Caracterização computacional de um laboratório de calibração de detectores de fontes de nêutrons

Abstract

The objective of this study was the computational characterization of a new neutron detector calibration laboratory at METROBRAS (LCDNM). In this study, the MCNP6.3 radiation transport code was used to characterize the laboratory's radiation fields. The neutron irradiation system consists of two neutron sources: americium-241-beryllium (²⁴¹AmBe) and californium-252 (²⁵²Cf). Although the laboratory does not have a 252Cf source, it was included in the simulations to provide useful information for its possible allocation in the future. The main qualitative and quantitative aspects indicate that the spatial distribution and attenuation of neutron fluence in the laboratory vary according to the distance from the source, with the ambient dose equivalent rate and neutron fluence decreasing as the distance increases. Five environmental scenarios were simulated: complete, evacuated, air-filled, without walls, and without a floor. The results showed that the complete and floorless conditions presented the highest dose rates. The obtained results were consistent with the literature, confirming the reliability of the computational simulations. The ambient dose equivalent rates for all neutron equipment in the laboratory varied as expected, ranging from 1.08E4 µSv/h to 2.18E1 µSv/h for the ²⁴¹AmBe source and from 1.34E6 µSv/h to 2.41E3 µSv/h for the ²⁵²Cf source, depending on the distance. The neutron fluence also exhibited the expected behavior, with values ranging from 8.70E3 cm⁻²s⁻¹ to 1.96E1 cm⁻²s⁻¹ (²⁴¹AmBe) and from 1.17E6 cm⁻²s⁻¹ to 2.49E3 cm⁻²s⁻¹ (²⁵²Cf). The overall consistency of the results with previous studies reinforces the accuracy of the simulations performed for the laboratory, ensuring the reliability of the radiation field characterization.