Chapter | INTRODUCTION 1.1 OBJECTIVES The general objective was to collect and correlate the data needed to characterize the fallout, interpret the observed surface-radiation contours, and check the models used to make predictions, for Shots Cherokee, Zuni, Flathead, Navajo, and Tewa during Operation Redwing. The specific objectives of the project were: (1) to determine the time of arrival, rate of arrival, and cessation of fallout, as well as the variation in particle-size distribution and gammaradiation field intensity with time, at several points close to and distant from ground zero; (2) . tocollect undisturbed samples of fallout from appropriate land- and water-surface detonations for the purpose of describing certain physical properties of the particles and droplets, including their shape, size, density and associated radioactivity; measuringthe activity and mass deposited per unit area; establishing the chemical and radiochemical composition of the fallout material; and determining the sizes of particles and dropiets arriving at given times at several important points in the fallout area; (3) to make early-time studies of selected particles and Samples in order to establish their radioactive-decay rates and gamma-energy spectra; (4) to measure the rate of penetration of activity in the ocean during fallout, the variation of activity with depth during and after fallout, and the variation of the gamma-radiation field with time a short distance above the water surface; and (5) to obtain supplementary radiation-contour data at short and intermediate distances from ground zero bytotal-fallout collections and time-ofarrival measurements. It was not an objective of the project to obtain data sufficient for the determination of comPlete fallout contours. Instead, emphasis was placed on: (1) complete and controlled documentation of the fallout event at certain key points throughoutthe pattern, also intended to serve as correlation points with the surveys of other projects; (2) precise measurements of time- dependent phenomena, which could be utilized to establish which of the conflicting assumptions of various fallout prediction theories were correct; (3) analysis of the fallout material for the primary purpose of obtaining a better understanding of the contaminant produced by water-surface detonations; and (4) gross documentation of the fallout at a large numberof points in and near the lagoon. 1.2 BACKGROUND A few collections of fallout from tower shots were made in open pans during Operation Greenhouse (Reference 1). More extensive measurements were made for the surface and underground Shots of Operation Jangle (Reference 2). Specialized collectors were designed to sample incre- mentally with time and to exclude extraneous material by sampling only duringthe fallout period. The studies during Operation Jangle indicated that fallout could be of military importance in a- reas beyond the zones of severe blast and thermal damage (Reference 3). During Operation Ivy, a limited effort was made to determine the important fallout areas for a device of megaton yield (Reference 4). Because of operational difficulties, no information on