Dictionary:Gamma-ray log (GR)
A well log that records natural radioactivity. Also a generic term for any logging system based on gamma irradiation and measurement of resulting reactions. 1. In sediments, the log mainly reflects shale content because minerals containing radioactive isotopes (the most common of which is potassium) tend to concentrate in clays and shales. Volcanic ash, granite wash, some salt deposits, and some sedimentary uranium also give significant gamma-ray readings. The log often functions for correlation purposes, especially in cased holes. See Figures D-5, L-3, and N-2. 2. Used in exploration for radioactive minerals such as the uranium minerals. 3. See natural gamma-ray spectroscopy log and induced gamma-ray spectroscopy log.