Sviluppo di un fotoconvertitore per neutroni epitermici basato su un acceleratore lineare di elettroni a 18 MeV per il progetto e-LiBaNS

A neutron irradiation facility based on a 18 MeV electron Linac has been built at the Physics Department of Turin University, within the INFN e-Libans project. The Linac can give as an output both a monoenergetic electron beam or a gamma beam with a bremsstrahlung spectrum. The neutron production is achieved coupling the Linac with a dedicated photo-neutron converter, in which fast neutrons are ob- tained. Fast neutrons are then moderated down to the desired energy range and concentrated inside an irradiation volume. In the first part of my thesis work, I have exploited the MCNP6 simulation code to develop an epithermal version of the photo-neutron converter. The various step that brought to the construction of the final version of this prototype are described. Some features of the source consist in the possibility to modulate the neutron field parameters by varying the onverter geometry and materials. The second part of this thesis is dedicated to the in situ measurements of the epithermal neutron field using as fluencemeter a compact detector developed within the e-LiBaNS collaboration, named EPI 3. The neutron spectrum inside the photo converter cavity has been measured by means of a calibrated Bonner Spheres spectrometer System (BSS) using as inner detector a TNRD of the e-LiBaNS project. EPI 3 and the BSS are capable of operating in intense and pulsed neutron fields, with low sensibility to photons. In the last chapter a summary of the experimental results is given. A uniform epithermal fluence rate of the order of 10^5 cmùì(-2) s^(-1) has been achieved. The energy spectrum measurement confirmed the dominance of the epithermal component with low thermal (< 1 %), fast (< 7%) and gamma contamination.