SESANS Reproducibility Working Group

The spin-echo SANS (SESANS) working group is a subgroup of the canSAS Reproducibility and Reliability Working Group.

Mission

Spin-echo small-angle neutron scattering (SESANS) is a variant of small-angle neutron scattering that uses the Larmor precession of polarised neutrons to study the structure of materials in real space and up to length scales of some ten micrometer.

The mission of this group is to achieve SESANS measurements that provide data on an absolute scale independent from the used instrument. They do this by discussing the development of standard calibration samples and considering issues of reproducibility between different instruments, ensuring that data are trustworthy, reliable, and comparable.

Members

• Wim Bouwman (TU Delft)
• Robert Dalgliesh (ISIS Neutron and Muon Source)
• Henrich Frielinghaus (Jülich Centre for Neutron Science, MLZ)
• Fankang Li (Oak Ridge National Laboratory)
• Andrew Parnell (The University of Sheffield)
• Steven Parnell (ISIS Neutron and Muon Source)
• Roger Pynn (Indiana University Bloomington)
• Gregory Smith (Chair, ISIS Neutron and Muon Source)

News and Status

• 25 January 2024: Discussion of current and future SESANS data formats.
• 16 June 2023: Discussion of recent reproducibility measurements and possible future events. Minutes
• 20 January 2023: Discussion of recent test measurements and data analysis. Minutes
• 13 September 2022: Working group introduced to canSAS members at canSAS-XII. Presentation
• 30 November 2021: Discussion of recent measurements of possible standard samples and plans for next test measurements. Minutes
• 22 March 2021: Inaugural meeting of the group. Minutes

SESANS Nomenclature

As a group, we recommend the following nomenclature for SESANS measurements to ensure consistency between instruments and the literature.

SESANS data are measured as a function of a parameter called the "spin-echo length". This is represented by the variable δ. We do not recommend a preferred unit, and the choice of unit (μm, nm, or Å) should be chosen to suit the natural length scale of the measurement.

SESANS data itself are referred to as the "normalized scattering correlation function". This is a normalization of the experimentally measured parameters, the polarization of the sample (P) and the polarization of the reference (P0). These are combined to give the recommended presentation of SESANS data, the natural logarithm of P/P0 divided by sample thickness (t) and the square of the neutron wavelength (λ²), for brevity ln(P/P0)/(t*λ²). These are the two current recommended normalizations, and dividing by them should give instrument and wavelength independent data. There is no recommended variable for the normalized scattering correlation function. We recommend using the unit (cm^-1 Å^-2) for this, using natural units for sample thickness and scattering cross section (cm) and for neutron wavelength (Å).

Data Repository

Data from possible standards can be shared on the working group's Zenodo community.

Data will be reviewed to ensure that they comply with current file standards (*.ses) before acceptance.

SESANS Instruments

• Larmor instrument at ISIS Neutron and Muon Source (UK) ISIS Larmor
• SESANS instrument at Reactor Institute Delft, TU Delft (The Netherlands) Research instruments SESANS
• SESANS at Oak Ridge National Lab (USA) SESANS 1-D Ultra Low Q Small Angle Neutron Scattering

Mailing List

The Working Group maintains a mailing list to provide updates on activities and relevant data. You can subscribe to this at the JiscMail mailing list sign up form.

Session Notes SAS2024 - Sun 2024-11-03

Topic: Cross-calibration

• Following round-robin reference samples have been used so far for SESANS at several sources (according to Wim Bouwman): Flexi-Por, Papyex. These measurements have also been compared to SANS/USANS results from the same samples.
• But: these kinds of samples have the disadvantage that they show artifacts when used for TOF-SESANS.
• Also, the presented reference data had differences in peak-minima of measured reverence samples at different sources. The reason for this difference still has to be identified.
• General consens: We need more sets of standard samples at all facilities

Notes from the discussion round:

• What is needed: New standard samples with shorter length scales of around 50nm (but such gratings are difficult to make)
• The question was raised if new round robin samples should be fabricated which can be handed from facility to facility. On the other hand, a good reference sample depends on each use-case - there is no perfect standard sample for several techniques/facilities. Instead, good existing standard samples (like the above mentioned and already measured Flexi-Por/Papyex) should be used.