THE MULTIPURPOSE DIFFRACTOMETER ROTAX AT ISIS
W. Kockelmann1,2 , M. Weißer3 , W. Schäfer1 and A. Kirfel1
1Mineralogisch-Petrologisches
Institut, Universität Bonn, D-53115 Bonn, Germany
2ISIS Facility,
Rutherford-Appleton Laboratory, Chilton, OX11 0QX, UK
3Mineralogisches Institut,
Universität Würzburg, D-97074 Würzburg, Germany
email: wak@isise.rl.ac.uk
Keywords: neutron
diffraction, powder diffraction, time-of-flight, magnetic
structures, texture analysis,
The Rotax instrument at the pulsed spallation source ISIS at the Rutherford Appleton Laboratory, United Kingdom, is designed for diffraction studies of crystal and magnetic structures, mainly using polycrystalline samples [1]. 50% of the beam time on ROTAX are available for a German programme [2] with informal application of beam time in order to facilitate short-time access to the neutron instrument.
The ROTAX diffractometer has considerable advantages due to its modular set-up, spacious sample area, flexibility of different detector configurations and miscellaneous sample environment equipment. Due to a wavelength spectrum from 0.5 to 5.2 A and linear detector units in forward and backscattering geometry, complete diffraction patterns covering a d-range from 0.2 to 50 A are accumulated from the very start of a measurement. High and nearly constant resolution in direct space (Dd/d=4×10-3 in backscattering) and in reciprocal space (Qmax=30 A-1) are the basis of high quality structure parameters. The flexible set-up makes the instrument particularly suited for magnetic structure investigations taking advantage of the considerable flux of neutron wavelengths up to 5.2 A and of the possibility to tune resolution and d-spacing range.
Performance tests using the data collected from standard samples Al2O3, TiO2, CeO2 and NiO served to assess precision and accuracy of structure parameters. For example, accuracy of lattice and positional parameters is better than 0.01% and 0.05%, respectively. A major aspect of the performance study was the optimisation of ROTAX experiments with respect to efficient beam time use. In addition to the performance test results examples of recent experiments performed on ROTAX are presented.
The instrument has also been used for texture
analysis [3]. The pulsed white-beam angle-dispersive technique
allows the measurement of pole figures in a fraction of time
required by constant-wavelength diffractometers.