A neutron spectrometer has been developed to measure energy spectra of neutrons in the energy range from thermal to a few tens MeV. The detector consists of a spherical polyethylene moderator with a diameter of 30 cm and 19 pairs of ⁶Li- and ⁷Li-glass scintillators arranged along the orthogonal x-, y-, and z-axes of the sphere. The pairs can obtain the thermal neutron flux distribution in the sphere. The energy spectrum of the incident neutrons can be extracted from the information on the thermal neutron flux distribution in the moderator.

The detector characteristics have been examined with the Monte Carlo simulations and the experiments using monoenergetic neutrons. The response obtained by the experiments and that by the simulations show good agreement. The energy spectra of the monoenergetic neutron beams have been obtained by using the unfolding codes, SAND2 and J-log with the response function obtained with the simulations. In spite of white initial guess spectra, the unfolded energy spectra agree well with the true ones.