Investigating the effect of depth of interaction on coincidence time resolution

The timing properties of scintillator-based detectors are a matter of importance in a wide range of fields. As fast scintillators progress and the sensors that preserve the quantized nature of the luminescent signal evolve, the optical transfer time may not always be negligible in ultra-fast time measurement. The present paper discusses the implications of this in a specific configuration for ultra-fast time measurement. To this end, we consider factors influencing the time spread such as the distribution of depth of interaction, non-instantaneous scintillation emission mechanism, and optical transport kinetics. Although such a topic has previously been studied by researchers, the aim of this work is focused on analyzing the detailed factors that govern arrival time spread. From these factors, we are able to obtain the post-interaction time spread, and we then derived the optical transfer time spread (OTTS) by a weighted sum of post-interaction time spread based on the cumulative density function of the depth of interaction. Based on the rejection sampling method, we could obtain the set of arrival times by the OTTS, and then the coincidence time resolution of radioactive sources was calculated. Consequently, we found that the difference in the attenuation coefficient causes the difference in the arrival time distribution, but it does not lend a significant contribution to the coincidence time resolution. In addition, when radiation with different energies is incident, the emission mechanism has a dominant effect on the time resolution, and thus incident radiation having higher energy in the same detector system has a higher light yield, which can exhibit better timing resolution compared to radiation with relatively low energy.