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SANDALS
SANDALS is a total-scattering diffractometer geared towards measuring structure factors and pair distribution functions for disordered materials, including liquids, fluids, glasses and amorphous solids. It specialises in hydrogenous and light-element bearing materials, often making use of H/D isotopic differences.
Instrument scientists
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Technical information
| Key specs | SANDALS pre-2021 | SANDALS post-2021 front-end upgrade | SANDALS-II (planned) | SANDALS-II High-resolution detector bank (planned) |
|---|---|---|---|---|
| 2θ (°) | 3 – 38 | 3 – 38 | 3 – 41 | 57 – 123 |
| L2 (m) | 1.2 – 4.9 | 1.2 – 4.9 | 1.1 – 5.2 | 0.6 – 0.7 |
| Q (Å-1) | 0.1 – 82 | 0.1 – 82 | 0.1 – 88 | 1.2 – 221 |
| Ω (sr) | 0.282 | 0.282 | 0.666 | 1.14 |
| Max beam size (mm2) | 30 mm diameter circle | 30 x 30 square | 30 x 30 square | 30 x 30 square |
| Pixel size (cm2) | 1 x 20 | 1 x 20 | 1 x 20 | 0.3 x 19.2 |
| ε at 0.05 Å (%) | 11 | 11 | 18 | 3.4 |
| ε at 1.0 Å (%) | 85 | 85 | 91 | 51 |
| Flux (106 n cm-2 s-1) | 9 | 18 | 18 | 18 |
| Typical measurement time (min) | 360 | 142 | 49 | 32 in combination with main array |
| ΔQ/Q best (%) | 1.6 | 1.8 | 1.8 | 0.5 |
Related resources
Detailed instrument overview
SANDALS, the Small Angle Neutron Diffractometer for Liquid and Amorphous Samples, is 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.
Three sets of B4C jaws are used to define the beam geometry, which most commonly has a 30 x 30 mm2 square 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 0.3sr solid angle coverage with 85% 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]. 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 now between 3 and 4 hours for a hydrogen-containing sample and shorter for a deuterium or non-hydrogen containing sample.
Sample environment
Typical sample environments (non-exhaustive list):
- Flat plate sample changer, 15 samples, -15 to +90°C
- Cylindrical sample changer, 20 samples
- Oil bath superstick, -40 to +240°C
- CCR, 10 to 300 K
- Furnaces, up to 1600 K, or higher with non-V elements
- High-pressure fluids up to 0.5 GPa
- Gas panel
Recent publications
Instrument reference
All publications and datasets based on experiments using SANDALS should cite that the data is collected by DOI: 10.5286/isis.instrument.4860. Experiment DOIs follow the format 10.5286/ISIS.E.RBXXXXXXX, where XXXXXXX is the 7-digit experiment (RB) number and these can be viewed via the Data Gateway.
Reference publication: First Results from SANDALS – the Small Angle Neutron Diffractometer for Amorphous and Liquid Samples at ISIS, A Soper, ICANS-XI International Collaboration on Advanced Neutron Sources, 199O