22 Jul 2009



LET is a cold neutron multi-chopper spectrometer for the study of dynamics in condensed matter to understand the microscopic origin of material properties.


​​​​​​​​​Inside the LET detector tank



The study of dynamics in condensed matter with inelastic neutron scattering provides one of the most exacting tests of the understanding of the microscopic origin of the material properties, particularly when combined with powerful computer modelling techniques now being pioneered.

The ability to make quasi-elastic and inelastic measurements over a wide dynamic range from 0.5-30 meV on a single spectrometer is quite unique. Combined with position sensitive detectors covering scattering angles from 5° to 140°, LET is having a considerable impact in many disciplines including bio-materials, polymers, magnetism and quantum fluids.

Example applications

  • Quantum fluids
  • Magnetism
  • Polymers and bio-molecular materials


Recent proposal rounds have seen significant number of beamtime proposals rejected by the panel for similar reasons. The Excitations group and Facility Access Panel wish to help users to submit good proposals so would point out the following reoccurring issues of missing information in proposals that is detrimental to their scores, together with straightforward remedies:

  • Lack of evidence that a large single crystals exists or that a sufficient number of co-aligned crystals can be aligned for the experiment. This can be resolved by including a picture (with scale bars)
  • Lack or unclear presentation of relevant structural and physical property characterisation of the materials to be studied. This can be resolved by presenting diffraction and physical properties characterisation of your samples in the proposal.
  • Lack of details regarding what will be measured during the experiment which makes it challenging or in some cases impossible for the viability and merit of the proposal to be assessed during review. This can be resolved by proposers contacting ISIS staff prior to proposal submission.


LET uses a coupled cold Hydrogen moderator. Two sets of fast counter-rotating disc choppers are used to monochromate the incident beam.​

Polarized neutrons

LET now supports uniaxial (Z-only) polarisation analysis following the installation of a supermirror polariser and 3He spin filter analyser. Two key features of the polarised mode are full access to the LET detector, and rapid changeover between unpolarised and polarised modes (approx. 3 hours). Due to current limitations on 3He production polarised experiments are limited to a maximum of 5 days and must be discussed with the LET instrument scientists well in advance of proposal submission (not doing so risks the proposal being rejected on technical grounds). Currently only a standard orange cryostat and 'hot stick', covering the temperature range 1.6 - 500K, are available for use with the polarised mode.

Did you know?

LET uses the world's first 4 m long position-sensitive helium detectors.​

Instrument links: 

Contact information for the LET instrument

Location and contact information for the LET beamline

​01235 567126