High Resolution Powder Diffraction Studies at ESRF

â—‹Andy Fitch

At the ESRF we have been operating a high resolution powder diffraction beam line for the last ten years. In June 2002 the beam line was moved from its original bending magnet (BM16) to a dedicated undulator source (ID31), giving a large gain in the photon flux over the entire operational energy range of 5 - 60 keV. Recent enhancements include the installation of a robotic sample changer, so that as many as 50 capillary samples can be studied automatically, without intervention by the user, over the temperature range of 80 K -1225 K. In manual mode the range 3.5 K - 1800 K is routinely available.
The beam line is suited to a wide range of studies, particularly powder crystallography where the narrow peak widths maximise the amount of useful information in the diffraction profile. The high flux means that a diffraction pattern can be measured in a few minutes, for strongly-scattering samples, allowing high-resolution studies as a function of multiple temperatures and/or compositions. The high flux can be a problem however, with sensitive specimens, such as organic molecules, suffering radiation damage. Following the seminal work of Von Dreele, powder diffraction studies on proteins have proven feasible, and have been enthusiastically taken up at ESRF. The talk will give a brief overview of the beam line, illustrated by some examples exploiting its high flux and resolution capabilities.