REACTOR-BASED NEUTRON DIFFRACTION STUDIES IN EARTH MINERAL SCIENCE: TIME RESOLVED, NON-DESTRUCTIVE, LIGHT ELEMENT, EXTREME ENVIRONMENT, AND MORE

Neutron diffraction is a powerful technique complimentary to XRD, offering several unique advantages due to its non-destructive nature, high penetration for bulk measurement, sensitivity to light elements, capability for isotopic and adjacent elemental contrast, prone to atomic thermal vibrations, magnetic structure and phase transitions, and flexible extreme conditions. Reactor-based neutron source provides a stable source of neutrons, making them ideal for in situ measurements. The High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) hosts 6 diffractometers, each with distinct capabilities: WAND², POWDER, DEMAND, HIDRA, VERITAS, and IMAGINE. The HB-2C WAND² instrument is designed for both single-crystal and powder measurements.

WAND² was upgraded with a ³He 2D-PSD in 2018, offers two specialized data-collection capabilities: (1) rapid data acquisition of powder diffraction patterns, and (2) weak signals and diffuse scattering in single crystals. It’s large area detector and high-flux neutrons are key features, covering large reciprocal space for small single crystal to identify magnetic propagation vectors and to study diffuse scattering and weak signals. WAND² is also a medium-resolution powder diffractometer with rapid data sampling. This feature is particularly beneficial for parametric studies and monitoring kinetics in phase, highlighting a time resolution from msec to few mins, with each neutron event individually timestamped, and with experimental variables synchronized into metadata steam.

WAND² currently supports experiments in various sample environments, including cryostats/CCRs (to 50 mK), cryofurnaces (4–800 K), furnaces (to 1800 K), cryomagnets (to 6 T and 1.5 K), clamp cells (to 2.5 GPa), and PE cell (to 20 GPa at RT). Additional sample environments specifically tailored for Earth Mineral Science are available upon request through the instrument team, including electrochemical cell, flow-through reaction cell, gas adsorption, laser excitation, etc. Easy access to sample position allows the implementation of user supplied equipment. Looking forward, the planned HFIR Beryllium Reflector Replacement upgrade in 2028 will expand its capabilities by the installation of a new monochromator, which provides high resolution data acquisition and access to multiple wavelengths.