Nonproportionality of Scintillator Detectors. IV. Resolution Contribution from Delta-Rays

This paper is the fourth in a series of articles published on the light yield nonproportionality of scintillators and its impact on the detector´s energy resolution. Herein, we focus on modeling the resolution degradation induced by delta-rays. To do this, we begin with Møller´s classic equation to describe collisions between incident high-energy electrons and those in the scintillator medium, which lead to the delta-rays. The trajectories of delta-rays having energies above a specified cut-off value are further analyzed to determine the resolution degradation induced by fluctuations in their light yield and ionization density. Our conclusion is that the delta-ray contribution to resolution is typically smaller but comparable to that arising from the primary electron. We have considered the cases for two illustrative scintillators: NaI(Tl) and LSO(Ce).