CHAPTER 17 17.8.3 Weapons-Test Data Ll. Water-Surface Bursts ration Castle: Measurements were made © in the ventilation systems of the test ships (YAGS 39 and 40) to obtain evidence on (1) the concentration of airborne activity entering them, (2) the effec- tiveness of ventilation countermeasures , and (3) the extent to which airborne material was deposited in the system. Small ventilation cubicles (16x 25x10 ft) were built into the between-deck space of the No. 3 hold of each YAG. Each cubicle had its own duct system with a mushroom-head type of intake, and the system was bullt to provide adequate flow for measurements of activity per unit volume of air carried into the spaces for seven different conditions of ventilation. The conditions included the standard system, operation of the fan at low speed, use of a precipitron mounted in the duct near the intake, use of an openmesh (ACC) filter, etc. Shots 2, 4, and 5. Some data were obtained following Attempts to accurately measure particle sizes of the radioactive material in below-decks spaces failed because of the low activity in the molecular filters at the time the analysis began, but it was estimated that the mean diameter of particles gaining entrance to the is ship's interior was of the order of ly or less. Measurements in the ventilation systems for Shots 4 and 5 resulted in the following conclusions: (1) there was a gradual decrease in con- centration of airborne activity between station 1, directly beneath the mshroom intake, and station 5, in the cubicle exhaust; (2) in the test systems where no particle-removing device was present, there was a marked uniformity of airborne-activity concentration, (3) in cubicles ventilated by unprotected duct systems, the average airborne-activity concentration was about 0.02% of the average weathereide concentration, and the particle concentration in the duct was not greatly influenced by the flow rate through the duct; (4) ventilation countermeasures (the ACC filter and the precipitron) effected a reduction of 94% to 98% in the airborne concentration; (5) gamma radiation from the ducts was about the same, or less than, the gamma radiation penetrating the decks fron weather-surface deposits; (6) an increase in activity occurred near the region of the supply-duct Y branches. Measurements in the boiler systems were obtained only from Shot 4, and indicated that asirborne-activity concentrations in the fire room of the YAG-O were negligible. Samplers located in the boiler systems showed higher deposition than those in the duct sections. However, significant comparisons could not be made between activity concentrations in boiler-air systems and either the weatherside area or the ventilation area. 17~107