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Excitations and Polarized Neutrons

Excitations Group 2016

Excitations and Polarized Neutron Group 2016
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We operate some of the world's leading neutron spectrometers, able to measure magnetic and atomic excitatons over a wide energy and momentum-transfer range. We also provide polarized 3He spin-filter cells across ISIS for use with polarized neutron scattering techniques.

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Inelastic neutron scattering can provide rich information about atomic motions and magnetic interactions. Neutrons are a weakly interacting probe that do not perturb the system under study, making the results directly comparable to theory.

Our science programme spans a wide range of areas from the investigation of model magnetic systems through to the dynamics of disordered materials and quantum fluids and the dynamics of hydrogen in chemical and biological systems.


The Instruments

All the instruments are direct geometry instruments where the incident neutron's energy is monochromated using one or more choppers.  Both LET and MERLIN can run in repetition-rate multiplication mode, where several incident neutron energies are used simultaneously.  

  MARIMAPSMERLINLET
Incident energy (Ei) [meV] 7-100025-20009-10000.5- 20
Energy resolution (% of Ei)
[meV]
low energy2-4%2-5%4-6%0.5-2.5%
high energy1.5%1.5%2% 
Q-range at ΔE=0  [Å-1]Min:0.036√Ei
Max:1.29√Ei0.7√Ei1.29√Ei1.32√Ei

MARI 

MARI has a wide angular coverage and a wide energy range and good resolution making it ideal for the study of phonon densities of states in crystalline and disordered systems, and crystal field excitations in magnetic materials.  MARI is the only chopper spectrometer at ISIS not to be equipped with a pixilated detector array using position sensitive detectors.  This makes MARI the instrument of choice for studies of polycrystalline and powdered samples, and liquids.  MARI also boasts the lowest instrumental background of the ISIS suite of chopper spectrometers, making the machine highly sensitive despite the relatively low incident neutron flux.  

MAPS

MAPS has a large array of position sensitive detectors at low angles making it ideal for the study of high energy excitations in single crystals.  A key feature of MAPS is its long secondary flight path (6m) which results in high energy resolution, a feature important for both single crystal magnetism and molecular spectroscopy experiments alike.  The high energy resolution of MAPS, and high energy transfer coverage at low Q makes the instrument ideal for complementary measurements of high energy excitations in molecular systems alongside TOSCA.

MERLIN

MERLIN is a high intensity, medium energy resolution spectrometer that would complement the high-resolution MAPS spectrometer.  MERLIN’s design exploits recent advances in technology with a m=3 supermirror guide to enhance flux, as well as 3 metre long position-sensitive detectors in a vacuum, making it ideal for the study of single crystals. The detector bank covers a massive π steradians of solid angle with an angular range from –45o to +135o in the horizontal plane, and ±30o in the vertical plane. This allows large swathes of Q,ω space to be accessed in a single run. MERLIN is able to run in repetition-rate multiplication (RRM) mode, allowing users to simultaneously measure with several incident energies.

LET

The LET spectrometer is the latest addition to the inelastic suite at ISIS and has been in the user programme since 2011.  It utilises the high flux of cold neutrons on TS2 for studying low energy excitations in the region from 10s of µeV up to around 25 meV.  LET employs repetition-rate multiplication (RRM) - utilizing the whole time frame by allowing many incident energies at once and analysing them all separately.  LET supports a wide range of energy resolutions and a large position sensitive detector array allowing studies of crystals or polycrystals and liquids. LET was also built with a non-magnetic environment and a larger sample flange to allow for extreme sample environment equipment including neutron polarisation

ALF

ALF is crystal alignment facility to make it possible to co-align multi-crystals, check the quality of crystals or simply pre-align a crystal prior to an experiment. You can request beam time on an application for beam time for any of the ISIS instruments. 


Magnetic Field Availability on the Instruments

There are three cryomagnets at ISIS used in high field experiment on the chopper spectrometers.  Each one provides a vertical field which is homogeneous over a large sample volume.  Each magnet may be used with a dilution or 3He insert for low temperature experiments.  The table below indicates what magnets are available on which instruments, and the maximum allowable field for each.

The 9T "Chopper" Magnet

This is a wide solid angle vertical cryomagnet commonly used on the LET spectrometer.  It affords an 80° opening in the horizontal plane with a ±15° vertical coverage.  There are no aluminium rings in this magnet, thus greatly minimising the background scattering.

The 14T Diffraction Magnet

This has been successfully used on LET for experiments which require fields > 9T.  While almost the full horizontal scattering plane is viewable with this magnet, the out-of-place coverage is limited to ±7°

The 7.5T Magnet

This is very occasionally used  - it has been used before on MAPS and MERLIN.  Aluminium tails are available for spectroscopy experiments.  The scattering angle coverage of this magnet is very limited, with a vertical coverage of ± 6°.  

 MARIMAPSMERLINLET
7.5 Tnot available< 1.5 T < 4 Tuntested
9 Tnot availablenot available < 2 T < 9 T
14 Tnot availablenot availableuntested < 13.5 T
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