Neutrons
To determine the positions and motions of atoms in condensed matter
Neutron Advantages- Wavelength comparable with interatomic spacings
- Kinetic energy comparable with that of atoms in a solid
- Penetrating ⇒ bulk properties are measured & sample can be contained
- Weak interaction with matter aids interpretation of scattering data
- Isotopic sensitivity allows contrast variation
- Neutron magnetic moment couples to B ⇒ neutron “sees” unpaired electron spins
- Neutron sources are weak => low signals, need for large samples etc
- Some elements (e.g. Cd, B, Gd) absorb strongly
- Kinematic restrictions (can’t access all energy & momentum transfers)
The figure below shows the time and length (energy and wavevector) scales of the various neutron-based techniques (Courtesy of Ken Andersen - ESS). You can use it to identify the techniques which will best match your needs and then consult the list below to choose the appropriate instruments.
- Neutron diffraction reveals structural information on the arrangement of atoms and magnetic moments in condensed matter.
- Small Angle Neutron Scattering (SANS) explores the mesostructures of liquids and solids on length scales ranging from 1 nanometre to about a micron.
- Neutron reflectometry gives information (depth-dependent composition) on the structure of thin films and surfaces which can be solid/solid, solid/liquid, liquid/liquid and liquid/air interfaces.
- Neutron spectroscopy (TOF, TAS, Spin-echo, Backscattering) probes the dynamics of magnetic moments, molecules and lattices over length scales ranging from a few angstroms to tens of nanometers, and over timescales from tens of picoseconds up to the microsecond.
- Neutron imaging is a non-destructive technique, highly complementary to X-ray imaging, that can see inside materials and examine processes therein.
Experiments at Large Scale Facilities are performed upon research proposal acceptance. Deadlines for proposal submission are normally 2-3 times per year, depending on the Facilities. Proposals are peer reviewed by expert panels, graded and accepted for beamtime allowance only if they meet cut-off criteria. Before writing a proposal, you must clearly identify the instrument(s) and the instrument requirements for your needs. Contact the instrument responsibles and discuss your experimen feasibility and all related technical issues.
Writing a proposal always specify:- Proposal Summary
- Aims of the experiments and background (scientific background)
- Experimental Methods (measurement strategy)
- Beamlines and Beamtime requested
- Results Expected
- References