IN10 is designed for inelastic or quasielastic scattering experiments requiring very high energy resolution (up to dE ~ 0.3 microeV) and moderate momentum transfer resolution. IN10 owes its high energy resolution to the use of nearly perfect backscattering both at the monochromator and at the analyser crystals. The instrument can be adapted to a range of experimental problems by a suitable choice of monochromator and analyser crystal combinations. Typically for quasi-elastic scattering, one uses monochromator and analyser crystals of the same lattice spacing and orientation. Alternatively, one can select a combination which allows one to measure in a specific range of inelastic energy transfers.

IN10 is an inverse geometry instrument in which the energy transfers are scanned by varying the incident energy whilst keeping the final energy fixed. The incident energy is changed either by Doppler shifting the neutron wavelength (IN10A) or by thermal expansion of the monochromators (IN10B).

About 40% of the monochromatic beam is extracted using a (002)-orientated pyrolytic graphite deflector crystal. This beam enters a supermirror guide, then passes through a chopper disk, a monitor and an adjustable diaphragm before reaching the sample.

The analyser crystals are mounted on spherically-hollowed backing plates (radius of curvature 1.5 m) which subtend appreciable solid angles at the sample position. Therefore only moderate resolution in momentum transfer may be achieved. Neutrons which are back-scattered from the analyser crystals arrive at 7 detectors which are placed around the sample position. Neutrons that are directly scattered from the sample into the detectors are eliminated by gating the data acquisition according to the phase of the chopper disk.

The instrument offers two Si(111) crystal analyser options which both reflect 6.27 Å neutrons in backscattering :

• the polished crystals can cover up to 0.7 sr within the scattering angle range 45° < 2θ <160°. They are virtually flawless. An energy resolution width down to 0.3 µeV (FWHM) is achievable when they are used in combination with a polished monochromator;
• the unpolished crystals cover a solid angle up to 1.8 sr (including the small angle range). They have enhanced surface strain allowing higher intensity measurements at a relaxed energy resolution of typically ~ 1 µeV FWHM.

In addition, an unpolished Si(311) setup is available (wavelength 3.275 Å) :

• The set of unpolished Si(311) crystals covers a solid angle up to 1.2 sr in the range 45° < 2θ < 160°. When used in conjunction with a Si(311) monochromator, quasi-elastic measurements are possible at increased momentum transfers up to 3.7 Å^-1.