Experimental and numerical characterization of the neutron field produced in the n@BTF Frascati photo-neutron source

Abstract

A photo-neutron irradiation facility is going to be established at the Frascati National Laboratories of INFN on the base of the successful results of the n@BTF experiment. The photo-neutron source is obtained by an electron or positron pulsed beam, tuneable in energy, current and in time structure, impinging on an optimized tungsten target located in a polyethylene–lead shielding assembly. The resulting neutron field, through selectable collimated apertures at different angles, is released into a 100 m 2 irradiation room. The neutron beam , characterized by an evaporation spectrum peaked at about 1 MeV, can be used in nuclear physics, material science, calibration of neutron detectors , studies of neutron hardness, ageing and study of single event effect. The intensity of the neutron beam obtainable with 510 MeV electrons and its fluence energy distribution at a point of reference in the irradiation room were predicted by Monte Carlo simulations and experimentally determined with a Bonner Sphere Spectrometer (BSS). Due to the large photon contribution and the pulsed time structure of the beam, passive photon-insensitive thermal neutron detectors were used as sensitive elements of the BSS. For this purpose, a set of Dy activation foils was used. This paper presents the numerical simulations and the measurements, and compares their results in terms of both neutron spectrum and total neutron fluence.