Disclosed is an apparatus configured to detect radiation at high temperatures in a borehole penetrating the earth. The apparatus includes a scintillation material that interacts with the radiation to generate photons, at least one solid-state photodetector optically coupled to the scintillation material and configured to detect the radiation by detecting the generated photons, and at least one optical element disposed between the scintillation material and the at least one solid-state photodetector and configured to concentrate the photons generated in the scintillation material onto the at least one solid-state photodetector.