products from the explosion, condensed oxides of the components of a nuclear device and associated equipment, and air, It also contained atmospheric dust from the air entrained during its rise, It could also contain dirt from the explosion site and condensed moisture, The latter components caused the primary cloud to appear white in reflected light but in such cases the interior was found to be suffused with typically reddish brown light. . The primary cloud was identified not only by its color but also by | the presence of gamma radiation near or within it. Except for the radiation field in the free air outside the cloud and where material was too diffuse to be seen clearly, it was found nearly always that the color and radiation field occurred together, Many photographs of stabilized clouds from nuclear explosions clearly showed the reddish brown color of the primary bomb material lying uppermost, especially for the relatively low air burst. Below the main upper cloud, the color faded into the gray dust from the explosion site raised by the shock wave and vertical air currents in the explosion and cloud rise. For very high burst heights relative to yield the lower cloud material was unmixed with the dirt from the explosion site, In case of very low bursts considerable amount of primary bomb material might lay below the primary cloud but its color was masked by a high concentration ofdirt, Because, in any case, this lower material could not be representative of the total explosion debris, sampling was usually conducted at altitudes within the main upper mass, 202 SWEH~2 -003) e io ¢ AFWifHO \ Talat