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Time of flight spectrometer

A set of pedagogical interactive animations demonstrating the behavior of some neutron spectrometers.

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Films and animations

Neutron Time-of-flight 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 or Flash ) 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.

A screen shot of the Flash animation interface.

Click HERE to launch the HTML5 animation (for computers, smartphones and tablets)
Click HERE to launch the Flash animation (Flash must be installed and unlocked)

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.

  • Contaminant order chopper (CO): A single chopper. It removes harmonics due to the large bandwidth after the P choppers from the incident beam. This is equivalent to reducing the bandwidth before the monochromator choppers. 
  • Frame overlap chopper (FO) : A single chopper. It avoids overlapping of scattered neutrons from successive bursts after sample by suppressing some of the produced pulses.

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


  • 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.


Offline HTML5 version (32.4 Mb):

  • This version is an HTML5 rewamping of the original animation by Numicom (2009)
  • It is now compatible with computers, smartphones and tablets.
  • Project leader: A. Filhol (ILL); Design: Numicom; Flash: Ecliptique; HTML5: Francis Gorgé

Original Flash version 14.4 Mb):

  • This version was developped by Numicom en 2009.
  • File download (14.4 Mb):

Page by A. Filhol <filhol(at)> and J. Ollivier <ollivier(at)>: 20 March 2011