(ian CWLR - 2059 - MECHANISM OF FALLOUT PARTICLE FORMATION I (U). Robert C. Tompkins and Philip W. Krey, 27 November 1956. SECRET~RESTRICTED DATA, Technical Report (u) Radiochemical data from Operation CASTLE are applied to the development of a mechanism of fallout-particle formation. The relationships between activity concentrations of several fission products and particle size in fallout from Bravo Shot are studied in detail. Emphasis is placed on those aspects which relate to the mechanism of particle formation. Results of microscope studies are also included, (u) Much of the active fallout below 300u from Bravo Shot reached the ground as loose agglomerates of fine particles. Below 50u, these agglomerates were broken up in the sample processing so that the unit particles could be investigated. (U) Below 50u, activity concentrations in the unit fallout particles could be represented by a relation of the type: Am = ad (u) Where A is the activity concentration of a given nuclide in the active particles at zero time, in microcuries per milligram, d is the particle diameter, in microns, a is a characteristic constant for each nuclide,mdg is indicative of the location of the activity in or on the particles, (uv) Activity occurred in three different ways in the Bravo particles: 1. More or less uniformly on the surface because of late Fgndensa- (ae Op ymustises with long-lived gaseous precursors, e.g., Sr 9, Bat = -l). 2. Randomly on the surface because of scavenging of fine active particles by large inert particles swept through the early cloud. Most of the ective particles larger than 300u were of this type. 3. Throughout the voluges cote Ge. concentrated toward the center of the particles, e.g., Mo, @€0o). In the case of a high yield, surface-land detonation, it seems improbable that the lower portion of the colum, from which a base surge might form, is appreciably contaminated. .