A STUDY OF AIRBORNE RADIOACTIVE SURVEYING

Airborne radioactivity surveys by the Geological Survey of Japan have already 1960] covered an area of about 90, 000 sq. km . On the basis of a semi-empirical theory on attenuation of gamma rays, with reference to the effect of scattering, the intensity distribution of gamma rays in the atmosphere was calculated by assuming several ideal forms of sources. 3 The fundamental constants in the theory are determined so as to conform to the relationship between the altitude and the experimental values of gamma ray intensity. From the results of calculations, the relationship between the altitude and the intensity of atmospheric gamma rays originating in a uniformly widespread source are discussed, and altitude correction is examined. It is concluded that the altitude correction is affected by the topographic variations, the existence of a thin surface layer, and by the variation of quantities of atmospheric radioactive materials. Anomalous gamma ray intensity, as observed in the airborne survey, and the determination of flight line intervals are briefly mentioned. Additional mention is made on the airborne survey over the rugged mountainous districts of Akita and Niigata prefectures, and on the test flight of a large size aircraft for the purpose of precise surveying. --Auth.