Observations on the accuracy of gamma spectrometry in uranium prospecting

The increasing requirement for more sensitive detection of buried uranium ore bodies emphasizes the need for more accurate instrumentation and for a better understanding of the physical principles of the techniques now in use. The paper considers some of the problems inherent in the use of in-situ γ-spectrometry which is believed to be a potentially powerful tool now available to the exploration geologist. It is shown that calibration factors based on a smooth (semi-infinite plane) calibration pad can be in significant error and it is now suggested how calibration factors more appropriate to the variety of situations encountered in the field might be applied to improve the accuracy of the data which is derived. The results presented are based on a series of simple experiments using small samples of uranium and thorium in a granular fluid bed, and applying the resultant data to a computational model from which the appropriate correction factors have been derived. The paper provides further information for the field geologist to acquire a fuller understanding and appreciation of the problems underlying the accurate use of in-situ γ-spectrometry. (author)