canSAS - User contributions [en]

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:27:02Z

Apostolos Vagias: /* Summary */

[[File:GISANS Programme FINAL.jpg|thumb|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.
* 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* “Coherent multiple scattering” refers 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.
* Sub-cases of multiple coherent scattering: (i) the propagation of the incident wave through the stratified medium, which is incorporated _exactly_ in the formalism; and (ii) the scattering from embedded “particles” (additional scattering centers) which is treated perturbatively 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 quantum mechanically, 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.
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogen absorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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 (Jung and Papadakis, J. Appl. Cryst. (2023) 56, 1330–1347) regarding strategy to handle background for fits and simulations to GISAXS patterns.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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!)
** GISOXS?
* 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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:16:38Z

Apostolos Vagias: /* Summary */

[[File:GISANS Programme FINAL.jpg|thumb|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.
* 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogen absorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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 (Jung and Papadakis, J. Appl. Cryst. (2023) 56, 1330–1347) regarding strategy to handle background for fits and simulations to GISAXS patterns.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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!)
** GISOXS?
* 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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:11:52Z

Apostolos Vagias: /* Summary */

[[File:GISANS Programme FINAL.jpg|thumb|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.
* 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogen absorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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 (Jung and Papadakis, J. Appl. Cryst. (2023). 56, 1330–1347) regarding strategy to handle background for fits and simulations to GISAXS patterns.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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 substracting!)
** GISOXS?
* 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)
* 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 (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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:09:06Z

Apostolos Vagias:

[[File:GISANS Programme FINAL.jpg|thumb|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.
* 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogen absorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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 substracting!)
** GISOXS?
* 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)
* 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 (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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:06:16Z

Apostolos Vagias: /* Summary */

[[File:GISANS Programme FINAL.jpg|thumb|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.
* 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogenabsorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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 substracting!)
** GISOXS?
* 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)
* 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 (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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

/GISANS - Advancing data reduction and analysis Workshop

2026-04-08T22:02:04Z

Apostolos Vagias: /* Detailed Discussion session notes */

[[File:GISANS Programme FINAL.jpg|thumb|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.
* Resolution is important both as regards wavelength and angle. The latter depends on collimation as well as footprint on the sample and spatial resolution of 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 should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment
* MS gives extra background: can be used to explicitly enhance signal
* X-ray comparison:
** X-rays: (mostly) strong absorption
** Neutrons:
*** absorption is weak and therefore scattering is of higher intensity.
*** Hydrogenabsorption strong
** Be careful when comparing the theory from GISAXS and GISANS!
* How to measure MS?
** GIXOS (grazing incidence X-ray offspecular scattering)
*** Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** 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.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

(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 substracting!)
** GISOXS?
* 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)
* 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 (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 overgone.
*** 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 seperating "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|thumb]]
* Further Notes from the ILL-Workshop on: [[/Multiple Scattering]]

'''POINT C. Background handling''' 
* Presentation slides:
[[File:Background ideas.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Background handling]]

'''POINT D. Normalization''' 
* Presentation slides:
[[File:GISANS-NormalizationDiscussionStarters.pdf|thumb|Introduction to Normalization - Sebastian Jaksch]]
* 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|thumb|Introduction to ToF Resolution aspects - Jean-Francois Moulin]]
[[File:TopervergGISANS2026ILL1-part1.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 1]]
[[File:TopervergGISANS2026ILL1-part2.pdf|thumb|Talk "DWBA: kinematics, coherence & resolution issues" from Boris Toperverg - Part 2]]
* 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|thumb|Introduction on McStas - Henrich Frielinghaus]]
* 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|thumb|Introduction on File Formats - Brian Maranville]]
* 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|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 1]]
[[File:Gutfreund OffSpec new part 2.pdf|thumb|Talk on "Offspecular Scattering" from Philipp Gutfreund - Part 2]]
* Further Notes from the ILL-Workshop on: [[/Off-Specular Scattering]]

'''POINT L. Magnetic Scattering:''' 
* Presentation slides:
[[File:Magnetic GISANS.pdf|thumb|Talk on "Magnetic and PA-GISANS" from Annika Stellhorn]]
* 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|thumb|Introduction to ToF Data Reduction - Jean-Francois Moulin]]
[[File:2026 03 12 Monochromatic GISANS reduction v4.pdf|thumb]]
* Further Notes from the ILL-Workshop on: [[/Notes Data Reduction]]

==== Organizational notes ====

File:2026 03 12 Monochromatic GISANS reduction v4.pdf

2026-04-08T22:01:33Z

Apostolos Vagias:

Koutsioumpas, Vagias, Gutfreund - Monochromatic GISANS reduction

/Normalization

2026-04-07T08:14:31Z

Apostolos Vagias:

Short summary from discussions/breakouts:
* Full quantitative normalization procedure:
** measuring GISANS together with NR & Off-specular scattering, to view the whole Q-space.
* If this is not feasible:
** Same as topic "Background": each system has to be classified for its way "how to be treated" - Survey needed!
* General aspects (sample independent):
** Precise I(lambda) normalization of the beamlines has to be performed

Notes:
* for normalization it should be taken into account hand-in-hand: Specular reflectivity measured and simulated via Parrat and Off-specular/GISANS measured and simulated via DWBA!
** Can NR help as a "reference" to normalize the GISANS measurement correctly - should it always go together?
** This is not possible for some of the existing beamlines where GISANS can be performed but NR not, especially for Monochromatic sources!
** At Tof-GISANS beamlines one could aim at getting the "NR" by measuring GISANS at different incident angles
* Another problem: we loose information on the background and on the correct normalization factor by the fact that we do not measure the whole real space anyhow, as the detector has finite size
* there are two different problems:
** a fully quantitative measurement and
** a reference to "1", where it would depend on the sample and the physics to be measured how to normalize (e.g., superconducting systems: with ref. via the T>Tc state, magnetic systems: with reference via the saturated state) BUT: this reference to "another sample state" is not for all systems possible. What then?
* Regarding the question "can magnetic references help" - this can not generally be done, as changing the layer system would impact on the sld, the background, the normalization, etc.
* Does the "correct normalization" only get critical if the background level is that high that changing the background in the simulation would change the simulated sld? Is that the same in NR and GISANS?
* What can you get from Q=0 in a GISANS measurement? Can one at all extract a quantitative solution from a GISANS measurement? Should rather we aim at always having proper reference systems that the cross section can be compared with for getting the physical parameters needed?

