NEW MULTIDETECTORS AND MONOCHROMATORS ON ILL NEUTRON POWDER DIFFRACTOMETERS P. Convert, P. Radaelli and A. Hewat, Insititut Laue-Langevin, BP 156X Grenoble Cedex 9, 38042 FRANCE

A large position sensitive detector using the micro-strip on glass substrate technology has finally been constructed for the new ILL D20 powder diffractometer, while the old D1A diffractometer has been upgraded with a 150^o multidetector. A new multi-wafer monochromator has been installed on the high resolution machine D2B.

Multidetectors and monochromators are very important in making the maximum use of the limited neutron flux even on the high flux ILL reactor. Certainly, improvements to these technologies are much more cost effective than the construction of new neutron sources.

The D20 detector subtends a solid angle comparable to that of the best time-of-flight machines, but the time-averaged flux on the sample is higher. This means that either very small powder samples (mg) can be studied, or that chemical kinetic experiments can be performed on time scales of ~seconds.

The 150^o multidector on D1A, combined with a new focussing mono-chromator, means that this instrument can continue to serve as a `work-horse' for high resolution Rietveld refinement. The new control and data treatment systems, using Silicon Graphics workstations, allow immediate analysis and visualisation of the results.

ILL has now refined the BNL multi-wafer monochromator technology, having constructed a special hot-press furnace for wafer fabrication. The first such monochromator, on the high resolution diffractometer D2B, focusses a 300 mm neutron beam onto a 50 mm sample, resulting in high intensity while maintaining the very regular line shape needed for Rietveld refinement. The new ILL monochromator allows different wavelengths to be selected (1Å, 1.6Å, 2.4Å, 6Å) from different [hhl] planes, something not possible with earlier multi-wafer designs.

Further details of these and other developements in neutron diffraction at ILL are to be found on http://www.ill.fr/dif/