PHITS code Monte Carlo simulation of a gamma chamber 5000

Gamma Chamber 5000 (GC-5000) is a dry storage irradiator manufactured by the Board of Radiation and Isotope Technology, India. The GC-5000 can be employed as a facility for sample irradiation and dosimeter calibration purposes because of its dose distribution which is more homogeneous than that of large-scale gamma irradiators. However, optimizing the calibration service requires an in-depth understanding of the dose mapping within the sample chamber. This study aimed to demonstrate the applicability of a simulation using the Monte Carlo (MC) Proton Heavy-Ion Transport Code System (PHITS) software for determining the dose distribution within the GC-5000 irradiator at the Institute of Nuclear and Chemistry Technology (INCT), Poland, to validate the results in experiments using alanine dosimetry. Five measurement points were defined, with each point carrying four alanine dosimeters simultaneously irradiated in an in-house phantom manufactured from polymethyl methacrylate (PMMA). The in-house phantom and alanine dosimeters were additionally simulated with PHITS. The GC-5000 chamber was modeled consistently with the original GC-5000 design, which included the configuration of 44 Co-60 pencil sources and their activities. The relative differences between simulation and experiment for the five-point measurements were 0.7 % and 7.0 % for the minimum and maximum, respectively. The position with the best agreement was at the centre of the in-house PMMA phantom. It was found that the results of the MC simulation and the experimental dose mapping agreed. It is concluded that both methods can be used to precisely determine the dose rate at defined positions within the GC-5000. It is concluded that the methodology developed in this study, i.e., the integration of MC modeling and alanine dosimetry, provides a validated and practical approach for dose mapping and may serve as a reference for similar compact irradiators used in radiation processing. The methodology can also be extended to optimize other industrial radiation processing facilities, as it provides a robust framework for accurate dose calibration and dose rate mapping.