Spectroscopic characteristics of the OSIRIS near-backscattering crystal analyser spectrometer on the ISIS pulsed neutron source.

The OSIRIS neutron instrument on the ISIS pulsed source now affords the option of high-resolution quasi-elastic and inelastic neutron spectroscopy. In this paper, the performance of OSIRIS is presented, with the spectroscopic characteristics of the instrument being discussed in terms of energy resolution, signal to background ratio and neutron count rate. Recent improvements to the spectrometer are described, in particular the effect of cooling the crystal analysers close to liquid helium temperature to enhance the sensitivity of the instrument. The performance of OSIRIS is also likened to back-scattering, crystal analyser spectrometers at other neutron sources.