Design and optimization of a shield for Am-Be source to reduce radiation hazards using MCNPX code

 Protection against nuclear radiation is one of the most important issues in nuclear technology and industries that use this technology. Among the types of radiation emitted from radioactive sources, neutron and gamma rays are among the most dangerous radiations due to lack of electrical charge and serious damage to living tissues. The principal challenge in radiation protection is the proper design of a shield against neutron and gamma radiations. Hence, this study has investigated the improvement of the protection against these radiations. 

 This study is of applied-developmental and quantitative type. Calculations have been performed using the MCNPX code in this study, which is one of the strongest nuclear calculation codes. The data were analyzed using quantitative statistics and ORIGIN software (OriginLab company, 1992, Northampton, Massachusetts, USA). 

 Based on the results, utilizing the spherical geometry had a better performance to increase the neutron fluxes in comparison with the cylindrical and cubic geometries. Moreover, polyethylene with high density was selected as the best moderator. Ultimately, it was dealt with the comparison and selection of the best protection to minimize the produced gamma rays due to the absorption of neutrons in different materials used by the source and neutrons that run away from the outer surface of the source configuration. 

 Using the composite sphere of paraffin and polyethylene with high density up to a radius of 12 cm and tungsten with a thickness of 1 cm was suggested as the final configuration for the aim of this study. In comparison to the no-protection mode, this protection is effective to 74% in reducing the neuron dosage and 55% in reducing the primary gamma-ray, while the mentioned protection is about 72%–73% effective in reducing the general dose.