Computational Modeling of The Brazilian Army Gamma Calibration Laboratory Using the MCNP Transport Code

Abstract

The Brazilian Army's responsibility for nuclear defense operations, as defined in the National Defense Policy and Army Strategic Plan, has led to advancements in this field, as the establishment of the Gamma Monitor Calibration Laboratory (LCG) at the Institute of Chemical, Biological, Radiological, and Nuclear Defense (IDQBRN) within the Brazilian Army Technology Center (CTEx). The LCG calibrates radiation monitors for troops in defense operations and emergencies. It has secured accreditation from the Evaluation Committee for Testing and Calibration Services (CASEC) and is currently seeking certification from the National Institute of Metrology, Standardization, and Industrial Quality (INMETRO) to enhance its Cs-137 calibration capabilities for radiological protection. All activities must adhere to relevant ABNT NBR standards. The primary aim of this paper is to develop a computational model of the LCG that integrates the irradiation system, utilizing the Monte Carlo N-Particle (MCNP) radiation transport code. This model will initially be employed to evaluate backscattered radiation and will remain available for future applications and testing. This simulation was performed using MCNP5, and the graphical input file editor (VISED) was used to verify the defined geometry. The modeling was based on construction data and the specifications of the internal equipment. The input file was created and utilized in the code, providing the output file with the ambient dose equivalent normalized per photon emitted at the source. Then, the result was adjusted for source activities and converted into a dose rate. All simulated values ​​were lower than the experimental ones, for example, for the condition without attenuation at 1 m, the simulated value is 3,0816 mSv/h, while the experimental is 3,1930 mSv/h.