Effect of Surface Roughness and Crystal Shape on Performance of Bismuth Germanate Scintillators

To improve the scintillation output of bismuth germanate scintillators, the influence of surface roughness and crystal shape has been experimentally studied. We found that an optimum scintillation output is obtained for an appropriate aspect ratio of the scintillator, i.e., its length “h” to width “a” (h/a), depending on their surface roughness. A high scintillation light output can be obtained for polished scintillator surfaces when h/a>6, but for rough surfaces when h/a<6. In addition, when scintillator surfaces are provided with a reflective coating, the light output is markedly improved. The dependence of the light output on the surface roughness and crystal shape is discussed in terms of the transmission loss inside the scintillator and the reflection loss at the surface.