In clouds fron detonations in of the total yield, the percent 100 factor proportional t+ the ratio of The accurlated radiation dose which the fission yield is less than radiation dose rate is reduced by a the fission yield to the total yield. that one receives in transit through (1) the radiation dose the cloud is a function of two primary factors: : rate in the cloud (related to time after detonation, to the ratio of the fission yield to the total yield, and to the portion of the cloud through which transit is made, i.e., stem or mshroom);and (2) the length of tim . spent within the cloud as determined by the speed of the aircraft and the horizontal dimension of the cloud at the altitude of penetration. The diameters of the stem and mushroom increase somewhat with creater vie lds. Considering all these factors, two generalizations, substantiated by the penetrations actually flow, may be made: (1) with the tropo- pause at 55,000 feet, ons zay fly through the cloud from any yield for a l00-percent-fission weapon in a high~performance aircraft at an alti- tude of 45,000 feet at 20 minutes after detonation for an expected ra~ diation dose of 25 r; (2) with the same height tropopause, one may fly through the cloud (stem) from any 100-parcent-fission weapon at 30,000 sa feat as early as 10 minutes after detonation for a radiation dose of the same magnitude. * Moderate to severe bumpy turbulence was encountered in one of the clouds penetrated at times of 22 to 40 minutes after detonation. Slight to no turbulence was encountered in the othsr clouds penetrated during a Similar time range, Turbulence was not a problem in any of these penetrations, and it was considered not likely to be a serious problem in a penetration as early as 10 minutes after detonation. Icing was encountered in soms of the penstrations, but caused no difficulty, except in the case of two aircraft penetrating a cloud from a water-surface detonation at the maximum altitude of 50,000 feet. This icing forced the pilots of these aircraft to reduce power on the jet . engines in order to avoid overheating. The contamination factor on the B-57B aircraft, as defined herein, averaged 0.6 & 0.2 percent per minute in penetrations of clouds from air, land-surface, and water-surface detonations, This factor enables one to estimate that portion of the total dose received which is accrued during the flight back to base after exit from the radioactive cloud. .In the penetrations made for this project, the return flight took about 50 minutes, and the come~home dose averaged about 15 percent of the total, On return flights of 2 to 3 hours duration in this aircraft the coms-homs dose would be no more than 25 percent of the total dose for early penetrations of the cloud. 4e2 . “* RECOMMENDATIONS There are no recommendations at this tim. BEST AVAILASLE COPY * “7