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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.
Characteristics and Performance