DNA 2240H~2 15% of the average unwashed weather-deck dose, for both Shots Flathead and Navajo, and was 15 to 17% of the weather-deck doses recorded at Shots Zuni and Tewa. Zuni was ea land-surface shot, and Tewa was de- tonated on the edge of a reef, involving a little water. ‘The average unwashed-deck dose up to 30 hr on the YAG*39 varied widely in magnitude for the four shots (0.4 r at Zuni, 2 r at Flathead, 9.5 r at Navajo, and 190 r at Tewe). On the YAG-40, where the unwashed-deck doses to 30 hr also varied greatly (65 r at Zuni, 4 r at Flathead, 1.5 r at Navajo and 85 r at Tewa), the doses in the upper No. 2 hold were between 7% and 12% of the unwashed-deck doses.?) The shielding factors quoted in the preceding peragraph probably closely approximate ship shielding against activity deposited on the @eck surfaces, although they were calculated on the basis of average total deck doses. The basis for the preceding statement is derived from data in Refs.41 and 61. It is estimated from data obtained for Shot Tewa that about 95% of the average accumilated dose to 30 hr on the unwashed deck of the YAG-39 was due to deposited activity, and about the same proportion held for the YAG@40 deck dose for Shot Zuni. Thus, for those two shots, it is estimated that in the upper No. 2 hold, the ships‘ structures shielded out about 85% of the radiation from activity de- posited on the weather-deck surfaces. Although the airborne-and deposit- radiation proportions of the total deck doses recorded for Flathead and Navajo were not estimated, it seems reasonable to postulate that the ships’ structures were as effective in attenuating radiation from activity deposited by barge shots as they were in attenuating radiations from the more nearly solid particulate material deposited by land-surface shote. Since the effect of the ships' structures on the total doses was about the same (for the same locations) for all four shots, it is postulated that in the upper No. 2 hold, the ships' structures shielded out about 85% of the deposited-activity radiations from the barge shots, as well as from the land-surface shots. 2. Underwater Bursts Operation Crossroads,Shot Baker: Shot Baker are of dubious value. Below-decks dose records from The exact placement of film badges with- in compartments was not specified, and not only was there “wide variation of doses received by badges subjected to approximately the same radiation,” but also “four of the sixteen unshielded badges (on 13 different ships) registered less dosage than some badges located inside the structure on the same vessel."“? on averaged data. Shielding-factor estimates have been made, based Although no distinction is apparent between shielding factors for amidships and for bow and stern compartments, the values vary with the thickness of steel, and lie between values of about 0.25 and 0.025.9° However, the proportion of the total below-decks dose due to activity deposited on t ecks is a matter of tornjecture, since it was estimated that only about 50% of the total deck dose was due to deposited activity. a BEST AVAILAGZLE COPY | 17-76