Abstract: Improved radioactivity well logging by mounting a scintillator and photomultiplier tube in a single case interfacing with a hole extending through a drill collar at the lower end of a drill string so that measurements can be made while drilling. Radioactive sources (when required for well logging) are mounted in cavities which open to the exterior of the drill collar. Light from the scintillator is coupled directly to the aligned photomultiplier tube both of which are mounted in a case extending radially within the drill collar and sealingly engaging an electronics housing within the drill collar and the drill collar wall surrounding the hole. The scintillator is of greater diameter than the photomultiplier tube. A frustoconical light pipe connects the scintillator and the photomultiplier tube, channeling scintillation in the crystal to the photomultiplier to provide an amplified detection capability over that for a scintillator having the same diameter as the photomultiplier tube.

Abstract: Gamma spectrum measurement signals received from a downhole instrument containing a scintillation counter are coupled into a multi-channel analyzer. The analyzer converts the received pulses to pulses in separate channels according to energy levels of the received measurements. The energy channels from the multi-channel analyzer are coupled to digital decoders which are set up for energy level windows for preselected elements and the total occurrence count. These outputs are coupled into a microprocessor stripper which includes storage buffers sized in accordance with the logging rate and crystal utilized in the scintillation counter. These storage registers permit filtering in addition to stripping the various energy channels of the influence radiation caused by the elements having and energy band centered around a higher energy level.