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 Å 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:

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

Contacts:

• NG1 8m SANS Telephone, (301) 975-5401
• Derek Ho, (301) 975-6422, derek.ho@nist.gov
• John Barker, (301) 975-6732, john.barker@nist.gov
• Paul Butler, (301) 975-2028, butler@nist.gov