A gamma-ray spectrometer calibration system comprises a light guide, a photomultiplier tube, a laser, and analysis electronics. The light guide is optically coupled to the scintillation crystal, the laser and the photomultiplier tube, such that the laser can provide reference signals to the photomultiplier tube. In some embodiments, one or more temperature sensors are provided, such that the analysis electronics determine initial settings and adjust the initial settings based on the temperatures measured by the temperature sensors. Additional apparatus, methods, and systems are disclosed.