CRG - cold neutron three-axis spectrometer

Guide hall n°1, cold guide H144

115 m from the vertical cold source
guide dimensions 45 x 105 mm2 with tapering towards guide end: 20 x 140 mm2


PG (002); d = 3.355 Å
height x width: 20 x 16 cm2
with variable horizontal and vertical curvature


transmission polariser (cavity, guide changer 35m in front of guide end)

working range

2 - 6 Å


> 95 %

flipping ratio

20 - 27 (depending on energy)


PG (002)
(with variable horizontal curvature; 12.2 x 11.8 cm2)
for polarization analysis: Heusler (111)
(d = 3.44 Å; 7.5 x 14.5 cm2)

Double focusing set up

horizontal divergence at sample position: 2-3o;


Gadolinium coated Soller collimators with divergences of 10', 20', 30', 40', 60', 80' can be placed before sample, analyser, and detector

3He detector

vertically mounted 12 cm high, 5 cm Ø

Instrument description

The monochromator of IN12 is a set of horizontally and vertically focussing pyrolytic graphite (002) crystals, which deliver the following incident wavelengths, energies, and wavevectors: 

  • 1.26 < λ/Å < 6.3
  • 2.1 < Ei/meV < 42
  • 1.0 <  ki/Å-1 < 5.0

Measurements with a calibrated monitor at the sample position show for a typical wavevector of ki=2Å-1 a flux of about:

  • double focusing set up: 1.04 x 108 n cm-2 s-1
  • velocity selector in: 8.4 x 107 n cm-2 s-1
  • velocity selector, 60' collimation: 5.02 x 107 n cm-2 s-1

Due to the double curvature of the neutron guide there is little λ/2 contamination for wavelengths shorter than 2.5 Å. At longer wavelengths a velocity selector placed far upstream in the guide is used as a filter.

The sample is mounted on a motorized, non-magnetic goniometer which may achieve tilts of ± 20°. Two analysers are available: PG (002) for unpolarized work; and a Heusler (111) for polarization analysis.

For use with polarized neutrons a supermirror bender can be mounted after the first collimator to polarize the incident beam. A curved Heusler (111) analyser replaces the normal analyser. A small field (< 15 Oe; magnitude and direction computer controlled) may be imposed at the sample position using a system of coils or a super-conducting magnet can be used to produce larger fields.

The monochromator covers an angular range of -10°< 2θM < -140°.

The sample covers an angular range of -120° < 2θS < 120°.

The analyser covers an angular range of -140° < 2θA < 140°.

The energy resolution with 30' collimation is 22; 75; and 110 µeV (FWHM) for incident energies of 2.3; 4; and 5 meV, respectively.
In double focusing set up the resolution results to 150 µeV (FWHM) for an incident wavevector of ki=1.5Å-1.