118 BENSON, GLEIT, AND LEVENTHAL Although the surface relation between MR, activity and particle size cannot be demonstrated on the basis of these data, the variance in the activity per unit area is quite obvious. One would expect this in nuclear-explosion clouds in which the particles form rather quickly and the volatile constituents precipitate on the particle surfaces muchlater. This hypothesis appears to be confirmed if one considers the Zr as representative of a refractory nuclide. The cubic relation then would indicate that the °°Zr is condensed initially andis distributed as a function of the volume of the particle. In effect, regularity is observed through approximately a hundredfold change in volume. Another interesting observation that stems from a comparison of the shots A and B plotsis that the intercept of the '"Ba regression line of the nuclides of a particular particle size is a function of the yield to mass ratio. CONCLUSIONS The feasibility of isolating and analyzing individual particles by radiochemical and gamma-spectrometric techniques has been demonstrated. Particles under 10 yp and as low as 10° fissions have yielded accu- rate values for the important volatile and refractory fission products. Heavy-element analysis is borderline for *8"U and 7°Np andis de- pendent on analysis at early times. Unless an induced activity is present in abnormally large amounts, the analyses of these radionuclides in single particles are not feasible. Gamma spectrometry is a satisfactory technique for the resolution of nuclides in large numbersof individual particles and may be used to obtain ‘4°Ba and °°Zr values to + 5%. Logarithm fractionation plots of particles from high-yield air tests have been found to correlate well with ryqo,39 and ros gg values from a coral-surface burst and three types of water bursts. Barium-140 fissions have been found to correlate with between a square and a cubic relation to particle diameter. Zirconium-95 fissions have demonstrated a cubic relation to particle diameter. REFERENCES 1. C. L. Carnahan, A Method for the Analysis of Complex Peaks Occurring in Gamma Ray Pulse Height Distributions, Report USNRDL-TR-572, U. S, Naval Radiological Defense Laboratory, July 1962. 2. Tracerlab, A Division of Laboratory for Electronics, Inc., The Analysis of Particulate Debris from Pacific Air Shots, Final Report, Dec. 16, 1964. 3. E.C. Freiling, Radionuclide Fractionation in Bomb Debris, Science 133: 1991 (1961). 4, P.A. Benson, Sixth Quarterly Progress Report to USAEC, Tracerlab, A Division of Laboratory for Electronics, Inc., Apr. 1, 1964. (Classified)