A detector and associated method are provided including a first scintillation material having a light yield temperature dependence and an output at a first energy level, a second scintillation material having a light yield temperature dependence similar to the first material and an output at a second energy level, and detection circuitry. The first and second outputs are responsive to radiation emitted from an ionizing radiation source. The detection circuitry includes a photo multiplier tube configured to convert photon outputs from the first and second scintillating materials to electrical pulses, a counter circuit configured to count the electrical pulses generated in the photo multiplier tube by the first and second materials, and a gain control circuit configured to monitor the electrical pulses generated in the photomultiplier tube by the second material and adjust a gain of the detector upon detecting a drift in the output of the second material.