/GISANS - Advancing data reduction and analysis Workshop

Workshop programme

Summary

Overall Summary

(i) ToF

• Instrument factors influence measurement strategies and tools are needed to aid this process.
• Background - effects of inelastic scattering can change background signals that would not be identified/recorded correctly with respect to wavelength by time-of-flight.
• Resolution is important regarding both wavelength and angle. The latter depends on collimation/beam divergence as well as footprint on the sample and spatial resolution of the detector. The footprint depends on angle of incidence. The footprint gives some spatial and angular resolution projected on the detector.

Full interpretation of data is likely to require extensive information to be available with processed data.

• Data reduction from raw data will require establishment of appropriate data formats for input to existing modelling and analysis software. The software may also need development to fully exploit the information that is available.
• ToF and mono mode have different data processing requirements!
  • Spread of wavelength in ToF = possible quasi elastic events vs. Mono = assumption of elastic scattering
  • this mostly impacts on Background: mostly inelastic

(ii) Multiple scattering

• Reflection and refraction (optical effects) should be distinguished from multiple scattering
• There is a need to agree on a common nomenclature
  • “Coherent multiple scattering” can refer to the situation in which successive scattering events are not treated independently but are combined quantum mechanically, i.e., the amplitudes from different scattering paths are added coherently. This use of "coherence" has to be distinguished from others such as simple spin-coherence widely discussed in neutron scattering.
  • Sub-cases of multiple coherent scattering: (i) propagation of the incident wave through stratified media, which is incorporated exactly in the optical formalism treating reflection and refraction; and (ii) scattering from embedded “particles” (additional scattering centers) which is treated as a perturbation within the 1st-order Born approximation. Both (i) and (ii) are within the quantum theory (‘coherent’).
  • “Incoherent multiple scattering” denotes an approximation in which scattering from each center is treated, but the subsequent propagation of scattered waves is represented within a semi-classical or ray-optical picture (Gaussian optics). This approach is conceptually analogous to the semi-classical treatment of transport phenomena based on the Boltzmann equation, where phase relations between successive scattering events are neglected. The result corresponds to summing intensities rather than amplitudes of scattered waves.

• There are several factors that influence multiple scattering: mean free path length & coherence length, sample size / geometry
  • They have to be identified before each experiment
• Multiple scattering is often present in background signals. It can be used also to explicitly enhance signal
• comparison of X-rays and neutrons:
  • X-rays: (mostly) strong absorption
  • Neutrons:
    • Absorption is often weak and therefore, scattering is relative to absorption, of higher intensity.
    • Hydrogen is a particularly strong incoherent scattering nucleus
  • Be careful when comparing the theory from GISAXS and GISANS!
• How to measure MS?
• For multiple scattering it can be useful to include Monte Carlo calculations such as McStas as tool for GISANS analysis.

• • • Example: ID10 ESRF

(iii) Background handling

• Background subtraction is dependent on:
  • sample system/geometry/the observable physics.
• Each system has to be treated in a different way.
• Useful recent work (F. A. Jung and C. M. Papadakis, 'Strategy to simulate and fit 2D grazing-incidence small-angle X-ray scattering patterns of nanostructured thin films' J. Appl. Cryst. (2023) 56, 1330–1347. https://doi.org/10.1107/S1600576723006520 ) regarding strategy to handle background for fits and simulations to GISAXS patterns.
• A survey would help to identify the necessary / common steps among the community for specific classified systems.

(iv) Normalization

• Full quantitative normalization procedure:
  • measuring GISANS together with NR & Off-specular scattering, to view the whole Q-space.
    • In NR: fit the data+background to the total signal (instead of subtracting!)
  • GIXOS?
• If this is not feasible:
  • Same as topic "Background": each system has to be classified for its way "how to be treated" - Survey needed! (Different normalization procedures at different beamlines and for different classes of systems)
• General aspects (sample independent):
  • Precise I(lambda) normalization of the beamlines has to be performed
  • Good to get a Survey "How is this done at different beamlines currently"?
  • Using AI?: Should then contain: (i) dataset that is similar to the experiments and (ii) what this data-set represents (physically)

• Data-reduction:
  • Insert corrections for efficiency etc.,
  • Uncertainty calculation reproducible?
    • Information on footprint, slits, .. (see detailed notes)
    • Further input to uncertainty apart from countrate?
• Comparison to SAS:
  • GISAS = normalization to DB vs. SAS: = calculation of differential cross section (not possible in GISAS)

