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CRG - cold neutron three-axis spectrometer IN12

The cold neutron 3-axis spectrometer IN12 is a three-axis spectrometer with polarization analysis. IN12's gain over the "thermal" instruments is primarily in the long wavelength range. For polarization analysis, a supermirror bender can be mounted between the monochromator and the sample, and used in conjunction with a Heusler analyzer crystal.

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Instrument description

guide hall n°1, cold guide H142  (instrument currently being moved to H144)

108 m from the source
beam dimensions 12 x 3 cm2

Monochromator

PG (002); d = 3.355 Å
height x width: 12 x 8 cm2
with variable vertical curvature

Polariser

supermirror bender

aperture

4.5 x 3.7 cm2

polarization

> 95 %

transmission (for correct spin state):

50-60 % (depending on energy)

Analyser

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

Collimation

guide: α1 = 52/ki (min Å-1);

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

3He detector

vertically mounted 12 cm high, 5 cm Ø

Warning This page is outdated since the instrument is currently being moved to the end of the cold neutron guide H144. This will provide a significant improvement of the characteristics of the instrument.


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

2.3 < λ/Å < 6.0
2.3 < Ei/meV < 14
1.05 <  ki/Å-1 < 2.6

The gain in flux over thermal neutron instruments is greatest for wavelengths longer than 3.5 Å :

with Be-filter for Ei = 4 meV and
- 30' collimation: 7.4 x 106 n cm-2 s-1;
- 60' collimation: 1.0 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 4 Å. At longer wavelengths a liquid nitrogen cooled beryllium filter of 10 cm length may be 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 15°< 2θM < 90°.

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.

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