Two types of single sphere neutron spectrometers based on micro-structured semiconductor neutron detectors

Abstract Two types of single sphere neutron spectrometers based on a set of micro-structured semiconductor neutron detectors (MSNDs) were designed. Each neutron spectrometer consists of 31 MSNDs symmetrically located at certain positions along three perpendicular axes within a single moderating sphere. One uses high-density polyethylene (HDPE) moderating sphere, while the other uses borated polyethylene rather than HDPE as the outermost thin shell of moderating sphere. The second design aims to eliminate the backscattering effects in order to improve the response isotropy of slow neutrons. For two neutron spectrometers, a charged particle tracking (CPT) model was built with Monte Carlo transport code MCNPX to calculate neutron responses for 53 mono-energies from 10 -9 MeV to 20 MeV for three different irradiation geometries. The feasibility of two neutron spectrometers and the isotropy of neutron responses were evaluated by simulating a set of irradiation exposures to different typical neutron spectra. A generalized regression neural network (GRNN) method was used to unfold neutron spectra without the need to input preset spectral information by the users. The neutron spectrum unfolding performance was assessed quantitatively by index Q s and the results from two spectrometers were compared and analyzed.