mc/m! at 12 hours after Shots 2 and 3, respectively. The instrument used was sensitive to 107° mc/m? if the background gammafield was less than 0.5 r/hr. Weatherside filter samples counted at 10 daya after the shot yielded values of about 2 x 10° counts/min/ft* of air drawn through them. This value represents an average over the time from the start of fallout till shutdown of the filters approximately 19 hours after detonation. The standard ventilating system operating at 1,000 ft?/min resulted in an activity concentration in the cubicle which was a factor of 1 x 10‘ to 2 x 10™ lower than that above Time , Hours ia® ar ve 08 ae ae B Steet , inches” 13 3 Le Figure 6.3 Apparent absorption coefficient » as a function of time. decks. Changing the flow rate had no appreciable effect, but the Naval Research Laboratory (NRL) preciprotron or Army Chemical Center (ACC) paper filters were approximately 95~percent effective in further reducing the activity. During recovery and decontamination operations, the airborne activity concentration was almost always less than 0.1 mc/m?. Respirators were worn by personne! operating a Tennant resurfacing machine principally for protection from flying chips. 6.2.5 Radiation Surveys. The radiation condition aboard an unmanned ship wasfirst estimated from data telemetered from a fixed gamma-detector station. A second order- of-magnitude estimate was derived by multiplying a reading made from aboard the re- covery tug hv a calculated factor. For purpose of scientific experiments and personneldosage prediction, more-accurate surveys were utilized. The ships were marked at approximately 900 points on the interior and exterior. The surveys were performed at these locations by groups of previously inexperienced Navy enlisted men. Surveys included readings of gamma dose rate at 3 feet, beta surface readings, directional gamma- 83