A semi-empirical Monte Carlo based model of the Detector Optical Gain of Nuclear Imaging scintillators

Abstract

This paper reports a theoretical model of the optical gain of single-crystal scintillators of Nuclear Imaging. The model described the generation, propagation and escape of scintillation light as function of thickness and absorbed gamma ray energy. The latter was calculated via Monte Carlo methods at various crystal depths. The energies of 140 keV, 364 keV and 512 keV were investigated. The adopted thickness and energy values cover the range utilized in nuclear medicine imaging. For the semi-empirical approach, theoretical results were compared to experimental data for photon energies of 140 keV and 364 keV and the model's optical parameters were determined by the trial and error method. The results rendered the calculation of the optimum crystal thickness per investigated gamma ray energy. The presented results could be useful in designing nuclear medicine imaging systems.

Optical Photon Propagation Characteristics and Thickness Optimization of LaCl3:Ce and LaBr3:Ce Crystal Scintillators for Nuclear Medicine Imaging

“…The model also considers the X-ray attenuation properties in the crystal, the intrinsic conversion efficiency, showing the fraction of the absorbed X-ray or gamma-ray energy converted into optical photon energy [36], and the reflection of the optical photons at the input and output crystal surfaces. A more in-depth explanation of the model has been described in previous studies [33,35].…”

“…It is hypothesized that an equal number of optical photons, produced within the crystal's mass, are traveling in both forward and backward directions [33,35]. By considering all the reflections that occur between the entrance and the exit surfaces of the scintillator, we can determine the proportion of optical photons, produced in the nth layer, that manage to escape the crystal by the relation [35]:…”

“…The present study focuses on the determination of the optimal crystal thickness of the aforementioned crystals for Nuclear Medicine Imaging applications. For this purpose, a theoretical model [33][34][35][36] is applied for the estimation of the optical efficiency of the two single-crystal scintillators in terms of Detector Optical Gain (DOG), i.e., the number of emitted optical photons per incident X-or gamma-ray photons [33,35]. The model describes the light collection efficiency of a single crystal as a function of thickness and incident X-ray or gammaray energy.…”

Optical Characteristics of ZnCuInS/ZnS (Core/Shell) Nanocrystal Flexible Films Under X-Ray Excitation

“…The considered theoretical model has already been applied for scintillators with a crystal-like powder and structured form [32][33][34][35]. In this model, the transfer of the signal in the scintillator can be modeled by accounting for the transmission per layer.…”

“…Optical photons are generated and assumed to propagate either in a forward or backward direction. The optical photon flux is reduced either by internal optical photon absorption or by optical photon escape when the photons were incident on the surfaces of the crystal [32][33][34]. It has been assumed that per crystal layer only a fraction, hereafter called k, propagates Crystals 2019, 9,343 3 of 11 to the next layer.…”