Instrument description

Reactor hall, hot beam H 8
beam size: 20 cm height x 5 cm width
Monochromators
size: 20 cm height x 18 cm width
variable vertical focussing
crystal spacing d flux /106 n cm-2 s-1 Ei/meV
Cu(200) 1.807 19 62


17 166
Cu(220) 1.278 6.0 207


4.8 414
Cu(331) 0.829 2.3 497


1.3 828
Collimation
Boron coated collimators
α2, α3, α4 = 20', 30', 40', 60'
Sample
beam size 7 x 4 cm2
Analysers
Cu(200); Cu(220)
each 12 cm height x 16 cm width
with variable vertical focussing
PG(002) 15 cm height x 23 cm width
with variable vertical and horizontal focussing
3He detector
 

N1 works in a time-sharing mode. This means that the same monochromator is also used by the Be-filter spectrometer IN1-BeF and by the liquids diffractometer D4. Changing over between the three different instruments can be done without difficulty in about two hours.

Either the three-axis spectrometer (TAS) and the Beryllium Filter-analyser (BeF). spectrometer can be connected to the instrument monochromator unit. The secondary spectrometers are mounted on "Tanzboden" modules with the possibility of varying the distance between the different modules. The interchange of these two secondary spectrometers does not take long time - about an hour. The two spectrometers of IN1 operate on the basis of time sharing of the common monochromator with the liquids diffractometer D4.

The monochromator unit carries three different vertically focussing monochromators built from copper single crystals (available reflecting planes Cu(200), Cu(220) and Cu(331)). The exchange of the monochromator planes is controlled by the instrument computer. The radius of curvature can be automatically adjusted as function of reflected energy in order to maintain maximal flux at the sample position in the course of energy scans.
The scattering angles on the monochromator cover a range of 10°<2M <90° allowing for scanning neutron energies from ~13 meV to more than 1 eV..

The IN1-TAS spectrometer: the scattering angles at the sample and the analyser can be changed in the intervals -115°<2θS<115° and -120°<2θA<120°. Three different analysers (PG(002), Cu(200), Cu(220)) can be installed in order to optimise intensity and resolution for a given experiment.
Various resonance absorption filters (e.g. Er, Sm, Hf ...) can be used to suppress higher order contaminations from the incident beam or in the scattered beam. An oriented Pyrolytic Graphite filter is designed for experiments eventually demanding thermal neutron energy range.

The IN1-BeF spectrometer: a Beryllium metal block cooled down to liquid nitrogen temperature is placed in between the sample and the counter. The role of this block is to scatter out all neutrons with energies higher than 5.2 meV (beryllium cut-off) thus permitting registration of only low-energy neutrons scattered by the sample. The Be-block is cut onto several rods along the sample-counter path with absorbing spacers between them in order to reduce residual transmission of higher energies through multiple scattering events in the Be-filter.
The sample unit allows for rotation of an oriented sample with respect to direction of incident beam. The scattering angle can be varied between -100° and +100° while in most cases (when sample is a polycrystal) the angle is kept fixed at about 90°.

The sample rotational tables on both spectrometers are compatible with majority of sample environment equipment at ILL: cryostats, cryo-furnaces, furnaces, cryo-magnets (non-magnetic goniometer is available), large-diameter vacuum box for experiments at low scattering angles etc.

A dedicated instrument control computer (DEC workstation Compaq PWS-500) running under Unix is installed with the same flexible software as available on the other three-axis spectrometers.