CRG - thermal neutron backscattering spectrometer

Guide hall n° 1, thermal guide H24



temperature range

-196 < TM/°C < 250

energy range

-125 < ΔE/µeV < 150

angular range

81° < θM < 89°

incident energy (TM≥25°C)

16.45 meV

incident wavelength (TM≥25°C)

2.23 Å

energy resolution

8 µeV


pyrolytic graphite with variable curvature


sample size

3.5 x 3.5 cm2

flux at sample

2 x 104 n cm-2 s-1




0.2 < Q-1 < 4.9


ΔQ/Å-1 < 0.1




35 3He detectors

1 <Q/Å-1 < 4.9

3He PSD detector

0.2 <Q/Å-1 < 0.8

background per detector

0.5 - 4 cpm

Sample environment


300 < T/K < 1900


2 < T/K < 500


5 < T/K < 550

Instrument description

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.