DNA 1240H-2 l. Water-Surface Bursts ation Castle: At Operation Castle, in the Spring of 1954, fallout with very small particle size occurred from the over-water shots. * As @ result, the settling rate was slow, and it is estimated that the depth-of-penetration and below-surface activity measurements were reliable. Following Yankee, Shot 5 at Operation Castle! (13.5 Mr over about 250 ft of water), between H + 6 hr and D + 4 days a fleet tug carrying improvised radiological and oceanographic gear gruised the ocean downwind of Bikini Atoll, taking samples of the water at the surface and to depths of 2400 ft. In addition, gamma-ray dose rates were measured above the sea surface, just below the sea surface, and occasionally to 80 meters (about 262 ft) depth. Measurements were made by three sealed Geiger-counter instruments that were either towed or lowered to various depths at definite points in the area, and by a standard ionizationchamber Radiac termed a "pot," set in a steel tank 6 ft above the sea, and used to monitor the radiation from the surface every 5 to 20 minutes. These measurements indicated that at about 23.5 nautical mi from surface zero and within 16 hr after shot, activity became so concentrated that all the towed Geiger instruments deflected off-scale (range not specified). However, the "pot" instrument set on a scale of O to 50 mr/hr continued to indicate gamma dose rates of about 20 mr/hr (after corrections for drift error). The first depth cast was made at about 50 naut mi from surface zero at about H + 34 hr. At that time, maximum dose rates (in situ) of about 17 m/hr registered fairly uniformly from the surface to depths of about 160 ft. Dose rates then decreased with depth to about 2 mr/hr at a depth of about 260 ft. By H+ 75 hr, at about 140 naut mi from surface zero, dose rates were uniformly between 1 and 2 mr/hr from the surface to depths of about 250 ft. Operation Redwing: At Operation Redwing in 1956, a more elaborate program of radiological measurements of sea water was carried. out. Measurements of early depths of fallout penetration were made”) ® within 15 naut mi of surface zero, and ship surveys after each event involved detailed radiological and oceanographic measurements, including surfaceprobe measurements, over the area of the fallout from both land and ter-surface shots. The fallout from Shots Navajo (a barge shot of about athead and Navajo fallout collected and examined consisted of Slurry particles,™ the inert components of which were water, sea salts, and a small amount of insoluble solids. Average densities of these particles were between about 1.15 and 1.5 gn/cm3. All the active fallout collected at Shot Zuni consisted of solid particles,*‘of average densities between 2.0 and 2.8 gm/cn3, and no slurry was observed. As would be expected by comparing the densities, * References 40, 64, and 76. LAS! I A Y A T BES cc ow " g Sew 17-92 et ee ee ee ee ee es ee ee ee er ee ee ee Y