Notes group (?):
* Instrumental effects, one might need to worry about a few things. Normalisation in GI is very challenging. It would be nice for people to say what they have done but not sure what the best practise would be.
* Regarding data reduction:
** The approaches are not uniform if one is measuring the direct beam for normalisation monitoring. One has to put in corrections for efficiency etc. In SAS you are not concerned by normalising to the beam intensity but try to evaluate the differential scattering cross-section. This will be related to the amount of sample in the beam and is putting a constraint on models. If the sample is a sphere in a medium of something else one has to define the cross-section. In GI one can not identify the differential cross-section.

** Not obvious that in GISANS experiments everyone measures the incident beam intensity in the same way. A reference sample is very difficult and not the same as for SAS experiments. Many of the detectors will be damaged by the direct beam, at least it will not come linearly. One needs to know the WL distribution for the ToF instruments, the WL can be not the same as for the direct beam. This becomes something one has to define rather carefully. This is true for reflectometry as well.

** In the reduced file the raw counts are lost. People say the reduction should estimate the statistical uncertainty but it is not easy. The uncertainty for the measured intensity, one has to keep the footprint, are the slits reproducible? It can be one of the least precise things. 2 um on 20 um is 10% error. If one has very few counts it is a problem of statistics. One may have zeros in bins, one rebins to have 10-15 counts in bins… For GISANS there is not much beam. Along with the counts one needs to provide other sources of uncertainty. Sometimes people throw away a lot of information.

* Regarding NR comparison:
** In NR we can often get few counts and they turn zero after background subtraction, they datapoints disappear after taking a log. With few counts one can instead of subtracting the background fit the data+background to the total signal. One can measure background with the same poisson statistics. One has to measure with the same statistics and not just randomly subtract.

** Oversubtraction of background can drastically change the fitting result in NR. Understanding errors is complicated. Statistically correct way of doing things in terms of making a model, numerically it is unstable and has a lot of problems, fitting is tricky. Least squares is stable, other things are less so.

** The ultracontemporary methods, AI? This is a topic for tomorrow.
Provide training datasets have to be sufficiently similar to the experiment you are doing. To train you have to give not the dataset but also teach what it is representing.

******
******

/Background handling

2026-04-07T08:07:52Z

Apostolos Vagias:

Short overview from discussions/breakouts:
* Background subtraction is dependent on:
** sample system/geometry/the observable physics.
* Each system has to be treated in a different way.
* A survey will help identifying the necessary / common steps among the community for specific classified systems. Potentially very helpful input for GISANS from a recent paper (Jung and Papadakis, J. Appl. Cryst. (2023). 56, 1330–1347) regarding strategy to simulate and fit GISAXS patterns.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

Notes:
* How do you know which type of (multiple coh/incoh.) scattering exists? And then which model for background to use accordingly? Are there approximations?
* always use multiple terms of the DWBA approximation? Where to draw the boundary?
* should we aim at always including a ray tracing approach (like McStas) to consider multiple scattering effects? (see union components McStas): https://mads-bertelsen.github.io/tutorial/Union_tutorial_1_processes_and_materials.html
* this all would strongly affect fitting of GISANS - we guess that this is one reason that no fitting of GISANS exists at the moment?
* typical approach of subtracting background doesnt work if it comes from "the sample itself, i.e., by multiple scattering in the sample"
* can this be "tested" how much the sample affects the background, are there test samples for comparison?
* why not the "typical approach": you subtract the instrument background (has to be well known), and all other "background" has to be from the sample and has to be simulated/fitted? this has then to be known for all wavelength bands and incident angles
* comparison to QENS where signals are always weak - how is that handled? Can what is known from there be taken over? QENS: Start with approximations for the model, and this then has to be refined. Also there the precise knowledge of the sample and the estimations of multiple scattering involved have to be taken into account!
* measure multiple states / dispersions / other observables to decrease ratio (unkown parameters)/(measured parameters)
* how to judge if the simulation (even if fitting perfectly to the data) is the physical correct one? For the question of which parameters are influencing the cross section mostly using bayesian fitting: see papers from Josh (for reflectometry): https://journals.iucr.org/j/issues/2021/04/00/ge5096/ge5096sup1.pdf
* X-ray community:
** Very helpful the recent work (Jung and Papadakis, J. Appl. Cryst. (2023). 56, 1330–1347) regarding strategy to simulate and fit GISAXS patterns, potentially very helpful for GISANS.
** Grazing incidence background subtraction is very difficult already in the X-ray techniques. State of the art for X-ray techniques is looking for areas around the strong peaks. This solution is not optimal. You can’t put down the sample and so the best situation is to do the same experiment at a liquid-liquid interface with motion. Everything is in the same place, you put only the liquids in the same cell, GISAXS image with everything except the molecule which will be placed at the interface. Then make a new sample with the same position of the interface with an added molecule. The background sample has to be as close to the real sample as possible. = To have more information, not to be taken as the recipe for handling background.
** Surface scattering needs to be known to disentangle it from reflection.
* ToF aspects:
** Consider also ToF Background!
* How to acquire the Background:
** There is no general way to acquire data, many people do empirical background subtraction because there is no way to calculate it.
** Cut and put a polynomial under a peak without knowing what the polynomial is supposed to represent.

/ToF-GISANS

2026-04-07T07:58:13Z

Apostolos Vagias:

Time-of-Flight GISANS (near surface scattering) involves all of the issues that have been raised under other topics but some are of particular importance:

* Instrument factors influence measurement strategies and tools are needed to aid this process.

* Background - effects of inelastic scattering can change background.

* Resolution is important both as regards wavelength and angle. The latter depends on collimation as well as footprint on the sample and spatial resolution of 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.

These highlights drawn from summary discussion should be edited and extended after more input from breakout group discussion.

Detailed notes group (?):
* ToF and mono mode - different data processing requirements. You have a spread of wavelength (WL), an event mode dataset, whether it is quasi elastically scattered when it arrives on the detector. Mono instrument with no WL recording: making an assumption the signal is elastic. Elastic scattering is predominant but the background its often inelastic.

