A novel asymmetrical peak broadening feature for a CdZnTe detector response function modeling using PHITS particle and heavy ion transport simulation code

In this paper we present the results of a detector response function modeling using a new version of PHITS Particle and Heavy Ion Transport Code with an advanced feature for asymmetrical peak broadening. Tests are performed on a room temperature medium resolution 500 mm3 CdZnTe detector of a quasi-hemispherical design with validation on a set of point source gamma-ray spectra with a range of energies from 59 keV up to 1332 keV. Performance assessment is conducted with respect to built-in spectra broadening capabilities using as default Gaussian as well as an asymmetrical peak shape models. Results of our study indicate that up to 200 keV energy range where peak asymmetry is not severe a default Gaussian peak shape broadening can be used. Beyond 200 keV the degree of CZT photopeak asymmetry becomes significant and requires an asymmetrical peak shape broadening. This asymmetry affects the low-energy side of the photopeaks and has a non-linear behavior with energy. We find that with a built-in feature of a tailed peak shape model introduced in the new version of PHITS code (ver. 3.10) asymmetrical peak shapes of CZT detectors can be approximated. The analysis routines and mathematical formalism are described in detail and results are presented.