Polarised SANS at ISIS: new capabilities in Mantid
20 May 2026
Mantid is used to visualise, manipulate and analyse neutron and muon scattering data. The team continue to increase its data reduction capabilities with the completion of their latest ‘Epics’ project on polarised Small-Angle Neutron Scattering (SANS). ‘Epics’ are coordinated development projects with close collaborations between scientists and developers to integrate new large-scale features and production-ready workflows into Mantid.
SANS enables the investigation of structures from nanometre to mesoscopic length scales within the bulk of a sample. Like many other techniques at ISIS, SANS research covers a wide range of applications across soft matter, biology, engineering materials and magnetism.
Why polarised SANS?
With polarised neutrons, by controlling and analysing the neutron spin before and after the sample, it becomes possible to separate structural (nuclear) and magnetic scattering contributions, and to resolve the orientation of magnetic correlations. This capability is essential for studies on magnetic nanoparticles, superconductors, spintronic materials, and exotic large-scale magnetic textures.
The ISIS instruments Zoom and Larmor now support time‑of‑flight (ToF) polarised SANS, including polarisation analysis. Mantid plays a central role in turning these complex raw measurements into scientifically meaningful data. The new data reduction for polarised data enables a streamlined and reliable calibration, correction and data reduction in absolute scattering units.
Correcting polarised SANS data.
Working with polarised neutrons requires careful calibration of the polarising elements such as supermirror polarisers, radio‑frequency spin flippers, and analyser devices including polarised ³He cells. The latter are placed in the neutron beam before and after the sample to either select, flip, or measure the polarisation state of the neutron beam. These devices are highly efficient, but not perfect. As a result, neutron spin states can “leak” into one another in the measurement process. To reliably extract magnetic and nuclear scattering signals, these imperfections must be corrected.
In a collaboration between Mantid developers and ISIS SANS instrument scientists, a set of new algorithms has been added to Mantid. The algorithms offer flexibility and control over the different aspects of processing data for calibration, reduction and management in the reduction of polarised SANS measurements. This involves:
- Calibration measurements to determine the efficiency of each polarising component prior to the actual experiment.
- Tracking the time‑ and wavelength‑dependent effects, particularly for the polarised ³He analysers, whose performance slowly changes during an experiment.
- Applying numerical corrections to the measured spin‑resolved intensities to account for the efficiency of the polarising elements before a standard SANS reduction step can be carried out.
- Saving data sets and additional metadata that adhere to a new format in the NXcanSAS convention, which was developed specifically to store neutron polarised data and the necessary additional data to facilitate further data analysis.
Since version 6.14 of Mantid, we offer full support for these integrated algorithms as part of the data reduction workflow of Mantid. If you are interested in using Mantid for polarised data reduction, you can find more information about the usage and reach of these algorithms by looking into our documentation pages. Additionally, Mantid developers always welcome any support query or suggestion, just reach us through our support email.
