Ray tracing simulations in scintillators: A comparison between SLitrani and Geant4

The extensive use of scintillating crystals in medical imaging field is generating a growing interest in Monte Carlo simulation of light transportation and photon collection inside inorganic materials. The critical parameters under study which affect the performance of medical devices are the number of photons collected per unit of energy deposited (light yield), the energy resolution, the effect of dimensions and surface state and the time profiles of the scintillation process. Moreover, most of the crystals used in Positron Emission Tomography (PET) applications, such as lutetium orthosilicate (LSO), are anisotropic, potentially influencing the performances. In particular the recent development of time of flight PET scanners requires a detailed knowledge of timing profiles of the crystals in terms of time of arrival of single photons, scintillation rise and decay times. Furthermore the effort towards innovative endoscopic probe for PET examination requires an extensive analysis of the effect of the dimensions of small crystals on the parameters mentioned. Different simulation tools are employed nowadays for detailed studies of interaction of particles in inorganic materials and tracing of the scintillating photons produced. In particular our attention is focused on SLitrani and Geant4. SLitrani is a general purpose Monte-Carlo program simulating light propagation, developed for high energy experiments, in particular in the frame of the CMS experiment at LHC. Its most advanced characteristics is the ability to handle anisotropic materials, thus retaining a quite general application. Geant4 is a general purpose Monte Carlo toolkit widely used in high energy physics, astroparticle physics and nuclear physics, which includes an optical physics process category to simulate the production and propagation of light. In the frame of the Crystal Clear Collaboration, we have been developing and testing innovative scintillation technologies for medical applications, and with this respect Monte Carlo techniques are powerful tools for investigating the performances of our setups. In order to validate and accurately describe the inorganic crystals developed we have been comparing the performances of the SLitrani and Geant4 frameworks, and started a preliminary comparison with experimental results obtained in our laboratories.