Analysis by Monte Carlo methods of the response of an extended-range Bonner Sphere Spectrometer

High-energy neutrons up to 230 MeV are generated as a consequence of (p,n) nuclear reactions in proton therapy facilities. The aim of this work is to evaluate the potential extension of the UPM Bonner Sphere Spectrometer (BSS) through the use of spallation materials, for its future application to determine neutron fluence spectra in such facilities. Monte Carlo methods have been used to model the response of the actual and modified spheres with the introduction of a spallation material layer, lead or copper, analyzing their response functions. An analysis is also made of the neutron fluence spectra over the ⁶LiI(Eu) scintillator volume and the uncertainty that can be associated to the response functions at high energies as a consequence of the different physics models that can be applied for their analysis.