experiments in which operationally useful date can be obtained; in this case it is necessary that the simulated fallout be as similer to real fallout as possible. Knowledge of fallout composition is also necessary to understand and correlate decontamination data from past field tests with those obtained by use of the simlants. In operational evaluations of decontamination efficiencies, the radiation intensities associated with the fallout mass ani radioactive elements is needed to estimate the true reduction in dose that is associated with the effici- ency of a decontamination procedure. No methods are presently available for estimating the composition of fallout and no summary of the available data has been previously made. The Findings poE/NU The mass contour ratio, defined in mg/sq ft/r/br at 1 br, and the fraction-of-device contour retio, defined in r/br at 1 br x(sq ft)-l, are first discussed in terms of ideal explosion coniitions in which all the activity produced is mixed uniformly with the crater mass and is deposited uniformly over an ideal plane. In this case, a single value of each contour ratio results for a given detonation. Discussion of the effect on the idealized contour ratios of weapon yield, type of weapon, height or depth of burst, fractionation, distance frem ground zero, instrument response, and terrain roughness lead to the following general relationship of