CHAPTER 17 as "drops of saturated solution of sodium chloride in water, containing in suspension crystals of sodium chloride and small radioactive spheres .+.-PFanging in eize from about 50 to 250 microns in diameter." The analysis has aleo indicated traces of sea-bottom material and iron and coral ballast from the shot parge © However, these insoluble materials appeared in sufficiently minute quantities that the fallout could still be characterized as slurry (expected from water-surface bursts) and not as solid-particulate contaminant (characteristic of land-surface bursts), which leaves a visible residue. The deposited material fram underwater bursts in deep water is expected to be very similar to that from water-surface bursts. If the buret involves a ship, the fallout particles would probably include vaporized ship materials, while if the burst were in shallow water, ocean-bottom materials would be included in the fallout particles, which might leave a visible residue. Tests have indicated®! that washdown removes the “wet mist" type of fallout more effectively than the particulate type. 17.6.2 Weapons-Test Data for Unshielded Locations 1. Water-Surface Bursts Operation Castle: Efforte were made to document the characteristics of the radioactive fallout resulting from three of the lagoon barge shots of Operation Castle. Gamma dose rates at 1 hr at the islands close to surface zero were estimated®to be as high as 4700 r/hr for Shot 2, 440 r/hr for Shot 4, and over 1000 r/hr for Shot 6. Insufficient fallout materiel from Shots 4 and 6 was gathered in the close-in incremental fallout collectors for a meaningful particle analysis; however, con- siderable activity was exhibited by the liquid samples gathered in the 30-min collectors at Shot 4.© at Shot 2, millipore filters exposed topside on the YAG 39 test ship were intensely radioactive and indicate that the activity probably arrived in the form of liquid droplets.© It waa estimated that the fallout from Shot 2 arrived as a fine mist at the stations 50 nautical miles downwind, since the identification flags on the free-floating sea stations were more highly radioactive than the total faliout collections at the same stations. A moist fallout would be absorbed by flapping flags more easily than a dry particulate. 4 Except for patches of chalky substance (of high intensity) on the windward surfaces of aircraft on the YAG 4O test ship, following Shot 2, no visible deposited material was found on the test ships. However, fallout was collected on special filters and on a film by electrostatic precipitation. Studies of the filters and film and their autoradiographs showed that the fallout consisted of microscopic solid crystals and small droplets. Small particles less than 10 microns in diameter appear to have arrived at the earth's surface in the solid or semiliquid state; in we 7 BEST AVAILABLE COPY neeee 7-7) ee ee ee eer ee