CHAPTER 17 no shipboard radiation measurements due to contaminated water were obtained because the starting signals were not received on the instru- mented target ships; thus, no comparison is possible between shipboard and water doses for a Wahoo-type shot. Reference 33 concluded that although radiation from the water may have contributed to compartment dose rates at later times, the contribution of contaminated water to the total dose observed aboard the target ships was of little significance. ‘ ration Wi : From Operation Wigwam, little data are available that permit estimation of the contribution of waterborne radiation to shipboard doses. One figure in Ref. 31 gives dose-rate histories at stations below the waterline during the first traverse of the contaminated area by the YAG 40 between 50 and 80 min after burst. Dose rates at the keel station (about 30 ft below the waterline) peaked at about 13 r/hr at about 75 min. At about the same time, dose rates (estimated to be due only to radiation from the water) at station 64 in the Recorder room, peaked at about 0.8 r/hr. This one plot indicates that, for the duration of the traversal of the area, the dose rates at station 64 were only about 6% of those recorded at the keel station. 17.7.5 Summary No contaminated-water dose or dose-rate histories are available at early times near surface zero. for water-surface test shots. Available data indicate that at times of 4 hr and later, the contribution of waterborne radiation to shipboard doses is negligible, tut it is possible that at early times contamination in the water around surface zero could add to the radiation field aboard a ship traversing the area. Analysis>¢ of records of underwater test shots leads to the conclusion that radiation from waterborne radioactive material is significant. There appear to be three major sources of waterborne radiation: (1) radiation from material deposited in the water from the base surge; (2) radiation due to water directly contaminated by the bomb (white water); and (3) radiation due to patches of radioactive foam generated during eruption and collapse of the column or plumes. Radioactive material deposited in the water from the base surge appears to dissipate rapidly after the passage of the base surge, whereas white water may be highly radioactive up to an hour after burst time. Radioactive foam, estimated to be the most important early-time waterborne source, is suspected of causing peak dose rates of 1000 to 2000 r/hr observed in the underwater dose-rate records for Shot Wahoo at times between 6 and 9 min after burst.32 A direct observation of such foam was made by personnel who passed through @ patch that read in excess of 50 r/hr at 2 hr after Shot Umbrella. Never- theless, it was concluded® that combatant ships could safely traverse an Unbrella-type detonation area at about 25 min after burst, because the shielding provided by the ships structure and the height of decks above the water surface would result in sufficient attenuation of any gamma 17-103 ce pee ee ne ere ee