Gamma-ray detector properties for hostile environments

The environmental conditions of borehole logging result in detector properties that are continually varying, primarily because of the variation of material properties with temperature. The authors examine the important properties that vary with temperature, namely, the light output of scintillators (and, correspondingly, the noise of semiconductors), the decay time constants, and the emission spectra. The emission spectrum of a scintillating material is especially critical for matching to photocathode response spectra, because of the significant restrictions on photocathode materials that can be used in a nuclear logging tool. In addition, the severe restrictions on detector volume and the frequent presence of neutrons, in addition to gamma rays, in the region of the measurement provides additional constraints on the types of materials that can be used for detecting gamma rays.