CHAPTER 17 locations at Shots Umbrelle and Wahoo, respectively. The preceding statement is based on the estimate23 that at least 95% and 98% of the total dose on the washed decks of the destroyers was due to traneit radiation from Shots Umbrella and Wahoo, respectively, and the contribution of all other radiation to the total dose at below-decks locations was of little significance. At Shot Umbrella, doses of more than 200 r were recorded in many compartments of the two closest ships (at 1900 and 3000 ft from surface zero). The ratios of doses in compartments to those on washed weather decks ranged from 0.1 to 0.7 for non-machinery spaces and from 0.02 to 0.2 for machinery Tie ratios of peak dose rates showed similar variation. At doses of more than 500 r were recorded in most compartments closest ship (at 2900 ft) and doses of more than 200 r were aboard the next closest ship (at 4900 ft). spaces. 3 Shot Wahoo, aboard the recorded Existing data indicate that, at least under certain conditions, the transit radiation may contribute the major portion of the nuclear radiation aboard ship. These conditions occur when (1) yields, water depths, and burst depths are such that a contaminated base surge forms; and (2) when the radioactive particulate material formed is of such a nature that the washdown system is highly effective in preventing shipboard contamination. Since available data are insufficient for reliable scaling and extrapolating transit-radiation effects for any yield or burst condition (depth of burst and depth of water) it is obvious that methods for theoretical calculations of such exposures are required. Operation Wigwam: During the period when transit radiation was being recorded on the deck of the YAG-39, from 13 to 20 min after burst, there was no record of deposit dose. The peak dose rates of 300, 150, ana 18 r/hr recorded?! during this interval at the wheelhouse, internal, and deep-hold stations, respectively, therefore may be assumed to have been due to transit radiation. These interior peak dose rates thus were found to be 50%, 25% and 3% respectively, of the recorded exterior peak dose rate of 600 r/hr. 17.5.4 Theoretical Calculations of Transit Radiation for Unshielded Locations GENERAL No theoretical models for estimating transit radiation from water- surface bursts have been developed, but two models are available for subsurface bursts. Order-of-magnitude estimates for surface bursts are given in Ref. 47, which states "the fireball formed by a surface shot will vaporize water below it; this water, the explosion products, and entrained air will form a radioactive mushroom cloud. Below the cloud a tenuous stem or column of water will be raised and the coluwm collapse will probably create a relatively minor base surge ..... 17-39 en cence ee ee