average value of 1.02 with a standard deviation of 0.11.
These comparisons showthat, with
few exceptions, there is good agreement and apparently no bias between results obtained from
GITR and ‘ilm-badge dose data.
3.2
REMOTE-SOURCE GAMMA RADIATION
The directionally shielded GITR Station 14 was designed to permit discrimination between
remote-source radiation and high backgrounds of radiation from aeposited contaminants.
How-
ever, examination of the data indicated that the background of radiation from contaminants on
the ‘washed weather decks was So low that the differences between remote-source and total radiation were smaller than the probable errors in the radiation measurements. This led to the
following approach for estimation of the remote-source-radiation contribution to the total radi-
ation observed on the washed weather decks.
The basis for the estimation technique was examination of the decay-corrected plots of the
average total dose rates on the weather decks, which are presented in Figures 3.37 through
3.40. Measured decay data were available for the period later than 6 minutes after Shot Umbrella (Section 3.4). For Shot Wahoo and for the period earlier than 6 minutes after Shot Umbrella, estimated probable limits for the unknown decay curve were based upon: (1) the calcu-
lations of gamma dose-rate decay for unfractionated fission products (Reference 10); and (2)
straight-line extrapolation on the log-log plot of the measured gamma dose-rate decay shown
in Figure 3.42.
The following discussion requires the assumptions that some undetermined
decay-corrected dose-rate curve can represent the buildup of contaminants on the ships’ weather
surfaces; and that this unknown curve always had either zero or positive slopes during the period
of interest, even though the decks were continuously washed (Reference 3 indicates that the major value of washdown is the continuous suppression of contaminant buildup). Consider the above
assumptions and refer to Figures 3.37 through 3.40.
The minima between the two major peaks
of the Shot Umbrella curves can certainly be considered to be upper limits of the decay-corrected
dose rate from fallout deposited on the weather surfaces of the ships at the indicated times, be-
cause even if no radiation was contributed by airborne radioactivity (which may not have been
the case) the contribution from deposited fallout could not be greater than the total, For similar
reasons, those portions of the curves which tend to level off after the last major peak for either
shot can also be considered upper limits of decay-corrected dose rates from deposited radioactivity, especially if there was a significant drop in the decay-corrected dose rate after the nearly
horizontal portion of the curve. Therefore, if the assumption of a continuously increasing buildup of contaminants is valid, it follows that overestimates of the contribution by deposited contaminants to the decay-corrected dose rates can be represented by the horizontal lines labeled
as such in Figures 3.37 through 3.40.
These decay-corrected estimates were converted to dose
rates that were integrated to obtain upper limits of the estimated dose contributed by deposited
contaminants for each assumed decay curve.
The estimated doses contributed by remote-source radiation to the total doses observed on
the washed weather decks of the three target ships, based upon the above-mentioned approach,
are presented in Table 3.10. These values indicate that at least 95 and 98 percent of the total
dose observed on the washed decks was due to remote-source radiation resulting from Shots
Umbrella and Wahoo, respectively. As a consequence, the observed total-radiation data can
adequately represent the remote-source radiation for the washed weather-deck areas during
the first 10 minutes after shot. Unfortunately, there was no data available from which it would
have been feasible to estimate the percent contribution of the remote-source radiation to the
total dose for unwashed weather decks.
3.3
TOTAL GAMMA RADIATION IN ADJACENT WATER
The attempt to measure the radiation in the water adjacent to the target shipS was not suc-~
cussful.
No data was obtained for Shot Wahoo, because the starting signals were not received
29