guide hall n°1, thermal guide H25 | Neutron interferometer with USANS option | monochromator | two crystals mounted on a computer controlled support
| type I
| silicon perfect block crystal
| reflecting planes | [111], [220], [113], [331] | wavelenght range | 0.6 Å < λ <4 Å | type II
| channel-cut silicon perfect silicon crystal | reflecting planes | [220], [331] | wavelenght range | 1.6 Å < λ <2.9 Å | Beam cross section | 2 x 5 cm2 | interferometry | Large perfect Si crystal interferometers of different designs | coherent beam-separation | 2 - 5 cm | enclosed area | up to 100 cm2 | path lengths | 10-21 cm | performance of a [220] skew symmetric interferometer at 1.84 Å with beam area 1x1 cm2 | flux in front of interferometer | 16000 n cm-2 s-1 | flux in O-bean and H-beam | 7000 n cm-2 s-1 | contrast in O-beam | 90% | wavelength spread Δλ/λ | 2.4% | beam divergency | 0.75° | ultra small-angle neutron scattering (USANS)
| Bonse-Hart camera | type | 6-fold [220] Bragg reflection with tail suppression | peak intensity | 10000 n cm-2 s-1 | angular resolution | 0.01 sec arc | momentum resolution | 1.5·10-5 Å-1 | signal to background ratio | > 105 | polarised neutron option | polariser type | double magnetic prism deflection | polarisation | > 99.5 % | beam cross section | 1 x 1 cm2 |
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S18 is a dedicated neutron optics instrument. The neutron optical bench instrument is installed at the super-mirror guide H25 at the first experimental position. Two different silicon crystal monochromators (a block crystal and a channel-cut triple bounce crystal) can be put into the beam which allows two different modes of operation: the interferometer (IFM) and the ultra small-angle scattering (USANS) option. The silicon monochromator and the interferometer crystals (or the USANS analyser crystal) are arranged in a non-dispersive arrangement which guarantees highest possible intensity and resolution.
IFM option
For the IFM option a set of various silicon interferometers are available primarily for neutron scattering length measurements and quantum optical investigations. As a standard interferometer a skew symmetrically cut silicon crystal with mean visibility of up to 90% operating at a typical wavelength of 1.9 Å at a Bragg angle of 30° is used. Large double loop interferometers with beam path lengths of 21 cm and beam separation of 5 cm working at a wavelength of 2.7 Å under Bragg angle of 45° are used for several novel quantum measurements, e.g. topological quantum phases, quantum state reconstruction and quantum contextuality experiments. Polarised neutrons can be used when a prism polariser is inserted between monochromator and interferometer. A third axis is available for a momentum and polarisation analysis of the beams leaving the interferometer.
USANS option
In the USANS option two triple bounce crystals (as monochromator and as analyser) form a so-called Bonse-Hart camera. The 6-fold reflection and the so-called Agamalian-cut give a peak to background ratio better than 105. The instrument covers a Q-range 2.10-5 < Q < 5.10-2 Å-1 which allows a clear overlap with standard pinhole SANS instruments.
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