Different geometries of scintillation spectrometers are disclosed which provide improved resolution over prior art scintillation spectrometers. By ensuring that photons generated by scintillation events occurring in different locations within the scintillation material generate similar light profiles on the photo-detector, the output signal is made less sensitive to the initial interaction site. This can be achieved in a number of ways, such as: by limiting the exit window of the scintillation crystal to a smaller detector, by introducing an optical spacer (94) between the scintillation crystal and detector (99), and/or by making the crystal longer than necessary to stop the gamma rays. A principal advantage of these new geometries is that deconvolution of the raw-data is more effective, thus improving resolution.