[ Identification | Description | Input parameters | Links ]

# The `ILL_IN13` Instrument

IN13 Thermal neutron backscattering spectrometer (without guide)

## Identification

- Site: ILL
- Author: E. Farhi and A. Dennison
- Origin: ILL
- Date: March 25, 2015

## Description

    IN13 Thermal neutron backscattering spectrometer (without guide)

    Because of its high energy resolution and high momentum transfer the
    backscattering spectrometer IN13 is particularly useful for the microscopic
    study of single particle motions (jump reorientation, rotational and
    translational diffusion, tunnelling) observed by incoherent neutron scattering.

    The high energy resolution of the order of a few μeV together with the
    availability of high momentum transfer (Q<4.9 Å-1) makes the spectrometer IN13
    particularly useful for the microscopic study of single particle motions (jump
    reorientation, rotational and translational diffusion, tunnelling) observed by
    incoherent neutron scattering. The instrument partly fills the gap of (Q, ω)
    space between IN10 and IN5.

    Temperature gradient monochromator
    The monochromator and analyser CaF2(422) crystals are oriented in near
    backscattering geometry thereby achieving an energy resolution of a few μeV. The
    energy of the incident neutrons is scanned by variation of the temperature of
    the monochromator at a fixed Bragg-angle. In an optional mode the 10 mm thick
    monochromator crystals are kept at a fixed temperature gradient and energy
    variation is performed by scanning the monochromator Bragg-angle. This achieves
    an increased flux at the sample position and slightly increases the energy
    resolution width.

    A vertically curved Graphite deflector focusses the beam onto
    the sample. The scattered neutrons are energy analysed by a set of seven
    spherically curved composite crystal analysers, each covering a large solid
    angle of 0.18 sr. An additional three circular analysers centred around the
    transmitted beam cover the small-angle region.

    The neutron time-of-flight is used to suppress (i) the background of neutrons
    scattered directly from the sample into the detectors and (ii) second order
    contamination. The neutrons are counted with a cylindrical multidetector
    consisting of 35 3He detector tubes, arranged in staggered circular rows. The
    small Q range from 0.2 to 0.8 Å-1 is covered by a 3He Position Sensitive
    Detector (PSD) arranged to see the circular analysers in exact backscattering.

    Monochromator: CaF2(422)
    temperature range:  -125 < ΔE/µeV < 150
    angular range:       81° < θM < 89°
    incident energy:     16.45 meV (TM≥25°C)
    incident wavelength: 2.23 Å
    energy resolution:   8 µeV

    Deflector: PG(002)

    Sample: here incoherent elastic scatterer (Vanadium)
    sample size          3.5 x 3.5 cm2
    flux at sample       2e4 n cm-2 s-1 (when fed from H24, NOT in this model)

    Analyser: CaF2(422)
    Q-range:             0.2 < Q/Å-1 < 4.9
    Q-resolution:        ΔQ/Å-1 < 0.1

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
RMV | m | monochromator vertical curvature. Use 0=flat, -1=auto. | 0
RDV | m | deflector vertical curvature. Use 0=flat, -1=auto. | 4.6
RDH | m | deflector horizontal curvature. Use 0=flat, -1=auto. | 0
TM | K | monochromator temperature, from 77 to 500 K | 301
LMD | m | monochromator-deflector distance | 1.8
mos_ana | arcmin | analyser mosaic | 2
CaF2mos | arcmin | monochromator mosaic | 10
gW |  |  | 0.030

## Links

- Source code for `ILL_IN13.instr`.
- The IN3 TAS at the ILL

[ Identification | Description | Input parameters | Links ]