Appl Phys A (2010) 99: 531–535 DOI 10.1007/s00339-010-5603-6 The high-resolution powder diffractometer at the high flux isotope reactor V.O. Garlea · B.C. Chakoumakos · S.A. Moore · G.B. Taylor · T. Chae · R.G. Maples · R.A. Riedel · G.W. Lynn · D.L. Selby Received: 6 April 2009 / Accepted: 24 February 2010 / Published online: 16 March 2010 © Springer-Verlag 2010 Abstract Neutron powder diffraction is increasingly recog- nized as one of the most powerful techniques for studying the structural and magnetic properties of advanced materi- als. Despite the growing demand to study an ever-increasing array of interesting materials, there is only a handful of neutron diffractometers available to serve the US neutron scattering community. This article describes the new high- resolution powder diffractometer that has recently been in- stalled at the High Flux Isotope Reactor in Oak Ridge. The instrument is designed to provide an optimum balance be- tween high neutron flux and high resolution. Due to its ver- satility the diffractometer can be employed for a large vari- ety of experiments, but it is particularly adapted for refine- ments of structures with large interplanar spacings as well as of complex magnetic structures. In addition to traditional crystal and magnetic structural refinements, studies of phase transitions, thermal expansion, texture analysis, and ab initio structure solution from powder data can be undertaken. 1 Introduction Neutron powder diffractometers installed at various neutron scattering facilities around the world stand out as the instru- ments most popular and widely used by experimentalists. With the growing complexity of materials comes the need for an improved understanding of their crystallographic and magnetic properties, and in this respect, neutron scattering V.O. Garlea ( ) · B.C. Chakoumakos · S.A. Moore · G.B. Taylor · T. Chae · R.G. Maples · R.A. Riedel · G.W. Lynn · D.L. Selby Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA e-mail: garleao@ornl.gov has proven an invaluable experimental tool. Technologically important materials amenable to study by neutron diffrac- tion include, but are not limited to, catalysts, ionic con- ductors, superconductors, alloys, ceramics, cements, colos- sal magnetoresistant perovskites, magnets, radioactive waste forms, zeolites and minerals. The HB-2A High-Resolution Neutron Powder Diffrac- tometer has recently been installed at the High Flux Isotope Reactor (HFIR) at Oak Ridge, and it began its commission- ing process in December 2008. A picture of the instrument is shown in Fig. 1. The HB-2A was designed as an upgraded version of the old HFIR’s powder diffractometer (HB4) that served the scientific community for a decade (1990–2000). Relocated to the HB-2 thermal beam tube, the powder dif- fractometer directly benefits from one of the highest steady- state neutron fluxes in the world, provided by the 85 MW HFIR research reactor. As such, it was redesigned to offer an optimal balance between intensity and resolution. This in- strument is expected to be a workhorse for crystal and mag- netic structural studies of powdered samples, particularly as a function of intensive conditions. This paper describes the main characteristics of the instrument and illustrates its cur- rent capabilities. 2 Instrument components The diffractometer is positioned at the HFIR’s largest beam tube (HB-2), which is situated radially relative to the reactor core. To reduce the high energy neutron component in the incident neutron flux, a liquid nitrogen cooled sapphire filter is installed upstream of the main shutter. The main shutter provides a means for turning the beam off for all the in- struments located at this beam tube. After passing through