abeam.
Installation of nozzles along the sides of the ship or maneuvering the ship would
have alleviated this difficulty.
The washdown effectiveness based upon the reduction of accumulated gamma dose
averaged approximately 90 percent. The effectiveness based on gammadoserate after
the cessation of fallout averaged approximately 94 percent. In general, this system was
found to be more effective than any subsequent decontamination effort performec on the
non-washdown ship, the YAG-40.
The washdown effectiveness based on dose and dose-rate measurementsia the interior
of the ship decreased in the areas more remote from the deck. This fact indicates that
sources of radiation other than the washed-down deck become important at the morrremote locations.
The data from the building-material panels placed aboard the ships after Shot 2, when
corrected for an estimated difference infallout of a factor of ten, indicated a wasndown
effectiveness of greater than 95 percent based on dose rate.
The effectiveness measured
on the aircraft was comparable to that measured on the ships’ decks.
The only material damage noted on the aircraft from exposure to salt-water washdown
was manifested as excessive magneto drop-off, some minor rusting of unpainted ferrous
metals, and the presence of excessive water where the lead goes into the spark plug.
6.2.3 Ship-Shielding Studies. The detectors placed within cylindrical steel shields
yielded data on the effective absorption coefficient as a function of time. The data can
be fitted with a function of the form:
I= ige HX
(6.5)
Where: I = observed dose rate
x = steel thickness
p = effective absorption coefficient (to be determined)
Ip = source dose rate
|
The average values of u are plotted in Figure 6.3 versus the time since the detonation.
Observations below decks indicate that for relatively lightly shielded locations, the measured. values of 4 can be utilized in a formula for the radiation from a plane-source distribution to calculate the shielding factors. In more heavily shielded location (e.g., in
the concrete~-covered recorder room), the actual shielding is not as effective as the calculated shielding, presumably because the sources of radiation other than the contaminated
decks become important. The measured shielding factors on the YAG-40 were between
0.1 and 0 2 between the second and upper deck, and between 0.03 and 0.05 in the hold.
The corresponding YAG-39 values were 50 to 100 percent larger than these. In the
superstructures compartments on both sbips, the shielding factors ranged from 0.1 to 0.6.
6.2.4 Airborne-Activity Studies.
Airborne activities were measured above decks and
in ventilation and boiler air ducts during fallout, and above decks during decontamination
operations.
These measurements provided data on a fallout-detectionsystem, inhalation
hazard to crews above and below decks, activity-removal efficiency of various ventilation
systems, and inhalation hazard to decontamination crews.
Peak airborne beta activities aboard ship were measured to be of the orderof 0.6
mc/m'. A similar detector placed on Parry Island detected peak levels of 0.15 and 0.003
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