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TOF principle - IN5

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Principle of the TOF spectrometer IN5

IN5 is a typical direct geometry neutron Time-of-flight (ToF) spectrometer. This high precision instrument is used to study low-energy transfer processes as a function of momentum transfer (e.g. quasi-elastic scattering in solids, liquids, molecular crystals and inelastic scattering, etc).
The animation below (HTML5) shows how measurements are performed :

  • the continuous polychromatic neutron flux from the neutron guide H16 is turned into a pulsed monochromatic beam by a set of 6 choppers.
  • the monochromatic neutron bursts are inelastically scattered by the sample, either a liquid, a powder or a single crystal.
  • the scattered neutrons are collected by a huge detectors array  covering 30 m2.
  • the time-of-flight analysis of incoming neutrons from each monochromatic burst results in a three dimensional spectrum x, y (detector position), t (time).

This gives access to the so-called dynamic structure factor, S(Q,ω), describing the structure and dynamics of the sample at atomic level.

IN5 principle (html - 795 )

Animation developed by Nicolas Grégoire (designer, Cinema4D), Francis Gorgé (Interface, Hype), Alain Filhol (project leader)
Version 0.97 - ©2009-2021 Institut Laue-Langevin, A. Filhol, Nicolas Grégoire and Francis Gorgé

Step-by-step comments about the animation

Neutron beam: The neutron beam from the cold neutron guide H16 is continuous and polychromatic (with a nearly Maxwellian distribution).

Pulsing chopper (P): Two counter-rotating disks creating polychromatic neutrons bursts.

Frame overlap chopper (FO) : A slowly rotating single chopper. It produces neutron burst with a reduced bandwith and well spaced to avoids the overlap of successive bursts once neutrons are scattered by the sample.

Contaminant order chopper (CO): A single chopper. The CO chopper reduces the bandwidth of pulses produced by the FO chopper. 

Monochromator choppers (M): A pair of counter-rotating disks chops a single wavelength (a narrow band = nearly monochromatic neutrons) from the bursts that have spread over the distance between the CO and M choppers.

Sample

  • Intensity: Shows the angular or Q-dependence of the scattered intensity.
  • Time-of-flight : Shows that for each detector pixel the time of arrival to the detector is directly related to the energy exchange between the sample and neutrons.
  • Complete analysis: Example of 3D spectrum recorded in time-of-flight. Here the spectrum from helium in the polycrystaline hexagonal phase.

History

2021 - Fully redesigned for a better image quality and error corrections (Nicolas Grégoire, Francis Gorgé, Jacques Ollivier, Alain Filhol)
2017 - Rewamping of the 2009 version (HTML5/Javascript/Mp4), Laurent Thion (Flash decompilation), Francis Gorgé (Hype and javascript), and Alain Filhol (project leader)
2009 - Numicom: Flash version but, again, never finished since the company went out of business before the end of the project.
2006 - Ameg: 1st animation but never finished since the quote was much too low.