Neutron diffraction is the application of scattering techniques in elastic mode, i.e. no energy exchange with the system being investigated, to determine parameters related to the atomic and/or magnetic structures of material and components. Most applications lie in the regime of condensed matter.
Diffraction using a hot spectrum neutron beam that has relevance for analysis of structures having a large reciprocal space area Q = sin(θ)/λ (where θ is the scattering angle and λ is the neutron wavelength), i.e. to study phenomena occurring at short range order 0.1 to 0.8 Å. Applications include:
- Short and intermediate range order (disordered materials) in liquids, amorphous and nano-structured materials. Typical scientific questions include the precise determination of hydrogen positions and -bonds in molecules and framework structures, or of other light elements, e.g. Li or O in corresponding ion conductors.
- Magnetic structure studies on very absorbent systems, such as the actinides and lanthanides (Gd, Eu, etc.)
- Pair-Distribution Function (PDF) analysis of nano-crystalline materials.
Instrument configurations include both powder diffraction and single crystal.
Powder diffraction covers the conventional range of applications in crystalline matter with periodicities in the range 0.8 to 10 Å using thermal neutrons. A specifically configured high intensity neutron powder diffraction instrument enables taking measurements at high-speeds (minutes to seconds), for near real-time stroboscopic investigations of changes introduced through external sample environments and\or chemical induced reactions. The instrument characteristics are medium resolution and are equipped with a neutron detector covering a large 2θ extent (preferably continuous) for the speed of measurement and capturing a diffraction pattern in one setting. Typical resolution is Δd/d > ~ 2 x 10-3 (i.e. 0.2%). The applications cover a vast range of materials that include metals, ceramics, superconducting materials, ionic conductors, energy storage materials and systems, catalyses, etc.
A hi-resolution powder diffractometer is similar to the HIPD but is specifically optimised for high resolution. Instruments are characterised by very high monochromator take-off angles, >> 90°, in conjunction with tight horizontal beam divergence (generally ≤10’) to render resolution Δd/dmin < ~ 1 x 10-3 (i.e. 0.1%). Applications are specifically aimed at high resolution crystalline and magnetic structure studies.
A neutron strain scanner is a specialised case of neutron powder diffraction where Bragg peak positions are measured spatially- and depth resolved in solid samples and components by exploiting the superior penetration of neutrons. The instrument is optimised for a 90⁰ scattering geometry and has medium resolution. From the interatomic spacings, strain and subsequently stresses are calculated. In addition such instruments can also be used to study crystallographic bulk or depth resolved texture (preferred orientation). Materials that can be investigated include all crystalline materials that are of technological interest to engineering.
Single-crystal diffraction is a non-destructive analytical technique which provides detailed information about the internal lattice of crystalline substances. This enables determination of unit cell dimensions, bond-lengths, bond-angles, and details of site-ordering. Neutrons are specifically well suited for the investigation of hydrogen bonding. Many of the most important functions in catalysis, pharmaceuticals and functional biology, depend on the hydrogen bonds and their characteristics. A 4-circle instrument uses monochromatic thermal neutrons in conjunction with elaborate sample orientation goniometers that can cover large sections of reciprocal space to systematically measure individual Laue spot positions and intensities using a single detector. Single crystals larger than 1 mm3 is required for this technique.
SCD-QL: Single Crystal Diffraction: Quasi Laue
The quasi Laue technique uses a white (broad spectrum) neutron beam and a large area cylindrical detector that surrounds the crystal to cover a very large area of reciprocal space. The advantage of this instrument is that substantially smaller single crystals can be studied, i.e. > 0.1 mm3.