Calibration of an airborne gamma ray spectrometer over Mary Kathleen Uranium mine

Abstract

Airborne gamma ray spectrometer test flights were made over the Mary Kathleen Uranium Ltd orebody with a large crystal assembly and modern digital recording system. The decrease in response with height is shown theoretically to be a combination of an exponential air absorption factor and a geometrical factor. The results of these tests indicate that for this specific detecting system and gamma ray source, the overall attenuation effect with height becomes exponential for the total count and thorium channels with apparent attenuation coefficients of 7.4 ´ 10?3 and 7.6 ´ 10?3 m?1 , respectively. The uranium channel count rate shows a departure from an exponential relationship; this departure can be allowed for by a height dependent component in the stripping (Compton scatter) correction factor. Ground surveys with a calibrated portable spectrometer enable abundance conversion factors to be derived for the airborne system.