Main operation characteristics of radiation detectors, using various scintillation substances, are calculated on the base of a realistic optical model of a scintillator. The calculation method takes account of a mirror-type maximum of the diffuse reflection indicatrix which is important for light collection in a scintillator. The comparison is carried out between various cases. Differing in the scintillator geometry, the type of reflecting surface, and the way of coupling the scintillator with the photoreceiver. Calculation results permit one to make a reasonable choice of scintillator sizes and reflector type for various specific applications. Some other possible applications of the calculation method are considered.