/Multiple Scattering

2026-04-07T07:50:04Z

Apostolos Vagias:

Short summary of discussions/breakouts:

* Reflection and refraction should be excluded from multiple scattering
* Need to agree on a common nomenclature
* Need to distinct between coherent multiple scattering (whether as propagation through stratified medium or scattering from different embedded particles) and incoherent multiple scattering
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment

Detailed:
* X-ray comparison (overlapping with topic Background):
** MS in the end gives extra background
** Some people use MS to enhance the signal explicitly. Or you make additional layer to enhance reflections
** Comparing X-ray and neutron background, X-rays behave nicer in terms of MS. When absorption is strong all the scattering is from near the surface. For neutrons the absorption is weak and therefore scattering is of higher intensity.
** Incoherent scattering cross section for hydrogen is very high and scattering attenuation of the beam penetration is limited. One has to be careful about comparing the theory for X-ray and neutrons.
** Diffuse scattering for X-rays at Liq-Liq interface is comparable to neutrons. The beam is below the horizon and there is an attenuated pattern seen.
** X-ray Software packages we can take inspiration from? Brookhaven, Ben Ocko, BornAgain

* Sub-cases of multiple coherent scattering and distinction from incoherent multiple scattering:
**In the framework of the distorted-wave Born approximation (DWBA), it is essential to distinguish between two distinct processes: (i) the propagation of the incident wave through the stratified medium, which is incorporated _exactly_ in the formalism; and (ii) the scattering from embedded “particles” (additional scattering centers) which is treated perturbatively within the 1st-order Born approximation.
Both (i) and (ii) are within the quantum theory (‘coherent’). Only in (i), each layer is represented by an effective static potential, simplifying the description of the background medium.

**The term “multiple scattering” refers 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.

**In contrast, “incoherent multiple scattering” denotes an approximation in which scattering from each center is treated quantum mechanically, 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.

* How to measure?
** GIXOS grazing incidence X-ray offspecular scattering. Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** When you move a liquid surface and wait for it to stop, the measurement duty cycle is poor (2 min vs seconds)
If you rotate the solid sample there is much less need to wait.
*** ID10 at the ESRF has a good setup. The same for BM26 with a tilted beam setup for solid-liquid interfaces. DCM beam tilting is used instead to avoid moving the sample.
*** Get inspiration from X-rays to improve the way we measure GISANS
*** Most productive groups are writing their own code and have their own ways to do experiments. Leading groups spend years analysing the data from an experiment. Writing their own code. Sharing is not common.

/Multiple Scattering

2026-04-07T07:44:45Z

Apostolos Vagias:

Short summary of discussions/breakouts:

* Reflection and refraction should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment

Detailed:
* X-ray comparison (overlapping with topic Background):
** MS in the end gives extra background
** Some people use MS to enhance the signal explicitly. Or you make additional layer to enhance reflections
** Comparing X-ray and neutron background, X-rays behave nicer in terms of MS. When absorption is strong all the scattering is from near the surface. For neutrons the absorption is weak and therefore scattering is of higher intensity.
** Incoherent scattering cross section for hydrogen is very high and scattering attenuation of the beam penetration is limited. One has to be careful about comparing the theory for X-ray and neutrons.
** Diffuse scattering for X-rays at Liq-Liq interface is comparable to neutrons. The beam is below the horizon and there is an attenuated pattern seen.
** X-ray Software packages we can take inspiration from? Brookhaven, Ben Ocko, BornAgain

* Sub-cases of multiple coherent scattering and distinction from incoherent multiple scattering:
**In the framework of the distorted-wave Born approximation (DWBA), it is essential to distinguish between two distinct processes: (i) the propagation of the incident wave through the stratified medium, which is incorporated _exactly_ in the formalism; and (ii) the scattering from embedded “particles” (additional scattering centers) which is treated perturbatively within the 1st-order Born approximation.
Both (i) and (ii) are within the quantum theory (‘coherent’). Only in (i), each layer is represented by an effective static potential, simplifying the description of the background medium.

**The term “multiple scattering” refers 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.

**In contrast, “incoherent multiple scattering” denotes an approximation in which scattering from each center is treated quantum mechanically, 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.

* How to measure?
** GIXOS grazing incidence X-ray offspecular scattering. Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** When you move a liquid surface and wait for it to stop, the measurement duty cycle is poor (2 min vs seconds)
If you rotate the solid sample there is much less need to wait.
*** ID10 at the ESRF has a good setup. DCM beam tilting is used instead to avoid moving the sample.
*** Get inspiration from X-rays to improve the way we measure GISANS
*** Most productive groups are writing their own code and have their own ways to do experiments. Leading groups spend years analysing the data from an experiment. Writing their own code. Sharing is not common.

/Multiple Scattering

2026-04-07T07:43:28Z

Apostolos Vagias:

Short summary of discussions/breakouts:

* Reflection and refraction should be excluded from multiple scattering
* Need to agree on a common nomenclature
* There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry
** They have to be identified before each experiment

Detailed:
* X-ray comparison (overlapping with topic Background):
** MS in the end gives extra background
** Some people use MS to enhance the signal explicitly. Or you make additional layer to enhance reflections
** Comparing X-ray and neutron background, X-rays behave nicer in terms of MS. When absorption is strong all the scattering is from near the surface. For neutrons the absorption is weak and therefore scattering is of higher intensity.
** Incoherent scattering cross section for hydrogen is very high and scattering attenuation of the beam penetration is limited. One has to be careful about comparing the theory for X-ray and neutrons.
** Diffuse scattering for X-rays at Liq-Liq interface is comparable to neutrons. The beam is below the horizon and there is an attenuated pattern seen.
** X-ray Software packages we can take inspiration from? Brookhaven, Ben Ocko, BornAgain

** Sub-cases of multiple coherent scattering and distinction from incoherent multiple scattering:
In the framework of the distorted-wave Born approximation (DWBA), it is essential to distinguish between two distinct processes: (i) the propagation of the incident wave through the stratified medium, which is incorporated _exactly_ in the formalism; and (ii) the scattering from embedded “particles” (additional scattering centers) which is treated perturbatively within the 1st-order Born approximation.
Both (i) and (ii) are within the quantum theory (‘coherent’). Only in (i), each layer is represented by an effective static potential, simplifying the description of the background medium.

