ae cS cea n nae ‘y tantalum pellets were used. The work deals with the ultimate size of particles resulting from disintegration of the test pellets and with the extent to which such hazardous particles might become airborne with varying wind velocity. o The humidity at which tantalum pellets are disintegrated has no effect on the particle size, although it does affect the rate of disintegration, higher humidities producing more rapid disintegration. Particle-size distributions and quantities of airborne tantalum were determined in wind-tunnel tests. At a wind speed of 10 mi/hr, 7% of the tantalum became airborne, and 99% of this airborme material was found to be 1l3u, or smaller, in size. In small-scale field tests, contamination of a desert area with the test agent resulted in no detectable airborne radioactive material at wind velocities up to 20 mi/br. With wind velocities of 25 mi/br and simultaneous distwrbance of the area by vehicular movement, radioactivity was noted 200 ft downwind of the area to the extent of only 5 x 10710,¢/cc. CRLR - 188 - RADIOACTIVE PARTICLE STUDIES INSIDE AIRCRAFT (UKP-8). (Operation UPSHOT-KNOTHOLE) John M. Roady and Nicholas 5. Capasso, 11 June 1953. CONFIDENTIAL Samples were taken of air entering the cockpits of F-80 drone aircraft that penetrated the atomic clouds a short time after the detonation of two of the airburst shots of Operation UPSHOT-KNOTHOLE. Particulate matter in the sampled air was collected on the slides of a five-stage cascade impactor and on a millipore filter attached to the effluent end of the impactor. This report records the test setup employed for evaluation of the potential inhalation hazard to which aircraft crews would be subject on passing through an atomic-bomb cloud. For such evaluation it was necessary to collect4& suitable sample of the cloud particulate matter of the size range in which lung retention is a maximum (0.ly to 10, diam). The collection was made ina manner that made possible the determination of: (1) concentration of alpha and beta activity in the air; (2) particle-size distribution and activity vs particle size, (3) specific activity of individual particles in the specific size range, (4) total activity of air in the cockpit at peak concentration, and (5) the rate of dilution of this air by clean air upon emergence from the cloud. measurements were made. The samples were later analyzed, and supporting The final report of this work appeared as CRIR-299 and WI-71T. eee. 28