A guide to new scientific opportunities on HRPD at the ISIS Facility

Richard M. Ibberson, ISIS

The on-going development of instrumentation at neutron facilities such as ISIS is crucial for optimal utilization of the source and to keep pace with the increasingly stringent demands of materials characterization in emerging fields in science and technology research. The high-resolution powder diffractometer, HRPD, at ISIS has been upgraded recently with the installation of a 100 m long high-reflectivity supermirror guide. Using modern optics concepts, such as ballistic and elliptical guides, coupled with advances in supermirror technology, the new guide has realized flux gains between 1 and 2 orders of magnitude compared with the original "day 1" guide installed on the instrument. The current design process benefits from extensive Monte Carlo simulations, which are used not only to verify the predictions of the theoretical models with more realistic components, but also to optimize some of the design parameters. At ISIS, we have implemented a grid-based Monte Carlo engine, which can produce Rietveld-refineable data from fully-realistic virtual instruments with complex primary-optics and detector geometries. Results of these simulations will be presented, together with the first real neutron data, for the upgraded HRPD. It will be shown that the flux gains from this unique curved elliptical guide are produced without significant loss of resolution or deterioration of the peak shapes in both simulations and real data. The new guide also transmits shorter wavelength neutrons that were previously cut off making it feasible to access even shorter d-spacings. Initial results collected during the recent technical and scientific commissioning programme will be presented demonstrating HRPD's improved performance. Opportunities for new science, using examples which compare new results with past highlights on HRPD in the field of molecular crystallography as well as more recent topical studies on hydrogen storage materials, will also be discussed.

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