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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 a252Cf 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. • A portable and flexible design for passive neutron spectrometry system is presented. • An indium-based multi-sphere neutron spectrometer (In-MuNS) was developed. • The In-MuNS computational model was validated using a252Cf source. • Scattered neutron in the validation experiment was analyzed. [ABSTRACT FROM AUTHOR]

A new type of compact multi-shell neutron spectrometer (MuNS) was developed at PNRI. It consists of a series of concentric polyethylene shells that can be combined to form Bonner spheres with different diameters ranging from 5 cm to 30 cm. With respect to conventional Bonner spheres, this system is more flexible and portable. MuNS can accommodate either passive or active neutron detectors. The response matrix of the MuNS with a cylindrical 3 He proportional counter (He-MuNS) was calculated using Monte Carlo simulations for incident neutrons with energies ranging from 1 meV to 100 MeV. Anisotropy effect was investigated through simulations and is found to be at most 90% for the smallest configuration, indicating that He-MuNS should have a specific orientation during deployment. Validation of the calculated response matrix and calibration of the He-MuNS system were performed using a 252Cf reference source and the shadow cone method. The quotient of the measured and calculated neutron counts in the 3 He detector was computed for every sphere and the value was found to be constant within 5.1%. Results confirm the validity of the He-MuNS model and the simulated response matrix. [ABSTRACT FROM AUTHOR]

A portable neutron spectrometry system was designed based on thermal neutron detectors embedded in concentric polyethylene spherical shells. The system is flexible and can accommodate the use of either active or passive neutron detectors in different configurations. In this work, the response matrix of the system with In-115 foil detectors was calculated with MCNP5 v.1.6. Activation foils were chosen as an ideal detector for the planned use of the system in medical accelerator environments. Calculations were performed using ENDF/B VII.0 and ENDF/B VIII.0 data libraries. The response functions calculated with the two libraries differ by as much as 11.6% in the thermal energy region for the largest moderator. A sensitivity analysis was also performed to evaluate the effect of main design parameters on the response matrix. • A portable neutron spectrometry system (PNSS) that can accommodate neutron detectors in various configurations is designed. • The current work focused on indium activation foils due to its advantages as a passive thermal neutron detector. • Response functions calculated with ENDF/B VIII.0 and ENDF/B VII.0 deviate by as much as 11.6% for the largest moderator. • The effect of relevant design parameters on the PNSS response matrix is negligible within a certain range. • PNSS provides an alternative flexible configuration for Bonner sphere spectrometers. [ABSTRACT FROM AUTHOR]