after burst received considerable theoretical study, the results were of little use for evaluating the radiation risk to piloted aircraft or the flight time within the cloud necessary to collect adequate samples at relatively late times after burst. Scientific personnel measured the radiation within bomb clouds and reduced the data to equations. Such equations included intensity in roentgens per hour and this time in hours after burst and the numerical constant was the intensity observed one hour after burst, This curve represented the decrease with time after burst in "peak intensity" within the cloud, Such peak intensities are found in the most persistent layers of the main cloud at altitudes where isokinetic streamline airflow exists, In the absence of cloud dispersion similar equations expressed the decrease of the ganma radiation with time after one hour after burst as a result of the radioactive decay of the source material. The first type equation served for operation planning purposes with the intensities within the cloud assumed to be independent of yield and altitude so long as sampling of the main cloud only was considered, A general rule which personnel applied to lower level sampling was that radioactive material and hence radiation intensity in the stem decreased in concentration tenfold for every 10,000 feet below the base of the main -8 cloud when burst conditions were constant, Estimation of the In-Cloud Radiation Exposure Required Within time limits defined by the radioactive intensity in a cloud the radiation exposure received by a sampling aircrew was controlled to 206 SWEH-2~003); / n9 p APHL/HO pt ge Ge.