que Shielding factors against gamma radiation were found to range from 16 to 20 for M24 tanks, from 45 to 55 for M26 tanks, and from 10 +7 to 12 for T18El personnel carriers. The concentration of airborne activity in vehicles, extrapolated to H + 1 hour, averaged 0.25 me /1 and was not significantly affected by the hatches being open or closed. With soil conditions similar to those of the Nevada Test Site, satisfactory decontarinstion of vehicles was achieved by hosing the exteriors and vacuum cleaning the interiors. The efficiency of filter material in the tank collectiveprotectors was found to approach 99.98%. The running of vehicle engines while exposed to a base surge was found to result in nonhazardous contamineti: of air-cleaner and crankcase oil. CRLIR - 137 - SOME TECHNIQUES APPLICABLE TO THE STUDY OF ABD FALLOUT. (Operation BUSTER-JANGLE) \ Malcolm G. Gordon and Benjamin J. Intorre, October 1952. SECRET-RESTRICTED DATA Three methods are outlined for distinguishing, by autoradiograph: methods, between radioactive and nonradioactive particles from atomic blast fallout. Because these methods depend on particle size, reference is maie to the processes employed in separating fallout into various size ranges. Microscopic examination of the autoradiographs permits the counting of radioactive particles when a light background is used to accentuate the Garkened area surrounding every radioactive particle. When a dark back- ground is used, count may be made of nonradioactive particles. It was deterzined that a higher proportion of the larger sized particles is radio~ active than of the smaller particles. Of the particles in the 150y to 850 range, 17% are radioactive, while in the 8y to 38y range only 1% are radioactive. CRLIR - 158 - THE DEVELOPMENT OF A RADIOACTIVE SOURCE FOR A TRAINING AIT. James C. Kerrigan, 14 August 1952. UNCLASSIFIED (U) Commercially available radioactive source capsules do not possess field symmetry, with the result that instrument readings taken at points eguid-stant from the source are not uniform. Because an important use cf & standerd radioactive source is the calibration and checking of survey instruments in the field, the Radiological Division, C&RL, found it necess=sr to develop a training-aid source having fieid symmetry. RESTRAINTA ee '