Instrument description
The PITSI (Sesotho name for Zebra) instrument is located at the SAFARI-1 research reactor of the South African Nuclear Energy Corporation (Necsa) SOC Limited.
It enables medium resolution neutron powder diffraction capability for the study of crystallographic structures, chemical composition and magnetic properties in solid and powdered polycrystalline materials.
Neutron powder diffraction complements and extends the capabilities of conventional X-ray diffraction with regard to the following:
- Scattering off nuclei:
- Interaction strength atomic number independent: Sensitivity to light elements and their presence in heavy elements, distinguishing between neighboring elements in 3d, 4f and 5f bands, etc.
- Unlike X-ray diffraction, Neutron diffraction do not suffer form-factor fall off
- Magnetic interaction with unpaired electrons enables studies of magnetic phenomena
- Superior penetrating capabilities enables non-destructive in-situ parametric studies as function of temperature, pressure, magnetic field, chemical exchange of energy-storage materials such as Li batteries, etc.
Technical
Monochromator:
| Double focused bent perfect Si crystal |
| Wavelengths and take-off angle selections |
| Reflection: Si (331): Si (551): |
| 2θM = 70° 1.43Å 0.87Å |
| 2θM = 90° 1.76Å 1.07Å |
| Beam size: |
| Pseudo-2D detector: |
| Sample environments: |
| Sample mounting: |
| Flux at sample position: |
| Manually adjustable:5 – 15 mm horizontal5 – 48 mm vertical |
| 614 mm (hor. ) × 375 mm (ver.)Oscillating radial collimatorRange: 10° ≤ 2θ ≤ 130° |
| Top-loader vacuum furnace: 400 K < T < 1800 KBottom-loader cryostat: 4.5 K < T < 320 KTop-loader cryostat: 1.5 K ≤ T ≤ 800 |
| 4-Position sample changer |
| 106 neutrons cm-2s-1 |
Resolution
Resolution of the PITSI instrument measured from Al2O3 powder.
Project examples
In-situ phase transformation studies to identify and quantify chemical phase and structural parameters.
In-situ magnetic studies to characterise magnetic order, determine phase transitions temperatures, etc.
Chemical phase quantification (Rietveld technique) in multiphase oxides (6 phases in this case). The inset shows the equivalent XRD pattern. Specifically note the presence of high intensities in the small d region (large diffraction angles, up to 120°).
Quantification of retained austenite in heat-treated ferritic steel. The inset shows the equivalent XRD pattern where predominantly only the ferrite peaks are detected.
Data reduction and analysis:
Data reduction is primarily performed in-house using custom-developed software called ScanManipulator and is available online here: https://github.com/Deon-Marais/ScanManipulator
[D Marais, A.M. Venter and J Markgraaff, Data processing at The South African Nuclear Energy Corporation SOC Ltd (Necsa) neutron diffraction facility. Proceedings of SAIP2015. (2016) 198-203. (ISBN: 978-0-620-70714-5)]
Data can then be analysed using various products such as Topas (https://www.bruker.com/products/x-ray-diffraction-and-elemental-analysis/x-ray-diffraction/xrd-software/topas.html) , GSAS-2 (https://subversion.xray.aps.anl.gov/trac/pyGSAS) or Fullprof (https://www.ill.eu/sites/fullprof/php/programs.html)
Referencing the instrument in publications:
A.M. Venter, P.R. van Heerden, D. Marais, J.C. Raaths, Z.N. Sentsho, PITSI: The neutron powder diffractometer for transition in structure investigations at the SAFARI-1 research reactor, Physica B: Physics of Condensed Matter 551 (2018) 422-425. (http://dx.doi.org/10.1016/j.physb.2017.12.017)
Instrument scientist(s):
Apply for beam time:
Please download the beam time request form here and return to the instrument scientist.