(v) Using SANS software

• Regarding BornAgain:
  • Need a set of prototype models (check what is on the BA webpage) - especially for inexperienced users
    • This should include a very detailed description about its physical limitations, directly implemented into BA sending error messages if beyond range.
    • Can we benefit from models in other software packages?
    • SasView: easy user-insertions of new form-factors - learn from that?
    • Package approach in BA problematic?
  • Further good features to implement: (i) intensity w.r.t. direct beam, w.r.t multiple scattering background, w.r.t. general expected background (according to experience + commissioning).
  • How to get fitting for GISANS working?
• Inspiration from X-ray programs: Brookhaven, Ben Ocko, BornAgain. Other: BoToSim, BoToFit, SpinW

(vi) Instrumentation

• Missing

(vii) Common data format

• Pros and Cons of separating "reduction" and "analysis", i.e., having an instrument independent analysis without original raw information
  • Pro:
    • datasets are transferable between softwares
  • Con:
    • Throw away information?
    • Have to understand the inputs and what needs to be kept
    • How to calculate uncertainties?
• Why necessary to define in beginning: Once defined, file formats should not be altered, only extended (e.g. possible in nexus or cansas XML formats)
• Maybe not "throw away" raw counts after reduction, but keep all information? If suitable / manageable: Ask in Survey?

(ix) Magnetic Scattering

• considering ".nxs" files and dimensions: A scan of everything/motor should be considered a dimension in the "nxs". It should not be restricted to 4 dimensions.
• On-the-fly polarization analysis: online corrections are good. But highest precision correction should be done at the end of the experiment before the users go home.

(x) Off-Specular

• Missing

Outlook

• Letter in "Neutron News"
• Need a survey on : (i) Normalization, Background handling, Instrumentation and (ii) Data formats

Detailed Discussion session notes

POINT A. ToF-GISANS

• Presentation slides: To come
• Further Notes from the ILL-Workshop on: /ToF-GISANS

POINT B. Multiple scattering

• Presentation slides:

File:HF MuSc GISANS.pdf

• Further Notes from the ILL-Workshop on: /Multiple Scattering

POINT C. Background handling

• Presentation slides:

File:Background ideas.pdf

• Further Notes from the ILL-Workshop on: /Background handling

POINT D. Normalization

• Presentation slides:

File:GISANS-NormalizationDiscussionStarters.pdf

• Further Notes from the ILL-Workshop on: /Normalization

POINT E. Using SANS software

• No introduction talk
• Further Notes from the ILL-Workshop on: /Using SANS software

POINT F / Instrumentation & Q/lambda resolution

• Presentation slides:

File:2026 03 CANSAS Grenoble Resol Fn JFMoulin.pdf File:TopervergGISANS2026ILL1-part1.pdf File:TopervergGISANS2026ILL1-part2.pdf

• Further Notes from the ILL-Workshop on: /Instrumentation & Q/lambda resolution

POINT G. Need good documentation

• No Introduction talk
• Further Notes from the ILL-Workshop on: /Documentation

POINT H. Integration of McStas with BornAgain

• Presentation slides:

File:HF McStas.pdf

• Further Notes from the ILL-Workshop on: /McStas

POINT I. Get a common data format for GISANS data reduction:

• Presentation slides:

File:GISANS 2026 File Formats - Brian Maranville.pdf

• Further Notes from the ILL-Workshop on: /Common Data Format

POINT J. Computer simulations / AI support:

• No Introduction talk
• Further Notes from the ILL-Workshop on: /Computer simulations / AI support

POINT K. Off-specular scattering:

• Presentation slides:

File:Gutfreund OffSpec new part 1.pdf File:Gutfreund OffSpec new part 2.pdf

• Further Notes from the ILL-Workshop on: /Off-Specular Scattering

POINT L. Magnetic Scattering:

• Presentation slides:

File:Magnetic GISANS.pdf

• Further Notes from the ILL-Workshop on: /Notes Magnetic Scattering

POINT M. Data Reduction:

• Presentation slides:

File:2026 03 CANSAS Grenoble Data Reduction TOF JFMoulin.pdf File:2026 03 12 Monochromatic GISANS reduction v4.pdf

• Further Notes from the ILL-Workshop on: /Notes Data Reduction