A modular neutron irradiator based on 241Am-Be neutron sources

Abstract

Neutron irradiator facilities with 241Am-Be sources are worldwide used in order to perform neutron activation analysis (NAA), to investigate materials in different research areas or to test and calibrate neutron detectors and environmental or personal dosemeters. The use of a neutron irradiator is advantageous because of its very stable neutron flux, even it is many orders of magnitude lower than the one of a nuclear reactor or a particle accelerator. Most of irradiators are realized with neutron sources located at fixed positions and accordingly the characteristics of neutron spectrum previously assessed do not change. Therefore, an interesting choice is to have a modular facility, capable of varying conditions of irradiation and setting the prevalence of fast or thermal neutron spectrum component. In this work we describe the design and the realization process of a new modular 241Am-Be neutron irradiator in order to obtain a neutron energy distribution useful to test neutron detectors or personal dosemeters. Some of the useful calculations oriented to optimize thicknesses and shape of the moderators and shielding materials were obtained with a Monte Carlo simulation with MCNP5 code. The new modular neutron irradiator will provide an useful facility for radiochemical material studying and testing and calibration of personal dosemeters or neutron measurement equipments. Irradiation tests and neutron fluxes measurements by using various measurement devices, as activation materials, irradiation of bare and cadmium covered gold foils, bubble dosemeters, are also reported.