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8-m Small-Angle Neutron Scattering Instrument CHRNS Logo

The 8 meter SANS instrument on NG-1 is NO LONGER SUPPORTED in order to upgrade the instrument to a 10-meter SANS.

The 8-meter SANS instrument is located at the end of neutron guide NG-1 where the guide cross section is 50 mm x 50 mm. This is a moderate resolution instrument suitable for examining structural features in materials from roughly 1 to 100 nm.

The layout of the instrument is shown in the figure below. The beam from the guide passes through a liquid-nitrogen cooled filter consisting of 15 cm of polycrystalline beryllium and 20 cm of single-crystal bismuth to remove fast neutrons and core gamma rays, respectively, from the beam. Following the filter, a variable speed, variable pitch, mechanical velocity selector is used to tune the mean wavelength from 5 to 20 with a variable wavelength resolution (10 - 20% fwhm). The beam is collimated along a 4.5 m evacuated pre-sample flight tube with circular apertures at its entrance and exit.

The instrument has an evacuable sample chamber with a computer-controlled translation stage that accommodates multi-specimen sample changers with up to 5 sample positions. The sample chamber is removable, providing access to a 60 cm diameter rotatable sample table for large pieces of apparatus such as electromagnets and cryostats.

The post-sample evacuated flight path consists of three shielded cylindrical sections which are mounted on a frame that can be rotated about the sample position by about 7.5 to reach larger scattering angles. The section which houses the detector rolls along rails in the frame to allow the sample-to-detector distance to be changed from 3.6 m to 2.0 m. Built into the detector shield is an externally adjustable positioning device for locating a beam stop in front of the detector.

The detector is a multi-wire, 64 cm x 64 cm position-sensitive proportional counter with spatial resolution of 5 mm x 5 mm. The instrument is operated through a user-friendly menu-driven interface. Completed data sets can be reduced on-line. Both raw 2D data and reduced data can be transferred to CD's in ASCII format.

This instrument is being redesigned to become a 10-m SANS instrument with many of the features (insertable guides, motor-driven detector, large sample chamber, etc.) of the NCNR's 30-m SANS instruments.

Instrument Schematic:

top and side view of the 8-meter SANS instrument

Characteristics and Performance

  • Source: neutron guide (NG-1), cross section: 50 mm x 50 mm
  • Monochromator: mechanical velocity selector with variable speed and pitch
  • Wavelength Range: 0.5 to 2.0 nm
  • Wavelength Resolution: 10% to 20% (FWHM)
  • Source-to-Sample Distance: 4.5 m
  • Sample-to-Detector Distance: 2.2 or 3.8 m
  • Collimation: circular pinhole collimation
  • Sample Size: 5 to 25 mm diam
  • Q-range: 0.05 to 5.0 nm-1
  • Size Regime: 1 to 100 nm
  • Detector: 640mm x 640 mm 3He position-sensitive proportional counter (5 mm x 5 mm resolution)
  • Flux on Sample vs. Qmin
  •     Qmin(nm-1)    Is(n/cm2 - sec)
        0.05    1 x 104
        0.10    2 x 105
        0.15    1 x 106


Last modified 22-February-2005 by website owner: NCNR (attn: Jeff Krzywon)