A Monte Carlo study of the response of a germanium detector to electrons and positrons

Abstract

A Monte Carlo code has been developed which predicts electron and positron response functions of a planar intrinsic germanium (Ge) detector. The operational flow chart for the main program is given and the function of each subroutine is discussed. The characteristics of the response functions are studied by considering effects due to bremsstrahlung, annihilation radiation and the total electron transit distance. It is found that electron spectra are distorted primarily near the full energy peak by bremsstrahlung while positron spectra are seriously distorted by both annihilation radiation and bremsstrahlung. Total transit distances calculated here are found to be in good agreement with those calculated using the Bethe-Bloch formula. The effects of bremsstrahlung, annihilation radiation and total stopping distance, calculated independently in the complete code, are then used to construct an abbreviated version which reduces the computer time by a factor of 16. Sample computations are presented for a 16 mm diameter by 7 mm thick, planar detector. The calculated response functions reproduce experimental spectra accurately; they are also used to analyze positron spectra and obtain endpoint energies.