Modeling of the spectrometer for INTEGRAL satellite

A probabilistic approach has been presented for modeling the spectrometer for INTEGRAL satellite (SPI). We have considered the isotropic scattering of gamma-rays inside the detector, as well as the equal absorption probabilities of successive gamma scatterings inside the detector. Expressions are obtained for the addback factor and the peak-to-total ratio in terms of two parameters. Results have been compared with experimental data.