PROGRESS IN SMALL-ANGLE NEUTRON SCATTERING AT THE INSTITUT LAUE LANGEVIN Roland P. May, Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 09, France

The new high-performance small-angle scattering facility D22 of the ILL went in operation in April 1995. After a shutdown for improving its detector performance, normal user operation was planned again from spring 1996 on.

Small-Angle Neutron Scattering (SANS) is a well-established technique at the ILL. The instrument D11 has been a world-wide reference for all other facilities of its kind since its commissioning in 1972. During the recent long shutdown of the ILL for a reactor repair, D11 was modernized and improved. The high demand for beam time, and the advent of new sample environment techniques (real-time and shear experiments etc.) motivated the plans for building a new facility, D22. ILL's second SANS instrument, D17, is being turned into a dedicated reflectometer.

D22 takes advantage of the high brilliance of the guide H512 (cross section 40 x 55 mm) pointing at the horizontal cold source. The 96 x 96 cm multidetector moves along a vacuum tube of 2.54 m diameter and 20 m length and can be laterally moved and rotated around its vertical axis. One detector setting can provide a qmax/qmin ratio of up to 50. A 25 cm long velocity selector by Dornier of 94 % peak transmission, rotating at a maximal speed of 28300 rpm, produces wavelength bands between 3 and 40 Å with a spread of 8 to 20% (FWHM) of an unequalled flux at the sample (maximum > 1 x 108 cm-2 s-1).

The improved features of D11 and D22 have allowed us to perform new types of experiments, amongst them neutron interferometry, and to push the limits of feasibility further, thus opening the door for studying new systems.