Contribution of the scattered radiation on the neutron beam fluence at the calibration laboratory of IPEN

Abstract

In recent years, an upsurge in demand for neutron calibrations has been experienced in Brazil and several other countries in Latin America, mainly due to the increase in oil prospection and extraction procedures. The only laboratory for calibration of neutron detectors in Brazil is located at the Institute for Radioprotection and Dosimetry (IRD/CNEN), Rio de Janeiro. This laboratory is the national standard dosimetry laboratory in Brazil. With the increase in the demand for the calibration of neutron detectors, the need for more calibration services became evident. In this context, the Calibration Laboratory of IPEN/CNEN, São Paulo, which already offers calibration services of radiation detectors with standard X, gamma, beta and alpha beams, recently projected a new calibration laboratory for neutron detectors. One of the main problems in this kind of calibration laboratory is related to the knowledge of scattered radiation. In order to evaluate it, simulations were performed without the presence of the structural elements and with the complete room. Thirteen measurement points were evaluated at various distances. As part of the characterization process of the radiation fields of the new Neutron Calibration Laboratory, this work presents results on the influence of the radiation scattered by the structural components of the room: walls, doors, ceiling and floor, in different calibration positions, on the detector response. Therefore, the neutron radiation attenuation and the scattering parameters were determined at different source-detector distances, through computational simulation, using the MCNP5 Monte Carlo code.