Determination of neutron energy spectra inside a water phantom irradiated by neutrons of energy up to ~ 64 Me V

Includes bibliographical references. .A neutron spectrometer based on an NE230 deuterated organic liquid scintillator (25 mm diameter x 25 mm) has been developed for measuring neutron spectra in water. The spectrometer is capable of measuring neutron energies above 5 MeV, set by the electronic threshold. An important feature of the spectrometer is that it is able to discriminate between recoiling protons that are associated with neutron interactions that take place in the detector from recoiling protons that arise from n-p scattering in the water. The spectrometer was tested by recording pulse height spectra in a water phantom irradiated by neutrons of energy up to ~ 64 MeV. Neutron energy spectra were obtained from the pulse height spectra by Bayesian unfolding with the code MAXED using a response matrix that was determined experimentally. The efficiency of the NE230 detector was determined experimentally relative to an NE213 detector of known efficiency. A series of detailed measurements was taken at positions in the phantom along the axis of the neutron beam while exploratory runs were made off the beam axis. Results from measurements made along the axis of the neutron beam compare well with Monte Carlo calculations using MCNPX