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.
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