Light-transport incorporation to MCNP's PTRAC card for modelling sodium iodide scintillator response to gamma rays

The paper presents the detailed procedure for generating the response function of sodium iodide scintillation detector when exposed to mono-energetic gamma rays of Cs-137 source. The deposition energies of incident gamma rays within the scintillator are calculated using the PTRAC card of the multi-purpose Monte Carlo code, MCNPX, whilst the scintillation light transport simulation is undertaken with PHOTRACK code as a post-processing program. Finally, an extra broadening corresponding to the presence of multiplier tube (PMT) and the statistical fluctuations of scintillation light emission is utilized to produce a simulated response function that is comparable with experimental pulse-height distribution of the NaI(Tl) detector. The so-called wall (or edge) effect has been evaluated to incorporate the partial energy deposition of secondary electrons at the scintillator boundaries. Similar simulations can be performed to model the response of sodium iodide (and other inorganics) scintillator to the gamma-ray sources with an energy spectrum as well.