RADIOCHEMICAL FRACTIONATION CHARACTERISTICS OF SINGLE PARTICLES FROM HIGH-YIELD AIR BURSTS P. BENSON, C. E. GLEIT, and L. LEVENTHAL Tracerlab, A Division of Laboratory for Electronics, Inc., Richmond, California ABSTRACT The radiochemical fractionation characteristics from two Operation Dominic high-yield air bursts were studied. Particles measuring from 2.9 to 20.0 u were isolated from filter-paper matrices by autoradiographic registration and confirmed by optical microscopy. After physical measurements radiochemical and/or gamma-spectroscopy studies were performed on individual and aggregates of particles. Of particular interest was the distribution of volatile and refractory nuclides for each particle size. The nuclides radiochemically analyzed were *°Mo, 8Sr, Sr Zp 128m 132P7— 1icg MB,Mice Moe Ming %37y, and 239Np, Gamma-spectra analysis was used to determine the Zr andBa con- centrations in 334 particles, A computer technique for resolving these nuclides and Mo, !Ru, 41,Te, "cs, Mice, M4ce, ’Nd, and9Np was developed. The particles were found to be extremely fractionated. A logarith- mic fractionation correlation plot for °Ba was determined which com- pared within the limits of error with data plotted by Freiling for high- yield water bursts. The logarithms of ™Zr and '°Baactivities were plotted as functions of the particle diameters for the two shots. The slopes for the regression plot for Zr were 3.41 + 0.18 and 3.09 + 0.37. These values imply a cubic relation. The slopes for the regression plot for “°Ba were 2.63 + 0.24 and 2.32 + 0.50, somewhat between a square and a cubic relation. These results point toward condensation of the re- fractory nuclides initially with subsequent precipitation of the volatiles on the particles at later times. 108