Aurora—A high-resolution powder diffractometer installed on the IEA-R1 research reactor at IPEN-CNEN/SP

Abstract

A high-resolution powder diffractometer (HRPD) was installed on the IEA-R1 research reactor at IPEN-CNEN/SP, São Paulo, SP, Brazil. It is an extensive upgrade of the old IPEN-CNEN/SP multipurpose neutron diffractometer which used a single boron trifluoride (BF 3) detector and a flat mosaic single crystal copper monochromator. The main modifications introduced were the installation of a position sensitive detector (PSD) and a focusing silicon monochromator. Placed at a distance of 1600 mm from sample, the PSD spans an angular range of 20° of a diffraction pattern. An extensive powder diffraction pattern can be obtained by collecting data in contiguous 20° segments. The double-focusing perfect single crystal silicon monochromator, installed in a take-off angle of 84°, can be positioned to produce 4 different wavelengths, namely 1.111, 1.399, 1.667 and 2.191 Å (nominal values). Diffraction patterns, obtained with the instrument, have shown a quite good resolution. Curves full width at half maximum (FWHM) vs. scattering angle ( 2θ) have been measured with powdered alumina using three vanadium sample holders 1/8, 1/4 and 3/8 in. in diameter. Such curves give the resolution that can be expected from the instrument in an interval 2 θ from 5° to 130°. In comparison to the former instrument, the new diffractometer has much better resolution and is, per intensity point, ca. 600 times faster in data acquisition.