Design of high reliability nuclear logging probe

Nuclear Logging Probe may measure the naturally occurring gamma ray radiation level and detect gamma rays from a radioactive source within a well bore. It is used for depth correlation, lithology, mixture density measurement, identification of radioactive scale. But because of the harsh working environment, high temperature above 100 °C, high pressure, shock, it is difficult to get accurate measurement result. In this paper several possible cases that affect the measurement result were discussed; and then provide appropriate solutions. The application of photomultiplier tube (PMT), NaI crystal, design of photon counting unit, divider of PMT were also discussed; A detailed circuit with high reliability is presented. Some measured results of the actual circuit are shown.