the bag to capacity (15 cu ft at sampling altitude) in about 12 seconds at which time the expanded sides of the bag pressed against an electric switch closing the bag valve. On landing, the air in the bag was pumped through a particulate filter into a cylinder, leaving the radioactive contaminant adhering to the inside of the bag or to the filter material. It was determined that the R factors obtained were normal, and that the two decay slopes measured (-2.08 and -2.35) were relatively higher than decay slopes determined for samples obtained from other opera-~ tions and by other sampling methods. Activity levels of samples obtained in these tests were too low to provide more than limited data. The low readings were attributed both to the fact that aircraft speed was such that the plane flew well beyond the sampling zone by the time the bag was filled and to the ier, considerable decay occurring during the 45 hr required to ship the samples to the counting laboratory. The final report of this work appeared as CRLR-197, and WT-617. CRIR - 109 - RESULTS OF CHEMICAL CORPS CHEMICAL AND RADIOLOGICAL LABORATORIES PARTICIPATION IN OPERATION THUNDERCLOUD. (Part of JANGLE, wT-401) John R. Hendrickson and Robert L. Hanzel, 24 November 1952. SECRET-RESTRICTED DATA’ ” Three investigations are described in this report: (1) the shielding afforded by a medium tank and a personnel carrier against the radioactivity resulting from an aerial atomic blast, (2) the evaluation of filter efficiency of a tank collective protector, and (3) a determination c tion of the extent to which clothing is contaminated when worn by men marching within 500 yd of ground zero shortly after the blast. Film badges indicated 94% to 99% lower dosage inside the tank than outside, and similar readings inside the personnel carrier showed 95% shielding by this vehicle. Filter efficiency of the tank collective protector was found to be very high, with negligible radioactivity penetrating the type 6 filter material. No problem was presented by contamination of either impregneted or unimpregnated clothing worn near ground zero at H + 4 hr. Shoes showed the highest contamination, approximately 2 to 3 times background.