The term “multiple scattering” refers 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.

In contrast, “incoherent multiple scattering” denotes an approximation in which scattering from each center is treated quantum mechanically, 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.

* How to measure?
** GIXOS grazing incidence X-ray offspecular scattering. Scattering from the object is modulated by the reflectivity, you can deduce reflectivity if you estimate the form factor.
*** When you move a liquid surface and wait for it to stop, the measurement duty cycle is poor (2 min vs seconds)
If you rotate the solid sample there is much less need to wait.
*** ID10 at the ESRF has a good setup. DCM beam tilting is used instead to avoid moving the sample.
*** Get inspiration from X-rays to improve the way we measure GISANS
*** Most productive groups are writing their own code and have their own ways to do experiments. Leading groups spend years analysing the data from an experiment. Writing their own code. Sharing is not common.

/Background handling

2026-03-19T16:22:13Z

Apostolos Vagias:

Ideas for discussion were introduced with the following slides:
[[File:Background ideas.pdf|thumb]]

Short overview from discussions/breakouts:
* Background subtraction is dependent on:
** sample system/geometry/the observable physics.
* Each system has to be treated in a different way.
* A survey will help identifying the necessary / common steps among the community for specific classified systems.
* In case of multiple scattering: Include McStas as standard for GISANS analysis?

Notes:
* How do you know which type of (multiple coh/incoh.) scattering exists? And then which model for background to use accordingly? Are there approximations?
* always use multiple terms of the DWBA approximation? Where to draw the boundary?
* should we aim at always including a ray tracing approach (like McStas) to consider multiple scattering effects? (see union components McStas): https://mads-bertelsen.github.io/tutorial/Union_tutorial_1_processes_and_materials.html
* this all would strongly affect fitting of GISANS - we guess that this is one reason that no fitting of GISANS exists at the moment?
* typical approach of subtracting background doesnt work if it comes from "the sample itself, i.e., by multiple scattering in the sample"
* can this be "tested" how much the sample affects the background, are there test samples for comparison?
* why not the "typical approach": you subtract the instrument background (has to be well known), and all other "background" has to be from the sample and has to be simulated/fitted? this has then to be known for all wavelength bands and incident angles
* comparison to QENS where signals are always weak - how is that handled? Can what is known from there be taken over? QENS: Start with approximations for the model, and this then has to be refined. Also there the precise knowledge of the sample and the estimations of multiple scattering involved have to be taken into account!
* measure multiple states / dispersions / other observables to decrease ratio (unkown parameters)/(measured parameters)
* how to judge if the simulation (even if fitting perfectly to the data) is the physical correct one? For the question of which parameters are influencing the cross section mostly using bayesian fitting: see papers from Josh (for reflectometry): https://journals.iucr.org/j/issues/2021/04/00/ge5096/ge5096sup1.pdf

/Notes Magnetic Scattering

2026-03-19T10:57:36Z

Apostolos Vagias: Created page with "* 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."

* 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.

Talk:/McStas

2026-03-19T10:55:25Z

Apostolos Vagias:

*Combination of McStas and BornAgain should be promoted. (very good for cases with doubts of instrument resolution, for example)
* You run neutron by neutron, no approximations.
* Not only for analyzing data, but also for planning the experiments

Talk:/McStas

2026-03-19T10:55:04Z

Apostolos Vagias: Created page with "*Combination of McStas and BornAgain should be promoted. (very good for cases with doubts of instrument resolution, for example) * You run neutron by neutron, no approximations. * Not only for analyzing data, but also for planing the experiments"

/Normalization

2026-03-19T09:43:06Z

Apostolos Vagias:

/Multiple Scattering

2026-03-19T08:02:51Z

Apostolos Vagias: Replaced content with "Short summary of discussions/breakouts: * Reflection and refraction should be excluded from multiple scattering * Need to agree on a common nomenclature * There are certain constraints for multiple scattering: mean free path length & coherence length, sample size / curvature / geometry ** They have to be identified before each experiment"

/Multiple Scattering

2026-03-18T17:23:30Z

Apostolos Vagias:

Group 1

Philipp:Distorted Wave Born Approximation, is some sort of multiple scattering, because incoming beam is split into reflected and refracted beams?

Joachim: reflection from interface can be described as scattering, in Sinha paper, they discuss scattering from infinite volume and then describe reflection. Known way to deal with reflection and refraction, this gives DWBA. Scattering is not by interfaces, they are taken into account by DWBA.

Henrich: Parratt algorithm is a dynamic approach. it takes into account multiple reflections. Do not know how it can get more precise.

'''reflection and refraction should be excluded from multiple scattering'''

If we calculate all transmission and reflection coefficients, we are left with 16 reflection and transmission combination terms. Some have different momentum transfers. this is shown like reflection/refraction, reflection/reflection. should we call this multiple scattering?

Ammar: Multiple scattering: Born approximation is single scattering event. Multiple scattering comes with further scatterign events, is not included in DWBA. magnetic interactions. when they are important, we cannot reply on Born approximation, but use multiple scattering in solid state. when first scattering event happens, system responds. this process continues. is a dynamical process, not single kinematical process.

'''Need to decouple between "Dynamic" term bing different than dynamic (meaning energy transfer)'''

Boris: full solution, we have to consider changes in the sample. even i first order scattering calculations,

Philipp (question to Boris): have you ever confused the term dynamic scattering with inelastic scattering?
Boris: with ToF is feasible. 100 neV (depends on wavelengths), to see this you need reasonable resolution in pulse. perfect for SNS, here at ILL we have rather broad pulse.

experiment from Sascha Frank on standing/moving waves. if it is standing waves, density gives periodic structure and same stripes. alternatively, if we have one magnon / phonon, we have one branch (stokes/antistokes). the excitations produce the harmonic.

Philipp: we consider higher orders of BA as multiple scattering?
Boris: Born series valid for amplitudes and valid within the transverse coherence lengths, that all interfaces produce one plane wave in same direction if we have lateral homogeneity and interfere with each other. but, multiple scattering when events occur in sequence but are incoherent in between of them. it could be multiple specular reflection, but gap should be greater than transverse coherence length (where particles reflect multiply within 1 cm gap). It may look like a semantic difference. You take interference between events or not? multiple scattering requires than path length is much greater than mean free path (1/Sigma_total*density of the particles).

