This disclosure is related to the field of neutron well logging measurements for determining petrophysical properties of subsurface formations traversed by a wellbore. More specifically, the disclosure relates to methods and apparatus for determining whether signals generated by a radiation detector in a well logging instrument were induced by neutrons or gamma rays. The disclosure also relates to methods and apparatus for gain stabilization of radiation detectors.
Well logging instruments known in the art include various types of radiation detectors that are capable of detecting neutrons and gamma rays. Radiation detectors include gas-filled tubes in which the gas becomes ionized following a radiation event in the tube that the detector is configured to detect. Other types of radiation detectors include scintillation detectors, which may comprise a radiation sensitive scintillation crystal optically coupled to a photomultiplier tube. Scintillation detectors may be used, for example and without limitation, detecting gamma rays so as to be able to characterize the energy of the detected gamma rays by measuring the amplitude of each signal pulse generated by the photomultiplier tube.
There remains a need for a radiation detector, or a method or system utilizing a radiation detector, that delivers improved well logging performance.