Larmor

This instrument is commissioning .

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Larmod CAD image
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Multi-purpose instrument for SANS, diffraction and spectroscopy utilising the larmor precession of polarised neutrons. Larmor will provide a suite of techniques not currently possible at ISIS and will also expand the range of spatial and temporal length scales to new areas.

The Larmor instrument will implement a number of sophisticated and recently developed techniques based on the application and extension of the neutron spin-echo concept in a single instrument. This multi-purpose instrument for SANS, diffraction and spectroscopy relies on the Larmor precession of polarised neutrons and will be able to measure changes in materials ranging from 0.1 femtometres up to 20mm.

Five techniques will eventually be available on the instrument. In the first stage of development SESANS (Spin-Echo Small Angle Neutron Scattering) and Larmor diffraction will be available. In a later stage of development,  MIEZE (Modulated Intensity Experiment with Zero Effort) spectroscopy, MISANS (a hybrid instrument combining the MIEZE technique and conventional SANS) and NRSE (Neutron Resonant Spin-Echo) spectroscopy will be implemented.

All of these techniques, which rely on the precession of the neutron spin in a magnetic field, have sound theoretical groundings, have been experimentally demonstrated, and are applicable to pulsed neutron sources.

Larmor will find use in exploring the science of soft matter and complex fluids, food science, bio-materials and pharmacy, advanced materials engineering, environmental and earth science.

Spin-echo small-angle scattering uses the neutron spin as a method of precisely encoding the path of neutrons through the instrument while retaining a large and divergent beam. The spin manipulation allows the usual resolution of the instrument to be decoupled from the physical collimation extending the Q range towards that accessible using ultra-SANS techniques. The measured signal produces a real space density autocorrelation function allowing direct comparison with complementary results from conventional microscopy and imaging. Length scales from about 5 nm to over 20 µm can be probed. In comparison, conventional SANS measures in reciprocal space and becomes flux-limited at very low Q values due to long flight paths.

Many of the soft matter themes relevant to science today will be extended to significantly longer length scales by SESANS, retaining good count rates and the advantages of neutron contrast variation.  For larger particles the shape of the structure factor and long range correlations, are decoupled from the particle shape, allowing the nature of interactions and the local packing to be easily revealed. This technique allows detailed studies of long-range structure and inter-particle interactions in colloidal dispersions, foams and lamellar fragments with potential applications in areas such as photonics, drug delivery, gene therapy, catalysis, separation science, and next-generation materials.

Larmor diffraction applies precession encoding to wide angle diffraction allowing precise measurement of lattice parameters or measurement of mosaic spread. In conventional neutron diffraction, the resolution of the lattice parameters is strongly determined by the angular spread of various parts of the beam. Using Larmor precession of a polarised beam, lattice constant changes can can be measured with very high accuracy.

The Larmor instrument will offer polarised beams with analysis over a wavelength range from 0.5-13Å. A detector comprising 600x600mm 3He tube array with 8x8mm pixel size will be mounted at the end of a rotating detector bench on the secondary flight path. The spin-echo system will be developed as part of the very successful collaboration between ISIS and TU Delft. Glass polarising mirrors and 3He polarised gas wide-bandwidth filters are being developed.

Construction of the instrument has started and is expected to be completed in September 2014.

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