CHAPTER 17 consisted of solid particles, with an insignificant number of slurry particles revealed by microscopic examination. The fallout analysis of Ref.42 was not of close-in fallout, since the samples used were collected on the support ships, which were 20 miles or more from surface zero. Shipboard fallout measurements were made at Operation Redwing 41, 61 during maneuvers (similar to those at Operation Castle) of the YACs through the predicted fallout areas. Since the shipe were manned, lowactivity areas were traversed, and instead of one ship with washdowmn and one without, each ship was equipped with a partial washdown system. Therefore, more accurate appraisals could be made of washdowmeffectiveness than was possible at Operation Castle where the two ships were, of necessity, some distance apart and hence experienced somewhat different fallout conditions. During the Shot Flathead operation,?! the YAG 40, at 40 mtles north of surface zero, intercepted slurry-type fallout et H + 8.2 hr, and remained in fallout until H + 23.7 hr. As the ship maneuvered, a peak value (in time) of the average (over the deck) dose rate of 0.011 r/hr was re- corded at H + 17 hours on the washed area of the main deck, while a “peak mean” dose rate of 0.266 r/hr was recorded on the unwashed area of the main deck. A similar washdown effectiveness is demonstrated by the mean total accumilsted dose of 0.126 r recorded by 23.7 hours on the washed area, while 3.04 r was recorded in the unwashed area. Thus, results observed at Operation Castle were confirmed, since the average dose and dose rate in the washed area were less than 10% of that in the unwashed area. It should be noted that the average dose in the un- washed erea*! had increased to about 6 r at 48 hr, when the ship returned to base.*! During the Shot Navajo operation,®! the YAG 39, at 22 miles north of eurface zero, intercepted fallout of salt-water slurry at H + 2.4 hours, and remained in the fallout area till long after fallout cessation, which occurred at about H + 13.4 hr. A peak mean dose rate of 0.177 r/hr was recorded on the washed area of the main deck at H + 6 hr, a value significantly lower than the unwashed-area peak mean dose rate of 1.4 r/nr. The accumilated mean gamma deck doses recorded at the end of washdown (at 9.4 hr) were 0.721 r and 5.48 r in the washed and unwashed areas, respectively, whereas at the end of fallout (at 13.4 hr), mean total doses of about 1.0 r and 7.5 r were recorded in the washed and un- washed areas respectively. Apparently, waghdown was not as effective in removing the fallout from this shot ae it was in the other cases, probably because the system was operated intermittently, since it was necessary for personnel to be on deck at several times during the maneuvers. The average dose on the unwashed area increased to about 10 Yr, recorded by about 43 nr. 4! PY BEST AVAILACLE CO 17-73