Wombat, the high intensity diffractometer in operation at the Australian Centre for Neutron Scattering

TL;DR

Wombat provides a flexible, high-throughput neutron diffraction platform that supports rapid powder diffraction as well as texture and single-crystal studies. The paper details the instrument layout, detector system, and a comprehensive data collection and reduction pipeline, including normalisation, efficiency correction, vertical integration, and gain re-refinement, together with resolution-function characterisation for multiple monochromators. It highlights in situ and in operando capabilities, examples of rapid data collection and hydrogenous-material studies, and the growth of a large user community, concluding with future upgrades such as a new in-house detector to be commissioned by 2028. The work underscores Wombat’s impact on materials science through high-speed measurements, multi-parameter experiments, and broad sample-environment flexibility.

Abstract

Wombat is the high intensity neutron diffractometer in operation at the Australian Centre for Neutron Scattering. While primarily used as a high-speed powder diffractometer, the high-performance area detector allows both texture characterisation and single-crystal measurements. The instrument can be configured over a large range of operational parameters, which are characterised in this contribution to aid experimental planning. Wombat is particularly optimised for the study of materials in situ and in operando using the wide range of sample environment available at the centre. Over 17 years of operation, Wombat has been used to explore a broad range of materials, including: novel hydrogen-storage materials, negative-thermal-expansion materials, cryogenic minerals, piezoelectrics, high performance battery anodes and cathodes, high strength alloys, multiferroics, superconductors and novel magnetic materials. This paper will highlight the capacity of the instrument, recent comprehensive characterisation measurements, and how the instrument has been utilised by our user community to date.

Figures (11)

• Figure 1: Schematics of the Wombat instrument. Both diagrams show the instrument configured with a take-off angle of 90$^{\circ}$, and a detector start angle of $\approx$ 14$^{\circ}$, which is the most common configuration of these components. The upper panel shows the 'walk in' view, displaying the relative height of the components, while the bottom panel gives a birds' eye view of the instrument layout with the beam path marked in purple. The scale marker is approximate
• Figure 2: $\Delta d/d$ resolution curves calculated from the peak shape functions fitted for the 113 reflection of the focusing Ge monochromator, 113 reflection of the flat Ge monochromator and 002 reflection for the focusing graphite monochromator across the range of take-off angles.
• Figure 3: Bar chart illustrating the use of different pieces of sample environment equipment on Wombat during user experiments. Multiple pieces of sample environment equipment may be used during a single experiment, which is why the total sample environment equipment uses charted (1222) exceeds the number of experiments (805) listed in Section \ref{['User_community']}.
• Figure 4: Neutron diffraction patterns collected in situ as reagents mixed for Na$_{0.7}$WO$_3$ are dropped into a preheated furnace, set to various temperatures. The colourmap limits are identical across (c–e) but are different from those in (a, b) due to the different acquisition conditions. These patterns are shown with the SiO$_2$ background subtracted. Reprinted with permission from tegg2021intermediate. Copyright 2021 American Chemical Society.
• Figure 5: Detector image from a recent data collection of C$_3$H$_8$ propane on Wombat, collected at $\lambda$ = 2.422 Å and processed using the gain refinement strategy explained in the text. This illustrates that despite the low symmetry ($P21/n$ space group) and high hydrogen content the Bragg peaks can be seen over the high incoherent background.