Contribution of pair production process in full-energy peak efficiency calculation of semiconductor detectors for axial point sources with high-energy γ-rays

Study has been made of the contribution of the pair production process in calculation of detector efficiency. Particular attention has been paid to positron annihilation in flight and subsequent scattering of the annihilation quanta in the detector material. A mathematical formula has been derived to directly calculate the liner attenuation coefficient of the full-energy peak (μp) for a Ge (Li) detector using an axial point source. The calculated values of the photopeak efficiency are found to be in a good agreement with published experimental data.