Diffraction Group

The ILL Diffraction instrument group studies the structure of a wide range of materials. The influence of structure is indeed everywhere; the properties of water and ice, the hardness of metals, the strength of magnets, and even the biology of DNA or the effect of antibodies on viruses – all depend on structure. Neutron diffraction instruments are used to provide detailed insights into the arrangement of atoms within a material, helping scientists to understand its properties and behaviour.

We generally use a large monochromator to select a particular neutron wavelength (just as the different wavelengths of light can be separated using a prism or fine grating). The material to be studied is placed in this monochromatic neutron beam, and the scattered neutrons are collected on a large 2D detector. The sample can be a liquid, a bunch of fibres, a crystal or a polycrystal. A polycrystal is the usual form of solid matter, such as a lump of metal or ceramic, and is made up of millions of tiny crystals.

How does it work? When a polycrystalline lump of material, often ground to a fine powder, is placed in the beam. Neutrons are scattered at specific angles, corresponding to the spacing between atomic planes, and by measuring these angles and intensities the atomic structure of the material can be deduced. If instead of a crystalline powder an amorphous or liquid sample is used, there are only broad peaks at specific angles corresponding to average interatomic distances. To obtain more data, short neutron wavelengths are used, and sometimes one type of atom is replaced by its isotope – chemically identical, but with a different nucleus and different neutron-scattering power – this difference then gives information specific to that atom.

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Diffraction group instruments

The ILL's diffraction instruments are divided into two main groups: powder diffractometers and single-crystal diffractometers. In this page you will find a very short description of our instruments. If you are interested in more detailed information, you can consult the official page of the instrument (mantained by each Instrument Scientist).

These two-axis diffractometers are used to investigate the structure of powders, liquids and amorphous materials. Diffraction group machines use relatively short wavelength neutrons (0.3 to 2.0 Å) to resolve structures to atomic resolution, in contrast to diffractometers in the Large Scale Structures (LSS) group that use long wavelength neutrons for lower resolution of larger structures.

Usually a large composite monochromator, up to 300 mm high, is used to select a narrow band of wavelengths and focus it onto the sample.The monochromator may be made from several crystals of pyrolytic graphite, copper or germanium. Large multi-detectors and linear position-sensitive detectors (PSDs) cover a large solid angle for maximum efficiency.

The two high-resolution powder diffractometers D1A and D2B are used mainly for Rietveld refinement, with scans lasting from 30 minutes to several hours. They are complemented by two high-flux medium-resolution powder machines, D1B and D20, which are used mainly for temperature scans and other types of fast experiment, especially on small samples. D4, on the short wavelength hot source, is used for liquids and amorphous materials, together with D20.

D1B 2-axis diffractometer (CRG)
D2B high-resolution 2-axis diffractometer
D4 diffractometer for liquids and amorphous substances
D7 diffuse scattering spectrometer
D20 high-flux 2-axis diffractometer

D20 Diffraction Magnetism and quantum materials, Chemistry of materials, Energy

D20 is very high intensity 2-axis diffractometer equipped with a large microstrip detector. Due to the extremely high neutron flux, it opens up new possibilities for real-time experiments on very small samples.

D7 Diffraction Magnetism and quantum materials, Chemistry of materials

D7 has been dismantled. The new permanently-polarized diffuse scattering spectrometer is D007. The diffuse scattering spectrometer D7 is a general purpose cold neutron polarisation analysis spectrometer, designed to study nuclear and magnetic short range ordered materials and magnetic defect structures.

D4 Diffraction Energy, Environment, Soft matter and polymers

D4, a two-axis diffractometer, uses short-wavelength neutrons from the hot source to measure diffraction patterns over a large Q-range. Combining very high counting-rate stability with very low background counts, D4 can determine the local atomic structure of disordered materials (liquids, amorphous solids, nano-structured materials, disordered crystals) with excellent accuracy.

D2B Diffraction Magnetism and quantum materials, Chemistry of materials, Engineering, Energy

D2B is a very high-resolution powder diffractometer designed to achieve the ultimate resolution (limited only by powder particle size, Δd/d 5x10-4). The instrument is built in such a way that an alternative high flux option (with resolution comparable to that of D1A but much higher intensity) can be chosen at the touch of a button.

D1B Diffraction Magnetism and quantum materials, Chemistry of materials, Engineering, Reactions and catalysis

D1B is a high-intensity powder diffractometer equipped with a Position Sensitive Detector (PSD) covering an angular range of 0.8° to 128.8°. Thanks to its highly efficient detector, it is in high demand for real-time experiments and very small samples. D1B operates as a CRG-A instrument managed jointly by CNRS and CSIC.

