A Borehole Gamma-Ray Spectrometer For Uranium Exploration

This report describes a system designed to measure the concentrations of potassium, uranium, and thorium in boreholes. The system is divided into a linear pulse processing subsystem that consists of the probe and part of the surface electronics, and a digital recording subsystem. Gamma rays are detected in one of two NaI (Tl) crystals and the voltage pulses resulting from the scintillations in the crystal are linearly transmitted to the surface. The pulses are separated and counted in each of three channels corresponding to a window of energies in the gamma-ray spectrum. The resulting counts are then recorded on magnetic tape and optionally listed on a printer and strip-chart recorder. The recorded data are processed at a central computer where a graphic display of potassium, uranium, and thorium concentrations is constructed. Following a detailed description of the spectrometer system, some geologic/lithologic relationships are suggested where this system can be applied; some examples of log data obtained with this system are also included. 22 figures, 6 tables.