Monte Carlo simulation of a NaI[Tl] detector's response function

Abstract

Scintillator detector responses to gamma sources directly depend on the deposited energies of the gamma sources, enabling adequate detector calibration. Non-availability of gamma sources requires adoption of other means of parameterizing detector response functions within the energy range of interest. Computational means can be used to simulate series of random processes resulting in the deposition of gamma source energies and its conversion to voltage pulses. A Photon TRANsport (PTRAN) code was written to simulate a NaI(Tl) detector's responses to photon and electron interaction processes within the cylindrical crystal. The PTRAN general Monte Carlo code took into account photon transport in detector system with well-defined crystal geometry; and random processes within the detector system. The generated data were plotted to yield simulated pulse height spectra on exposing the scintillation detector to incident gamma sources within 0.2 to 2 MeV . The simulated full width at half maximum (FWHM) of the photopeaks of the sources resulted in detector energy resolution of 0.01% deviation from experiment for Cs-137 and 0.66% for the two lines of Co-60. The ratio of the peak-to-total area under the spectrum was simulated to be in good agreement with experimental value. The PTRAN code can be relied on in calculating the response functions when relevant and adequate number of gamma sources are not available. The code can also be modified to accommodate other detector crystals and different geometry types.