Validation of an indium-based multi-shell neutron spectrometer

A multi-shell neutron spectrometer with indium foil detector (In-MuNS) was developed to evaluate intense neutron fields that are generated in medical accelerators. The response matrix of this new spectrometer was calculated from 1 meV to 100 MeV using MCNP5 v.1.6 with ENDF/B-VIII.0 nuclear data. An experiment with a(252)Cf source with known emission rate was performed to validate the computational model of the spectrometer. This included detailed modelling of the irradiation room to evaluate the room-scattered field. The contribution of scattered neutrons to the induced activity in the foil reached 30% for the smallest sphere configuration (diameter 5.0 cm). The quotient between the experimental and simulated foil activity remained satisfactorily constant (1.03 +/- 0.04) as the sphere diameter varied, demonstrating the validity of the simulation model. In-MuNS proved to be a portable and compact alternative to conventional Bonner spheres.