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 gammadose rate 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 oun the non-washdown ship, the YAG-40. The washdown effectiveness based on dose and dose-rate measurements in the interior of the ship decreased in the areas more remote from the deck. This fact indicates thar sources of radiation other than the washed-down deck become important at the morcremote locations. The data from the building-material panels placed aboard the ships after Shot 2, when corrected for an estimated difference in fallout of a factor of ten, indicated a wasndowua 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 4* (6.5) u ti x steel thickness tt Where: I = observed dose rate effective absorption coefficient (to be determined) Ip = source dose rate The average values of » 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 » can be utilized in a formula for the radiation from a plane~source dis- tribution to calculate the shielding factors. In more heavily shielded location (e.g., in the concrete-covered recorder room), the actual shielding is not as eftective as the cal- culated 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 ships, 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-detection system, 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 order of 0.6 me/m’. A similar detector placed on Parry Island detected peak levels of 0.15 and 0.003 82