Improvement of Time Resolution of BaF2 Scintillator for Low-Energy Gamma Rays by Digital Pulse-Shape Method

Abstract

A digital pulse-shape method (DPSM) is proposed to improve the time resolution of a BaF2 scintillation detector for low-energy gamma rays. By using chi-square fitting of digitally measured pulse shapes with calculated shapes, the proposed DPSM determined the pulse height and the start time corresponding to the deposited energy and the interaction moment, respectively, of gamma rays incident on the BaF2 scintillator. We calculated theoretical pulse shapes by considering light output, light-attenuation length, and light path within the scintillator. In particular, we calculated the light path inside the scintillator by using a Monte Carlo method. We performed coincidence measurements for gamma rays emitted from Na-22 and Ba-133 standard sources with two cylindrical BaF2 scintillation detectors and then we obtained a time resolution of around 6 ns for 81-keV and 511-keV gamma rays by using the DPSM. Although time resolution obtained using the DPSM was inferior to that obtained using a conventional analog signal process, it had a consistent value irrespective of gamma-ray energy.