'''Joachim: multiple scattering (in book of Sears) is treated in terms of transport theory.'''
need to have a distance to avoid interference

Philipp: higher order BA should not be called multiple scattering. would it make sense to call it coherence?
Boris: case of neutron guide (each reflection is quantum mechanic, superrmiror, each collision is not correlated with eachother), case of waveguide (there is resonance layer in between, it is expected with microbeam waveguide where they try to get from edge of the sample and nothing comes in, because it violates the coherence). isndie, they are all coherent from top to substrate, in substrate it goes trhough the edge.
if sample is smaller than coherence length,

Philipp:H'''enrich, do you calculate with matrix formalism reflection and transmission in each layer and you use them to calculate incoherent multiple scattering in each particle? so, this mode that calculates z-amplitude is calculated?'''
Henrich: '''this is what I want to do.'''
Boris: if you shoot through the dge and look through the other edge, is feasible. if thre is resonance layer in between, 10 microns layer and look through the edge maybe

Boris: forming microbeams using resonance layers as waveguide is OK, only when you come from the edge. only there, you will get enhancement from the other edge. Mean free path for neutrons is cm or few mm. for 1cm , I hav one particle only.

Henrich: '''can I have several scattering events independently?'''
Boris: '''if the distance is much greater than mean free path (1/N*Sigma_total, roughly few mm)'''

Philipp: multiple
Boris: particle, part goes in forward direction and (multiple scattering does not play a role in reflectivity)

incoherent sum of reflectivities.

Henrich: if you come with alpha_i> alpha_c, in the deptth, you can have independent events. if alpha_i< alpha_c, multiple scattering does not play a role.

Joachim: what is typical thickness of samples in conventional SANS?
Henrich: 1mm to 5mm (5mm stronger intensity. mean free path length that decides. total scattering cross-section that determines

Boris: '''for cold neutrons, mean free path ~few mm. but, cohereence length projection 100microns, the sample should be larger than that. we have 2 constraints (one from coherence length and one from mean free path length, both compared to sample dimension).'''

if sample is too long, will not prevent multiple scattering happening. as long as the coherence effects are averaged out, we can have

Boris: coherence length 0.1mm, sample size 1 cm laterally. That what we usually use to fit reflectivity, we have many thousands of these coherence spots, we averaged modulus square of reflectivity. incoherent sum of all coherence length (this is why it is proportional to projected areas on the beam). with very slow neutrons, this is possible, but nothing penetrates. example is whispering gallery. when there is multiple reflection from different mirrors circled around, one can turn direction of neutron (1cm radius and coherence length is 1mm) --> in such situation, multiple off-specular scattering. but this is curved surface

/Multiple Scattering

2026-03-18T16:48:13Z

Apostolos Vagias:

Group 1

Philipp:Distorted Wave Born Approximation, is some sort of multiple scattering, because incoming beam is split into reflected and refracted beams?

Joachim: reflection from interface can be described as scattering, in Sinha paper, they discuss scattering from infinite volume and then describe reflection. Known way to deal with reflection and refraction, this gives DWBA. Scattering is not by interfaces, they are taken into account by DWBA.

Henrich: Parratt algorithm is a dynamic approach. it takes into account multiple reflections. Do not know how it can get more precise.

'''reflection and refraction should be excluded from multiple scattering'''

If we calculate all transmission and reflection coefficients, we are left with 16 reflection and transmission combination terms. Some have different momentum transfers. this is shown like reflection/refraction, reflection/reflection. should we call this multiple scattering?

Ammat: Multiple scattering: Born approximation is single scattering event. Multiple scattering comes with further scatterign events, is not included in DWBA. magnetic interactions. when they are important, we cannot reply on Born approximation, but use multiple scattering in solid state. when first scattering event happens, system responds. this process continues. is a dynamical process, not single kinematical process.

'''Need to decouple between "Dynamic" term bing different than dynamic (meaning energy transfer)'''

Boris: full solution, we have to consider changes in the sample. even i first order scattering calculations,

Philipp (question to Boris): have you ever confused the term dynamic scattering with inelastic scattering?
Boris: with ToF is feasible. 100 neV (depends on wavelengths), to see this you need reasonable resolution in pulse. perfect for SNS, here at ILL we have rather broad pulse.

experiment from Sascha Frank on standing/moving waves. if it is standing waves, density gives periodic structure and same stripes. alternatively, if we have one magnon / phonon, we have one branch (stokes/antistokes). the excitations produce the harmonic.

Philipp: we consider higher orders of BA as multiple scattering?
Boris: Born series valid for amplitudes and valid within the transverse coherence lengths, that all interfaces produce one plane wave in same direction if we have lateral homogeneity and interfere with each other. but, multiple scattering when events occur in sequence but are incoherent in between of them. it could be multiple specular reflection, but gap should be greater than transverse coherence length (where particles reflect multiply within 1 cm gap). It may look like a semantic difference. You take interference between events or not? multiple scattering requires than path length is much greater than mean free path (1/Sigma_total*density of the particles).

'''Joachim: multiple scattering (in book of Sears) is treated in terms of transport theory.'''
need to have a distance to avoid interference

Philipp: higher order BA should not be called multiple scattering. would it make sense to call it coherence?
Boris: case of neutron guide (each reflection is quantum mechanic, superrmiror, each collision is not correlated with eachother), case of waveguide (there is resonance layer in between, it is expected with microbeam waveguide where they try to get from edge of the sample and nothing comes in, because it violates the coherence). isndie, they are all coherent from top to substrate, in substrate it goes trhough the edge.
if sample is smaller than coherence length,

Philipp:H'''enrich, do you calculate with matrix formalism reflection and transmission in each layer and you use them to calculate incoherent multiple scattering in each particle? so, this mode that calculates z-amplitude is calculated?'''
Henrich: '''this is what I want to do.'''
Boris: if you shoot through the dge and look through the other edge, is feasible. if thre is resonance layer in between, 10 microns layer and look through the edge maybe

Boris: forming microbeams using resonance layers as waveguide is OK, only when you come from the edge. only there, you will get enhancement from the other edge. Mean free path for neutrons is cm or few mm. for 1cm , I hav one particle only.

