Neutron and gamma-ray radiation fields characterisation in a 241Am–Be irradiator in view of its use as research testing tool

A neutron irradiation facility based on four 241Am–Be sources, each one with an activity of 111 GBq, placed in Plexiglas pipes inside a tank filled with water used both as a moderator and a biological shielding, has been realized at the Engineering Department of Palermo University. In view of its use as a testing tool in various research activities, a characterisation of the irradiator has been carried out through the determination of neutron and gamma-ray flux profiles, the evaluation of the thermal to total neutron flux percentage ratio and of the epithermal neutron shaping factor. To this aim, results of a Monte Carlo (MCNP5 code) simulation based on a previously validated source model have been compared with the experimental results obtained from TLD dosimeters and activated gold foils. Experimental values show a good agreement with MCNP5 evaluations, highlighting a gradually decreasing of dose values as a function of the distance from the lying plane of sources. Maximum values of experimental neutron fluxes have been found to be (3.73 ± 0.38) × 104 cm−2 s−1 (thermal) and (2.13 ± 0.25) × 104 cm−2 s−1 (epithermal and fast), with a percentage of 64% of thermal to total neutron flux and epithermal neutron shaping factor equal to −0.16 ± 0.04. Both neutron and gamma fluxes for the most used positions inside the irradiation channel can then be provided and the main parameters for any irradiation plane can be easily established