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 Disadvantages
  • 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.
Neutrons map

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