Wide angle NSE: the multidetector spectrometer SPAN at BENSC

The magnetic held configuration of the spectrometer SPAN allows simultaneou s NSE measurements to be performed over a particularly large angular range. The NSE precession field is created by three pairs of coils with diameters 1, 3 and 4.8 m, respectively, and the set-up has a symmetry axis, which is perpendicular to the scattering plane and crosses the sample position. The resulting magnetic held integral does not change with the scattering angle and thus fulfils the condition for multidetector NSE. In order to preserve the symmetry of the magnetic field, remanent supermirrors are used as anal yzers. These supermirrors perform in reflection, in the stray magnetic fiel d of the precession coils, and are mounted on analyzer frames with an angul ar opening of 25.7 degrees each. The neutron optical elements (analyzer, po larizing guide) of SPAN have a high transmission over a large wavelength ba nd. As a consequence of this, NSE can be done for incident wavelengths rang ing from 2.5 to 9 Angstrom. At the lowest wavelengths high q values can be reached, which were not previously accessible for NSE experiments (at lambd a = 3 Angstrom: 0.08 Angstrom(-1) less than or equal to q less than or equa l to 4 Angstrom(-1)). (C) 2000 Elsevier Science B.V. All rights reserved.