Mission Statement

Versatile, fast read-out single-crystal/powder diffractometer probing materials in extreme environments. WAND² features a high efficient, high resolution 3He 2D position sensitive detector. It enables WAND² to map a large portion of reciprocal space for single crystals to investigate low dimensional phenomena or acquire powder diffractograms in short time to characterize phase transitions.

WAND² is operated in collaboration with the Japan Atomic Energy Research Institute under the US/Japan Cooperative Program on Neutron Scattering Research.

Instrument Description

The HFIR HB-2C WAND² instrument was designed to provide two specialized data-collection capabilities: (1) fast measurements of medium-resolution powder-diffraction patterns and (2) measurements of diffuse scattering in single crystals. For 2018, this instrument has been upgraded with a curved, two-dimensional 3He position-sensitive detector covering 120° of the scattering angle with the focal distance of 71 cm and +/- 7.5° vertical coverage. This enables measurements of single-crystal diffraction patterns in a short time over a wide range of the reciprocal space, making WAND² useful to search for fundamental magnetic propagation vectors or measurements of diffuse scattering in single crystals. WAND² is also a medium resolution powder diffractometer where the high flux allows fast data sampling for studies of kinetics in phase transitions. Additionally, it can be used for time-resolved experiments for structural transformations having short time constants or in stroboscopic mode for reversible processes. The WAND² detector (BNL120) is a seamless two-dimensional position sensitive 3He gas counter with 8*480*512 pixels. This detector has 0.4 mm subwire resolution, which yields an angular resolution of 0.03125° on WAND². The vertical focussing Ge monochromator provides high flux at the sample position which allows fast parametric measurements. The full range of HFIR’s sample environment can be used, including cryofurnaces (4–800 K), furnaces (to 1800 K), cryostats (to 0.06 K), and cryomagnets (to 7 T). The high flux at the sample position also allows high pressure experiments with clamp cells up to 6 GPa.

Applications

WAND² is ideal for the studies of time-resolved phenomena and diffuse scattering in single crystals. Research performed at WAND² includes studies of the growth of ferroelectric ice-XI, hole and charge ordering in colossal magnetoresistance materials, and magnetic structures and correlations in low-dimensional magnetic systems and other magnetic materials.

Specifications

Beam Spectrum:

Thermal

Monochromator:

Vertically focused hot pressed Ge

Monochromator angle:

2Θ M = 51.5°

Wavelength:

λ = 1.5 Å (Ge 113)

λ = 0.95 Å (Ge 115)

Scattering angles:

0° < 2Θ < 156°

Collimations

Oscillating collimator radial before the detector

Detector:

2-dimensional 3He curved PSD with ~2e 6 pixels; event mode capability

Resolution

0.4 mm spatial resolution (x and y)