Powder diffraction instrument parameters

	D1B		D2B		D4			D7			D16	D20
λ (Å)	1.28		1.594		0.35	0.5	0.7	3.1	4.8	5.7	4.5 & 7.5 (83°)	1.3	2.41
2qmin	2.2	2.2	5.5	5.5	1.3	1.3	1.3				5.6 & 9 (115°)	3.1	3.1
2qmax	128.5	128.5	159.6	159.6	138	138	138				0.02	138.5	138.5
Qmin	0.19	0.1	0.38	0.25	0.41	0.29	0.2	0.4	0.3	0.2	2.5	0.26	0.14
Qmax	8.84	4.49	7.76	5.16	33.52	23.46	16.76	4	2.5	2.1		9.04	4.88
dmin	0.71	1.4	0.81	1.22	0.19	0.27	0.37					0.7	1.29
dmax	33.34	65.63	16.61	24.99	15.43	22.04	30.85					24.03	44.55
Comments	high flux		high resolution		highest Q-rangedisordered materials	standard wl	highest flux				low Q	very high flux

Single-crystal diffraction is a powerful method for the investigation of structural details in condensed matter. Hot neutrons are required to uncover the finest details in the nuclear positions and neutron spin polarisation is a handle to separate mixed components (nuclear polarisation, magnetic and electronic scattering).

A characteristic of the four-circle diffractometers is the use of Eulerian cradles for orienting the sample crystals, with the detector moving in a horizontal plane. Normal-beam diffractometers have a mechanism for tilting the counter out of the horizontal plane, thus enabling the installation of heavy equipment for special crystal environments (cryostats, magnets, etc.).

These diffractometers can be used to find:

average atomic positions. From these we can learn how the atoms are bound together to form molecules, and how the molecules are stacked;
local atomic distributions. This gives information about the time averaged thermal motion or the local atomic disorder;
magnetic structures and magnetic moment distributions.

Structural data of this kind are required for a large number of systems, ranging from organic molecules to high temperature superconductors. Often studies are made as a function of temperature, pressure and magnetic field which may lead to important modifications of the crystal structure.

D3 polarised hot-neutron diffractometer
D9 hot neutrons
D10 4-circle & 3-axis
D23 2-axis spectrometer (CRG)

D23 Diffraction Magnetism and quantum materials,

The thermal neutron diffractometer D23 is devoted to single crystal measurements, either with unpolarised or polarised neutrons, in the incident wave length range 1–3 Å. It can support large sample environments (pressure cells, up to 30 kbar, high field cryomagnets, up to 15T, dilution fridges, ...) and is characterised by a high flux and a very good signal to noise ratio.

D10 Diffraction Magnetism and quantum materials, Chemistry of materials

D10+ is unique in being the only four-circle diffractometer with optional energy analysis as on three-axis spectrometers. It also possesses a unique four circle dilution cryostat for temperatures down to 0.1K, and offers high reciprocal-space resolution and low intrinsic background, to medium real-space resolution.

D9 Diffraction Magnetism and quantum materials, Chemistry of materials

D9 is used for precise and accurate measurements of Bragg intensities up to very high momentum transfer. The resolution allows routine recording of extended data sets for the detailed study of atomic disorder and atomic thermal motions. The short wavelength allows the study of compounds containing absorbing elements like Gd or Sm.

D3 Diffraction Magnetism and quantum materials, Chemistry of materials

D3 is a highly versatile diffractometer designed for magnetic structure analysis. It offers several setups:

a high-field setup for 1D polarimetry up to 10 Tesla;
a zero-field setup for spherical neutron polarimetry using CRYOPAD;
a non-polarized setup for experiments requiring both short wavelengths and high magnetic fields;
a "liquids setup" that uses polarized neutrons to separately measure (and subtract) spin-incoherent background.

	D3	D7			D9	D10		D23	LADI
λ (Å)In bold the optimum	from 0.42 to0.84	3.1	4.8	5.7	from 0.3 to0.85	1.26	2.36	from 1 to 3	2.3	5
2θ(deg)min, max	from 5 to 121	from 10 to 155			from 5 to 120	3	146	from 4 to 130		0.13
Qmax - Qmin(Å-1)	from 26.04 to 0.65	from 0.4 to 4	from 0.3 to 2.5	from 0.2 to 2.1	from 36.28 to 0.64	9.54	0.14	from 11.39 to 0.15	5
Comments	Polarised neutron diffraction & complex antiferromagnetic structures	Diffuse scattering, permanent polarization analysis			High resolution crystallography & magnetism of absorbing materials	Magnetic structures & diffraction with energy analysis		Magnetic structures & magnetic phase diagrams	Protein crystallography (Laue diffraction)