SINGLE PARTICLES FROM HIGH-YIELD AIR BURSTS 107 from the straight-line approximation, were calculated. For over 90% of the decay curves, the standard error in the exponent was less than + 3%. The excellence of the curve fit was further demonstrated by the magnitude of the correlation coefficient, which exceeded 0.99 for over 90% of the decay curves. Values of the decay constant were 0.7 to 1.4, with an average value for all shots of 1.10. These variations were found amongparticles of approximately the same size from each shot. There was no correla~ tion between the decay slope and the particle size or the color. A sta- tistical analysis of the variance indicates that a negligible variation can be associated with experimental errors or statistical fluctuations, and it is concluded that the wide variations in the beta-decay rates result from widely varying fractionation patterns among the particles. These distributions appear to be Gaussian and independent of weapon yield. The physical characteristics of single particles can yield information concerning the radiochemical content. Although single-particle beta and gamma decay curves, the beta-energy spectrum (as well as the gamma-energy spectrum), and the activity per unit particle volume can give valuable information from the health-hazard point of view, the radionuclide concentrations as a function of particle size are of prime importance for an understanding of the fractionation process. In any laboratory program dealing with single-particle analysis, it is desirable to provide simple test procedures to select those particles which will yield particles exhibiting the interesting radionuclide composi- tions. A correlation of the radionuclide compositions with the physical parameters of the particles will provide a field test-particle selection procedure. The radiochemical composition of these particles was also investigated, and the program concerned will be reported in the next paper.* *P. Benson, C. E. Gleit, and L. Leventhal, this volume.