Henrich: '''can I have several scattering events independently?'''
Boris: '''if the distance is much greater than mean free path (1/N*Sigma_total, roughly few mm)'''

Philipp: multiple
Boris: particle, part goes in forward direction and (multiple scattering does not play a role in reflectivity)

incoherent sum of reflectivities.

Henrich: if you come with alpha_i> alpha_c, in the deptth, you can have independent events. if alpha_i< alpha_c, multiple scattering does not play a role.

Joachim: what is typical thickness of samples in conventional SANS?
Henrich: 1mm to 5mm (5mm stronger intensity. mean free path length that decides. total scattering cross-section that determines

Boris: '''for cold neutrons, mean free path ~few mm. but, cohereence length projection 100microns, the sample should be larger than that. we have 2 constraints (one from coherence length and one from mean free path length, both compared to sample dimension).'''

if sample is too long, will not prevent multiple scattering happening. as long as the coherence effects are averaged out, we can have

Boris: coherence length 0.1mm, sample size 1 cm laterally. That what we usually use to fit reflectivity, we have many thousands of these coherence spots, we averaged modulus square of reflectivity. incoherent sum of all coherence length (this is why it is proportional to projected areas on the beam). with very slow neutrons, this is possible, but nothing penetrates. example is whispering gallery. when there is multiple reflection from different mirrors circled around, one can turn direction of neutron (1cm radius and coherence length is 1mm) --> in such situation, multiple off-specular scattering. but this is curved surface

/Normalization

2026-03-18T16:22:02Z

Apostolos Vagias:

Notes:
* for normalization it should be taken into account hand-in-hand: Specular reflectivity measured and simulated via Parrat and Off-specular/GISANS measured and simulated via DWBA!
** Can NR help as a "reference" to normalize the GISANS measurement correctly - should it always go together?
** This is not possible for some of the existing beamlines where GISANS can be performed but NR not, especially for Monochromatic sources!
** At Tof-GISANS beamlines one could aim at getting the "NR" by measuring GISANS at different incident angles
* Another problem: we loose information on the background and on the correct normalization factor by the fact that we do not measure the whole real space anyhow, as the detector has finite size
* there are two different problems:
** a fully quantitative measurement and
** a reference to "1", where it would depend on the sample and the physics to be measured how to normalize (e.g., superconducting systems: with ref. via the T>Tc state, magnetic systems: with reference via the saturated state) BUT: this reference to "another sample state" is not for all systems possible. What then?
* Regarding the question "can magnetic references help" - this can not generally be done, as changing the layer system would impact on the sld, the background, the normalization, etc.
* Does the "correct normalization" only get critical if the background level is that high that changing the background in the simulation would change the simulated sld? Is that the same in NR and GISANS?
* What can you get from Q=0 in a GISANS measurement? Can one at all extract a quantitave solution from a GISANS measurement? Should rather we aim at always having proper reference systems that the cross section can be compared with for getting the physical parameters needed?

******
******

Henrich

Normalization
'''For normalization, important to know the footprint through reflectivity measurements'''.

Footprint correction (in reflectivity mode) should be best done before we do normalization

Si samples with known material, known SLD--> would that help? To have comparable geometry to work at all?
100nm etched 100 A wide roofs in Si and backfilled with Fe, to calculate expected intensity and calculate SLD that you have in the sample.

We do nano-etching with electron beam welding on the surface. Stripes should be fine, but we need to define orientation measurement, so it would be easier.

JF: Truncated rods can be difficult , because by subtle variations of angle, the scattering pattern changes drastically.

SJ: need to find out what can be done with chemical etching and electron beam etching. Have 1cm - 2 cm in all dimensions. If you work with microsample (square mm), footprint is way larger than whatever you have.

Reference sample should have same dimensions as real sample.

JK: Even if you have the reference samples, how do they help get the correct intensity?

PG: you double-check your data reduction, you check your calibration (features at same q-values), are absolute intensities at the same value?, to know how reproducible are. It is more for reproducibility.

PG: '''Normalization to direct beam, for GISANS we want to underilluminate (otherwise, we get lots of background)'''

JF: You measure difference in the film with contrast. If you do not know your footprint, you will not know your incident angle and the wavelength to the extend you want.

PG: All measurements we did with GISANS (large sample and small sample slits) we ensured underillumination.

PG: FIGARO --> ToF-GISANS was not easy.

SJ: More and more certain that we probably need one additional measurement:
- One reference sample
- One additional measurement with low intensity where we confine the beam very small, where footpirnt calculation becomes easier that we can use later to calibrate the measurement where maybe we can overilluminate
(JF: not sure if this will work. In your measurement where you overilluminate, e.g. resolution not that good, you measure GISANS over different depths.You do very different experiments. Might be useful but not simple scaling.)

SJ: for the moment, only simplistic approach. Without additional reflectometry, very hard to go to quantitative measurements.

AK: '''The approach of using the monitor will work, with sample big enough not to have overillumination problems'''.
PG: if it works, having GISANS with absolute intensity will be very valuable. The size of nanoparticle will define GISANS intensity.

PG: '''discussion about off-specular and cases where it influences direct beam and specular beam.'''
AK: you have troubles understanding where you define specular beam on the detector.

SJ: Reflectometry, we normalize to intensity of incident beam. We do specular reflectivity curve. Everything in plane is correlated, and everything not landing on specular beam is not collected.

PG: in case that you have such strong off-specular scattering, that you influence specular intensity. Boris has published couple of papers that he proposes to deal with this problem.

