Optimization of BaF 2 PAL-spectrometer geometry on basis of the Geant4 simulations

Abstract

Incorrect choice of measuring geometry and signal discrimination thresholds for the BaF2 PAL spectrometer can lead to a significant distortion in the measured spectrum of positron lifetime. The contribution of the distorted events for non-optimal geometry (e.g. "face to face") can exceed 50%. It reduces the lifetime of the spectral components and redistributes intensities. Geant4 simulation permits to evaluate influence of measuring geometry on spectrum distortion and to choose the most appropriate discrimination thresholds. Optimal geometry with a lead absorber between the detectors permits to reduce contribution of distorted coincidences to less than 1% and to provide sufficiently high count rate of true events.