A scintillation spectrometer provides improved resolution by ensuring that photons generated by scintillation events occurring in different locations within the scintillation material generate similar light profiles on the photo-detector, thereby making the output signal less sensitive to the initial interaction site and enabling more effective de-convolution of raw data. This is achieved in different ways, such as by: limiting the exit window of the scintillation crystal, introducing a spacer between the scintillation crystal and the detector window, or providing a crystal that is longer than necessary to stop gamma rays.