MSE Seminar Series: Jose Rodriguez-Rivera, NIST/UMD
Friday, October 13, 2017
2110, Chemical and Nuclear Engineering Building
Speaker: Jose A. Rodriguez-Rivera, NIST Center for Neutron Research, UMD MSE
Title: 10 Years of Science with the Multi-Axis Crystal Spectrometer
The study of novel solid-state materials at the atomic scale is fundamental in efforts to model and understand their properties. Elucidating the interactions between atoms and molecules is central to the search for materials with higher temperature superconducting, greater information storage densities, and faster computers. Neutron spectroscopy is an essential and powerful technique with which to understand these interactions through measurements of the underlying atomic and magnetic order as well as the associated dynamics. An inherent constraint of neutron spectroscopy is that neutrons interact weakly with matter; this can result in low count rates, especially for small samples that are difficult to grow as single crystals. My research is based on the development, use and operation of the Multi-Axis Crystal Spectrometer (MACS), a world-leading neutron spectrometer with advanced capabilities that directly addresses this constraint. With the brightest cold neutron flux in the world (5.108 neutrons/cm2/s) and the 20-channel, low-background, high-efficiency detection system, the instrument allowed us to perform experiments that were not possible before. The instrument is particularly powerful for probing the wave vector dependence of inelastic neutron scattering in select ranges of energy transfer to access the dynamic structure of fluctuating systems. The heart of the instrument is a doubly focusing PG(002) monochromator subtending a solid angle of up to 5 mSr to the cold neutron source. The monochromating system includes radial collimators and a variable beam aperture to optimize Q-resolution, energy resolution, and flux on sample. The cryo-filter system for MACS II includes polycrystalline Be and filter grade pyrolytic graphite. The detector system consists of an array of 20 channels which combined subtend a solid angle of 0.2 Sr to the sample. Each detector channel is built around a vertically focusing doubly bouncing crystal analyzer for enhanced signal to noise. The detector channels feature a 90 minutes soller collimators and a cryo-filter exchanger system with Be, BeO and PG filters. On November 11th 2006 MACS produced its first Monochromatic neutron beam. The instrument was included in the NCNR user program in July 2009. Since then, more than 60 papers have been produced in high impact peer reviewed journals becoming the most productive cold neutron triple-axis spectrometer in the world. The talk will cover the development of the instrument and its experimental capabilities via some research examples.