any biologically accepted value, The ability to control this exposure, to predict the other flight variables, and to choose appropriate times for cloud penetration formed the basis by which sampling collection was conducted within an economy of radiation exposure, This economy was made quantitative through a relationship which expressed the amount of debris collected as a function of radiation exposure received and the other flight variables, On a single penetration of a cloud from a nuclear explosion a sampling aircraft collected a total quantity of fission products and "unburned® debris determined by the total effective filtering rate-of the filter devices which it carried, the volumetric concentration of fission products — in the cloud, and the time of flight through the cloud, The crew of the aircraft received an exposure determined by the radiation intensity within the cloud (excepting radiation shielding structures in the aircraft) and the time of the flight through the cloud, The total effective volumetric filtering rate was proportional to the number of filter devices carried, the true airspeed of the aircraft, the area of the filter paper carried in each filter device, and the efficiency with which the filter paper retained the particulate matter, If the mass of concentration: of inert material fromthe detmation was low the radiation intensity in the cloud was to a good approximation, proportional to the volume concentration of fission products, to the amount of radioactive decay which took place since the explosion, and inversely proportional to the air density at the altitude ' of penetration, Assuming that the radiation exposure received by the crew 207 AFWL/HO . SWEH-2-003) no oF