Overview
The Small Angle Neutron Diffractometer for Amorphous and Liquid Samples (SANDALS) is located on the north side of ISIS Target Station 1 and views the liquid methane moderator, making use of neutrons with wavelengths ranging from 0.05 – 4.95 Å. One set of B4C jaws and a B4C final beam scraper aperture are used to define the beam geometry, which most commonly has a 30 mm diameter circular cross-section. The 'small angle' part of the SANDALS name reflects the forward scattering arrangement of its 660 detectors, which cover 2θ = 3 – 38°. This angular range comprises of 18 banks of 20 × 1 × 2 cm (height × width × depth) ZnS scintillator detectors providing a 0.7 sr solid angle coverage with a 50% efficiency for 1 Å neutrons and 0.1% stability over the timescales of a typical experiment. This arrangement of detectors means SANDALS is optimised for looking at samples containing light elements such as hydrogen or lithium as the contribution to the data by inelastic neutron scattering is minimised.[1] As with GEM, to help minimise backgrounds, the beam collimation and sample space are under vacuum during data collection to prevent air scattering.
The delivered wavelength bandpass combined with the detector angle coverage result in a practical operating Q-range for SANDALS of 0.1 Å-1 ≤ Q ≤ 50 Å-1. This delivers sub-Angstrom distance resolution (~0.1 Å) for pair distribution studies of liquids and disordered materials out to a maximum length scale of ~30 Å.
Owing to the forward scattering arrangement of detectors with a maximum 2θ of 38°, resolution of Bragg features in the measured diffraction patterns is limited in comparison to a traditional crystallography instrument. SANDALS can achieve a resolution of 2% ΔQ/Q across most of its operating Q-range. Instrument backgrounds have been minimised to very low levels, which, together with the detector stability, mean SANDALS can reliably perform isotopic difference measurements at the few % difference level. Typical measurement times are between 6 and 8 hours for a hydrogen-containing sample and shorter for a deuterium or non-hydrogen containing sample.
[1] A. K. Soper, Inelasticity corrections for time-of-flight and fixed wavelength neutron diffraction experiments, Mol. Phys., 2009, 107, 1667-1684.
Science
The physics and chemistry of liquids is a relatively young science, hence SANDALS reputation was initially built on the investigation of fundamental systems, from liquid argon to pure water. To some extent, it still plays a role in the SANDALS programme. The investigation of the structure of fundamental liquids commonly present in chemical and biological processes (for example solvents), makes up over 20% of the science performed on SANDALS.
In recent years, over one-third of SANDALS science is now in the area of healthcare, being concerned with the interaction of drugs, bio-molecules (such as sugars or peptides) and bio-materials (for example bio-glasses for synthetic bone). More often than not, the role of water in these systems is a key part of the scientific investigation.
Similarly, the investigation of ionic liquids and their application as novel green solvents is an area that has developed on SANDALS since 2007. Increasing numbers of disordered materials researchers are moving away from the low real-space resolution provided by traditional small angle instruments to seek a detailed understanding of the diverse molecular bonding in these solvents. More recently studies of the emerging area of deep-eutectic solvents have also contributed to SANDALS environmental programme.
The study of hydrogen storage and battery materials is a key area on SANDALS, as many scientists turn away from classical crystalline materials to investigate the interesting properties that disordered and amorphous materials have to offer. Additionally, heterogeneous catalysis and synthesis of catalytic materials has been studied on SANDALS, making use of the ability to dose samples in situ and thus examine a catalytic reaction in its before and after states. A theme that cuts across the energy, environment and manufacturing areas is the study of homogenous catalysis in water, where new compounds have the potential to substitute water for traditional solvents as a medium for chemical reactions.
For more detailed examples, please take a look at the instrument's science highlights page.
Instrument Information
