A New High Resolution Neutron Powder Diffractometer at the Brookhaven High Flux Beam Reactor

Abstract

A high resolution neutron powder diffractometer under construction at the Brookhaven HFBR is expected to be completed by mid-1991. The new machine will have a Ge (511) monochromator with a take-off angle of 120{degree} ({lambda} = 1.89{angstrom}) and 64 {sup 3}He counters in the detector bank. There will be interchangeable collimators before the monochromator allowing a choice of 5 or 11 ft horizontal divergence, and 10 cm-high, 5 ft collimators in front of the detectors. In the higher resolution mode, {Delta}d/d is expected to be about 6 {times} 10{sup {minus}4} at the resolution minimum. The diffractometer is generally similar to D2B at the Institut Laue- Langevin except for the monochromator. This will consist of a vertically focussing array of segments 3 {times} 1.27 cm in dimensions cut from stacks of 20 0.43 mm wafers that have been pressed and brazed together. Preliminary measurements indicate that a mosaic width of 0.1--0.15{degree} and a peak reflectivity of 25% can be achieved in this way. 22 refs., 2 figs., 1 tab.