JK: To get all this info, you need to simultaneously fit spec reflectivity with off-spec and GISANS and

Simultaneously: exact same beam and sample,

'''Footprint correction (geometric considerations for absolute intensity)'''

/Background handling

2026-03-18T15:54:26Z

Apostolos Vagias:

Notes:
* How do you know which type of (multiple coh/incoh.) scattering exists? And then which model for background to use accordingly? Are there approximations?
* always use multiple terms of the DWBA approximation? Where to draw the boundary?
* should we aim at always including a ray tracing approach (like McStas) to consider multiple scattering effects? (see union components McStas): https://mads-bertelsen.github.io/tutorial/Union_tutorial_1_processes_and_materials.html
* this all would strongly affect fitting of GISANS - we guess that this is one reason that no fitting of GISANS exists at the moment?
* typical approach of subtracting background doesnt work if it comes from "the sample itself, i.e., by multiple scattering in the sample"
* can this be "tested" how much the sample affects the background, are there test samples for comparison?
* why not the "typical approach": you subtract the instrument background (has to be well known), and all other "background" has to be from the sample and has to be simulated/fitted? this has then to be known for all wavelength bands and incident angles
* comparison to QENS where signals are always weak - how is that handled? Can what is known from there be taken over? QENS: Start with approximations for the model, and this then has to be refined. Also there the precise knowledge of the sample and the estimations of multiple scattering involved have to be taken into account!
* measure multiple states / dispersions / other observables to decrease ratio (unkown parameters)/(measured parameters)
* how to judge if the simulation (even if fitting perfectly to the data) is the physical correct one? For the question of which parameters are influencing the cross section mostly using bayesian fitting: see papers from Josh (for reflectometry): https://journals.iucr.org/j/issues/2021/04/00/ge5096/ge5096sup1.pdf

*****
group 1

Notes:
Alexandros: going to a corner and measuring bkg

Philipp: this corner you go is below/or above the horizon?
Alexandros: below.

Philipp: below the horizon, you have negative intensities. the corner will be different below or above the horizon.

Alexandros: yes, because you have something that absorbs and scatters at the same time.

Philipp: better to take it below the horizon instrument background.

Alexandros: problem we had usually with bare substrate, we had no other way to estimate bkg.

JF: the incoherent signal you get is not as constant in angle as you expect.

SJ: in GISANS, closer to footprint, after 2 cm is all incoherent.
JF: and inelastic
SJ: instruments masuring reflectometry and GISANS, first you scan through angle (and identify critical edge).
then, use this approach to get average SLD of the sample. problem with this approach would be that no SANS instrument can use this approach. put sample in, first reflectometry (get SLD) and afterwards then GISANS.

intensity and wavelength

Henrich: a SANS machine can do everything a reflectometry machine can do.
Philipp: can cover some angular range to see total reflection.

JF: Yes, but with poor resolution, for subtle variations of SLD this maybe not possible. we try to measure reflectivity curves when we do GISANS measurements.

SJ: is always worth it.

/Normalization

2026-03-18T15:47:43Z

Apostolos Vagias:

Notes:
* for normalization it should be taken into account hand-in-hand: Specular reflectivity measured and simulated via Parrat and Off-specular/GISANS measured and simulated via DWBA!
** Can NR help as a "reference" to normalize the GISANS measurement correctly - should it always go together?
** This is not possible for some of the existing beamlines where GISANS can be performed but NR not, especially for Monochromatic sources!
** At Tof-GISANS beamlines one could aim at getting the "NR" by measuring GISANS at different incident angles
* Another problem: we loose information on the background and on the correct normalization factor by the fact that we do not measure the whole real space anyhow, as the detector has finite size
* there are two different problems:
** a fully quantitative measurement and
** a reference to "1", where it would depend on the sample and the physics to be measured how to normalize (e.g., superconducting systems: with ref. via the T>Tc state, magnetic systems: with reference via the saturated state) BUT: this reference to "another sample state" is not for all systems possible. What then?
* Regarding the question "can magnetic references help" - this can not generally be done, as changing the layer system would impact on the sld, the background, the normalization, etc.
* Does the "correct normalization" only get critical if the background level is that high that changing the background in the simulation would change the simulated sld? Is that the same in NR and GISANS?
* What can you get from Q=0 in a GISANS measurement? Can one at all extract a quantitave solution from a GISANS measurement? Should rather we aim at always having proper reference systems that the cross section can be compared with for getting the physical parameters needed?

******
******

Henrich

Normalization
For normalization, important to know the footprint through reflectivity measurements.

Footprint correction (in reflectivity mode) should be best done before we do normalization

Si samples with known material, known SLD--> would that help? To have comparable geometry to work at all?
100nm etched 100 A wide roofs in Si and backfilled with Fe, to calculate expected intensity and calculate SLD that you have in the sample.

We do nano-etching with electron beam welding on the surface. Stripes should be fine, but we ned to define orientation measurement, doits would b easier.

JF: Truncated rods can be difficult , because by subtle variations of angle, the scattering pattern changes drastically.

SJ: need to find out what can be done with chemical etching and electron beam etching. Have 1cm - 2 cm in all dimensions. If you work with microsample (square mm), footprint is way largr than whatever you have.

Reference sample should have same dimensions as real sample.

JK: Even if you have the reference samples, how do they help get the correct intensity?

PG: you double-check your data reduction, you check your calibration (features at same q-values), are absolute intensities at the same value?, to know how reproducible are
It is more reproducibility.

PG: Normalization to direct beam, for GISANS we want to underilluminate (otherwise, we get lots of background)

JK: the magnetism colleagues can

JF: You measure difference in the film with contrast. If you do not know your footprint, you will not know your incident angle and the wavelength to the extend you want.

PG: All measurements we did with GISANS (large sample and small sample slits)

PG: FIGARO --> ToF-GISANS was not easy.

SJ: More and ore certain that we probably need one additional measruement:
- One reference sample
- One additional measurement with low intensity where we confine the bam very small, where footpirnt calculation becomes easier that we can use later to claibrate the measurement where maybe we can overilluminate
(JF: not sure if this will work. In your measurement where you overiolluminate, e.g. rsaolution not that good, you measure GISANS over different depths.
You do very different experiments. Might be useful but not simple scaling.)

SJ: for the moment, only simplistic approach. Without additional reflectometry, very hard to go to quantitative measurements.

AK: The approach of using the monitor will work, with sample big enough not to have overillumination problems.
PG: if it works, having GISANS with absolute intensity will be very valuable. The size of nanoparticle will define GISANS intensity.

JK: when you have strong non-specularly pattern,

PG: discussion about off-specular and cases where it influences direct beam and specular beam.
AK: you have troubles understanding where you define specular beam on the detector.

SJ: Reflectometry, we normalize to intensity of incident beam. We do specular reflectivity curve. Everything in plane is correlated, and everything not landing
on specular beam is not collected.

PG: in case that you have such strong off-specular scattering, that you influence specular intensity. Boris has published couple of papers that he proposes to deal with this problem.

