A 100-position robotic sample changer for powder diffraction with low-background vacuum chamber

At the new Australian OPAL research reactor, experiments carried out at room temperature use a substantial fraction of beam time on the high-resolution powder diffractometer, Echidna. With an average data collection time of 2 h and a complicated safety interlock system to protect users, the need for a fully automated and remotely controlled system was quickly realized. This report presents a solution based on a commercial four-axis robot capable of loading samples from two 50-position sample trays, in any order, into an automatically evacuated chamber. This chamber significantly reduced background signal arising from air scattering, with the effect being especially pronounced at low and high 2θ angles. In the case of textured or inhomogeneous samples, the system may be re-configured so that the robot rotates the sample in the beam or translates it vertically through the beam.