A Borehole Gamma-Ray Spectrometer For Uranium Exploration
This paper 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 correspondingto 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. Some overall specifications for the system are:Detector sizes -- 31 and 7. 2 cubic inchesGain stabilization source -- 54Mn (835 KeV)Typical count rates (large detector) --K window 8. 2 cps/percent KU window 0. 98 cps/ppm eUTh window 0. 22 cps/ppm eThPhotopeak resolution (835 KeV 54Mn) -- About 8 percentTypical logging speed -- 5 feet per minuteTypical count interval -- 10 secondsTypical data point density -- 1 data point per foot of boreholeData storage medium -- DC300A Cartridge Magnetic TapeStored and listed data -- Depth, measurement time, K-U-Th (per data point) counts, total counts, speed
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