Optimization of BaF2 positron-lifetime spectrometer geometry based on the Geant4 simulations

Incorrect choice of measuring experimental geometry and energy windows for a positron-lifetime spectrometer with BaF2 scintillators can lead to a significant distortion in a measured spectrum. Contribution of the distorted events for a non-optimal geometry may exceed 50%. It reduces the measured lifetimes of the spectral components and redistributes their intensities. The Geant4 simulation allows to estimate an influence of the measuring geometry on the spectrum distortion and to choose the most appropriate energy windows. The optimal geometry with a lead absorber between detectors suppresses contribution of the distorted coincidences down to 1% providing sufficiently high count rate of true events.