US Patent 10473802 Downhole energy calibration of gamma ray detectors

Estimating a parameter of interest, comprising intermittently generating a calibration radiation source in the carrier, the calibration radiation source comprising a radioisotope producing radiation to which the radiation sensor is exposed. Methods include measuring a calibration response from the radiation sensor with measurement circuitry during the exposure to produce calibration information, and measuring another response from the radiation sensor with the measurement circuitry to produce measurement information after the radioisotope has decayed to a reduced radiation level such that the measurement information is substantially unaffected by the radioisotope. The radioisotope may be a positron emitter producing radiation by annihilation of the positrons emitted from the radioisotope. The radiation produced may thus be gamma rays.