The new high resolution ultra small-angle neutron scattering instrument atthe High Flux Reactor in Grenoble

In 1998, the combined Interferometer and Ultra Small Angle Neutron Scatteri ng (USANS) instrument S18 at the 58 MW High Flux Reactor at the Institute L aue-Langevin in Grenoble (France) started operation. The instrument has bee n upgraded to allow more advanced neutron optics experiments for fundamenta l, nuclear and condensed matter physics. The new supermirror guide along wi th the two channel cut silicon perfect crystals, configured as an advanced high resolution Bonse-Hart camera, provides optimal intensity conditions. A large range of wavelengths is accessible by variations of the Bragg angle and by using different reflecting planes of a properly cut silicon monochro mator block in combination with different channel-cut analyzer crystals. Th e fine adjustment analyzer system is achieved by an advanced piezo drive, w hich has an accuracy of 0.036 seconds of arc. The basic features of the USANS camera, which takes advantage of a new tail suppression method, and the results of various test measurements concernin g intensities, long term stability and the accessible wavelength range will be presented. A high resolution position sensitive detector can either be used to analyze beam profiles or to perform neutron radiography experiments .