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Iris

Workhorse high-resolution spectrometer at ISIS

This instrument is operational .

IRIS is a time-of-flight inverted-geometry crystal analyser spectrometer designed for quasi-elastic and low-energy high resolution inelastic spectroscopy.

Neutrons scattered from the sample are energy-analysed by means of Bragg reflection from one of two large single crystal arrays (pyrolytic graphite and muscovite mica) in close to backscattering geometry. Each analyser is associated with its own bank of 51 ZnS scintillator detectors. The two analyser banks, which can operate simultaneously, afford high resolution over wide energy and momentum transfer ranges.

In addition, a 25 K beryllium filter is also available when using the graphite analyser to extend the accessible energy transfer range. Furthermore, the graphite analyser bank itself is cooled close to liquid helium temperature to reduce background contributions from thermal diffuse scattering.

The diffraction detector bank at two theta ~ 170° can be used either as a diagnostic tool for samples under spectroscopic study or as a dedicated long d-spacing diffractometer with good resolution and high intensity.