UNCLASSIFIED INTRODUCTION Some of the nuclear devices fired in Operation REDWING during the Spring of 1956 at the Eniwetok Proving Ground were detonated on or near the surface of the lagoon water. Up to this time, only limited data had been gathered on the physical-chemical-radiological properties of individual fallout particles from such bursts. Therefore, two events, Flathead and Navajo, were selected as subjects for an extensive fallout study. The nuclear devices fired were situated on steel barges anchored in relatively deep lagoon water. The principal sources of material expected to comprise the fallout were the barge complex, the surrounding seawater and perhaps some lagoon bottom solids. It was hypothesized that sea salts would constitute the major portion of any fallout. With this in mind, a special reagent film!, quantitative for submicroscopic amounts of chloride, was developed. Since sea salts are hygroscopic, it was felt that the fallout particles would pick up atmospheric water and arrive at the sampling stations as slurry-like droplets. Therefore, the reagent film was calibrated to measure this water content.” The influence of the barge complex on particle composition was unassessed prior to the Operation. Sampling stations were located at varying distances from the shot points. These stations were aboard anchored barges, type YFNB, and manned ships, type YAGand LST. An array of specialized sampling devices was located at each station. Particles collected in the incremental type of collector, 354 were used for these fallout studies. Since this de- vice sequentially exposed trays containing chloride reagent film, particles could be classified by time of arrival. One of the ship sampling stations was connected by an elevator device to a radiation-shielded laboratory, permitting almost immediate examination of fallout samples. METHODS OF ANALYSIS The analytical methods developed were so devised that the physical, chemical, and radiological properties of the individual particles could -l- Ra es i: bi ra Pi FA to ny rs Ped ae me pea pal md UNCLASSIFIED