Improving energy resolution of scintillation detectors

Scintillation detectors are widely used in gamma-ray spectroscopy, but their relatively poor energy resolution sometimes limits the effectiveness of the applications. Energy resolution of scintillation detectors used in gamma-ray spectroscopy is often dictated by the number of cathode electrons in the associated photo-multiplier tube (PMT). This is particularly true for lower light yield, high refractive index scintillator materials. This paper analyzes the operation of a bismuth germinate (BGO) detector and supports the above point with experimental data. We propose to enclose the scintillator inside the PMT vacuum chamber and to deposit photo cathode directly onto the scintillator surface. By removing the optically unmatched interfaces, total light collection and therefore cathode electrons will increase significantly. BGO energy resolution is projected to improve from the current best value of 10% at 0.662 MeV to about 6% (FWHM). As a side benefit, time resolution will also improve, as the signal rising ledge becomes less noisy.