Phased Rotating Crystal and Chopper for Time of Flight Neutron Spectroscopy

Abstract

A slow neutron spectrometer that uses a rotating single crystal to chop and monochromate the reactor neutron beam is described. A high transmission mechanical chopper is operated in phase with the rotating crystal to eliminate undesired crystal reflections, higher order contamination, and to suppress the background of time uncorrelated neutrons. Pulsed neutron beams of high quality can be obtained from the thermal energy range to greater than 0.5 eV. Energy widths as low as 1% with burst widths around 7 μsec can be attained at 0.3 eV. Intensities are adequate for inelastic scattering studies. The spectrometer is designed primarily for downscattering measurements. Scattering measurements are conducted in a completely shielded scattering chamber with eleven scattered neutron detectors arranged at scattering angles of 15° to 165°. Time of flight techniques are used to determine the scattered neutron spectra. The design, construction, and performance characteristics are given. Some representative measurements made on zirconium hydride are presented.