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Materials Probe For Internal Strain Investigations (MPISI)

Instrumentation Description

The Materials Probe for Internal Strain Investigations (MPISI – Zulu name for the spotted hyena) material science neutron diffraction instrument is located at the SAFARI-1 research reactor of the South African Nuclear Energy Corporation (Necsa) SOC Limited. It is optimized for non-destructive depth-resolved studies of internal strain in bulk structures originating from manufacturing processes and in-service loads. By exploiting the superior penetrating capabilities of neutrons MPISI provides a valuable analysis technique for cutting-edge research in materials engineering and related scientific disciplines. The instrument configuration also allows for the investigation of crystallographic texture in engineered materials and natural geological samples.

Typical investigations include:

  • Welded steel plates (up to 30 mm in thickness) and pipes (350 mm OD and 30 mm WT)
  • Aluminium ring and plug specimen with 50 mm diameter,
  • Additive manufactured titanium, Co-Cr-Mo and steel specimens,
  • High-resolution investigations, i.e. depth resolution and near surface stresses,
    • Laser shock peened aluminium plates 3.3 mm in thickness,
    • Laser welded and shock peened aluminium plates 3.3 mm in thickness,
    • Laser treated steels.
    • Large aluminium billets of dimensions 90 × 400 × 330 mm3

MPISI is designed to be on equal standing with similar instruments at leading international facilities. Advanced data acquisition, control and analyses systems enable measurement of complex multi-dimensional strain maps of samples whilst optimising neutron beam utilisation. By employing micro-stepping, in conjunction with surface scans, samples can be positioned to within 10 µm accuracy.

Technical MPISI is on equal standing with similar instruments at leading international facilities, follows ISO 21432:2019 (Standard test method for determining residual stresses by neutron diffraction) and prescribes to the Neutron Quality Label (NQL).


1. Neutron Diffraction Measurements Aluminium ring and plug specimen [GA Webster (ed.), “Neutron Diffraction Measurements of Residual Stress in a Shrink-fit Ring and Plug” 2000 VAMAS Report No. 38 ISSN 1016-2186]  

Hot rolled, followed by cold rolled, aluminium plate 3.3 mm in thickness: Correlation of stress results measured on MPISI (Necsa: investigated with a gauge volume of 0.6 x 15 x 0.6 mm3) and Kowari (Ansto, Bragg Institute, Australia: gauge volume of 0.2 x 15 x 0.2 mm3 )  

3. Depth-Resolved Residual Stress Determination Depth-resolved residual stress determination of Laser Shock Peen (LSP) treated aluminium alloy 7075-T651 samples (6 mm and 1.6 mm thickness) using complementary techniques. [S.N van Staden, C. Polese, D. Glaser, J.-P. Nobre, A.M. Venter, D. Marais, J. Okasinski, J.-S. Park. Measurement of Residual Stresses in Different Thicknesses of Laser Shock Peened Aluminium Alloy Samples. Materials Research Proceedings 4 (2018) 117-122 (]  

4. Residual Stresses by Neutron Diffraction ISO/TC 135/SC 5/WG 7: Modernisation of ISO/TS 21432 “Non-destructive testing – Standard test method for determining residual stresses by neutron diffraction”, for review as International Standard in 2016. Participation member of project team. Published as ISO 21432:2019.

5. Neutron Ecosystem for Sustainable Science Participating member of the BrightnESS² project entitled “Bringing Together a Neutron Ecosystem for Sustainable Science with ESS” which established a calibration protocol for all strain scanning instruments and definition of criteria for the Neutron Quality Label. R.S.Ramadhan, S.Cabeza, T.Pirling, S.Kabra, M.Hofmann, J.Rebelo Kornmeier, A.M.Venter and D.Marais.  Quantitative analysis and benchmarking of positional accuracies of neutron strain scanners.  Nuclear Instruments and Methods in Physics Research Section A 999 (2021)165230 ( Estimate of data acquisition times The graph gives an indication of data acquisition times required for the materials alpha-iron (mild steel), aluminium and titanium, to attain strain accuracies of 50 microstrain at gauge volume sizes indicated in the graph legend. Measurement times and gauge volume sizes are interdependent and governed by the strain resolution required. As a guide, when using a gauge volume of 5 x 5 x 5 mm3, up to 30 mm thick steel plates can be investigated non-destructively. Data reduction and analysis Data reduction is primarily performed in-house using custom-developed software called ScanManipulator and is available online: [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)]

Referencing the instrument in publications A.M. Venter, P.R. van Heerden, D. Marais, J.C. Raaths, MPISI: The neutron strain scanner materials probe for internal strain investigations at the SAFARI-1 research reactor, Physica B: Physics of Condensed Matter 551 (2018) 417-421. (

Instrument scientists Dr. Deon Marais, B.Eng Computer and Electronic; M.Eng & PhD Nuclear Engineering +27 (0) 12 305 5645 Prof. Andrew Michael Venter, PhD. Physics +27 (0) 12 305 5038

Apply for beam time Download the beam time request form, and submit it to the instrument scientists as well as the User Office at  

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