JK: To get all this info, you need to simultaneously fit spec reflectivity with off-spec and GISANS and

Simultaneously: exact same beam and sample,

Footprint correction (geometric considerations for absolute intensity)

/Background handling

2026-03-18T15:21:30Z

Apostolos Vagias:

Notes:
* How do you know which type of (multiple coh/incoh.) scattering exists? And then which model for background to use accordingly? Are there approximations?
* always use multiple terms of the DWBA approximation? Where to draw the boundary?
* should we aim at always including a ray tracing approach (like McStas) to consider multiple scattering effects? (see union components McStas): https://mads-bertelsen.github.io/tutorial/Union_tutorial_1_processes_and_materials.html
* this all would strongly affect fitting of GISANS - we guess that this is one reason that no fitting of GISANS exists at the moment?
* typical approach of subtracting background doesnt work if it comes from "the sample itself, i.e., by multiple scattering in the sample"
* can this be "tested" how much the sample affects the background, are there test samples for comparison?
* why not the "typical approach": you subtract the instrument background (has to be well known), and all other "background" has to be from the sample and has to be simulated/fitted? this has then to be known for all wavelength bands and incident angles
* comparison to QENS where signals are always weak - how is that handled? Can what is known from there be taken over? QENS: Start with approximations for the model, and this then has to be refined. Also there the precise knowledge of the sample and the estimations of multiple scattering involved have to be taken into account!
* measure multiple states / dispersions / other observables to decrease ratio (unkown parameters)/(measured parameters)
* how to judge if the simulation (even if fitting perfectly to the data) is the physical correct one? For the question of which parameters are influencing the cross section mostly using bayesian fitting: see papers from Josh (for reflectometry): https://journals.iucr.org/j/issues/2021/04/00/ge5096/ge5096sup1.pdf

*****
group 1

JF:
Alexandros: going to a corner and measuring bkg

Philipp: this corner you go is below/or above the horizon/
Alexandros: below.

Philipp: below the horizon, you have negative intensities. the corner will be different below or above the horizon.

Alexandros: yes, because you have something that absorbs and scatters at the same time.

Philipp: better to take it below the horizon instrument background.

Alexandros: problem we had usually with bare substrate, we had no other way to estimate bkg.

JF: the incoherent signal you get is not as constant in angle as you expect.

SJ: in GISANS, closer to footprint, after 2 cm is all incoherent.
JF: and inelastic
SJ: instruments masuring reflectometry and GISANS, first you scan through angle (and identify critical edge).
then, use this approach to get average SLD of the sample. problem with this approach would be that no SANS instrument can use this approach. put sample in, first reflectometry (get SLD) and afterwards then GISANS.

intensity and wavelength

Henrich: a SANS machine can do everything a reflectometry machine can do.
Philipp: can cover some angular range to see total reflection, but with poor resolution.

JF: for subtle variations of SLD maybe not possible. we try to measure reflectivity curves when we do GISANS measurements.

SJ: is always worth it.

/Multiple Scattering

2026-03-18T14:28:47Z

Apostolos Vagias:

Group 1

Philipp:Distorted Wave Born Approximation, is some sort of multiple scattering, because incoming beam is split into reflected and refracted beams?

Joachim: reflection from interface can be described as scattering, in Sinha paper, they discuss scattering from infinite volume and then describe reflection. Known way to deal with reflection and refraction, this gives DWBA. Scattering is not by interfaces, they are taken into account by DWBA.

Henrich: Parratt algorithm is a dynamic approach. it takes into account multiple reflections. Do not know how it can get more precise.

'''reflection and refraction should be excluded from multiple scattering'''

If we calculate all transmission and reflection coefficients, we are left with 16 reflection and transmission combination terms. Some have different momentum transfers. this is shown like reflection/refraction, reflection/reflection. should we call this multiple scattering?

Ammat: Multiple scattering: Born approximation is single scattering event. Multiple scattering comes with further scatterign events, is not included in DWBA. magnetic interactions. when they are important, we cannot reply on Born approximation, but use multiple scattering in solid state. when first scattering event happens, system responds. this process continues. is a dynamical process, not single kinematical process.

'''Need to decouple between "Dynamic" term bing different than dynamic (meaning energy transfer)'''

Boris: full solution, we have to consider changes in the sample. even i first order scattering calculations,

Philipp (question to Boris): have you ever confused the term dynamic scattering with inelastic scattering?
Boris: with ToF is feasible. 100 neV (depends on wavelengths), to see this you need reasonable resolution in pulse. perfect for SNS, here at ILL we have rather broad pulse.

experiment from Sascha Frank on standing/moving waves. if it is standing waves, density gives periodic structure and same stripes. alternatively, if we have one magnon / phonon, we have one branch (stokes/antistokes). the excitations produce the harmonic.

Philipp: we consider higher orders of BA as multiple scattering?
Boris: Born series valid for amplitudes and valid within the transverse coherence lengths, that all interfaces produce one plane wave in same direction if we have lateral homogeneity and interfere with each other. but, multiple scattering when events occur in sequence but are incoherent in between of them. it could be multiple specular reflection, but gap should be greater than transverse coherence length (where particles reflect multiply within 1 cm gap). It may look like a semantic difference. You take interference between events or not? multiple scattering requires than path length is much greater than mean free path (1/Sigma_total*density of the particles).

'''Joachim: multiple scattering (in book of Sears) is treated in terms of transport theory.'''
need to have a distance to avoid interference

Philipp: higher order BA should not be called multiple scattering. would it make sense to call it coherence?
Boris: case of neutron guide (each reflection is quantum mechanic, superrmiror, each collision is not correlated with eachother), case of waveguide (there is resonance layer in between, it is expected with microbeam waveguide where they try to get from edge of the sample and nothing comes in, because it violates the coherence). isndie, they are all coherent from top to substrate, in substrate it goes trhough the edge.
if sample is smaller than coherence length,

Philipp:H'''enrich, do you calculate with matrix formalism reflection and transmission in each layer and you use them to calculate incoherent multiple scattering in each particle? so, this mode that calculates z-amplitude is calculated?'''
Henrich: '''this is what I want to do.'''
Boris: if you shoot through the dge and look through the other edge, is feasible. if thre is resonance layer in between, 10 microns layer and look through the edge maybe

Boris: forming microbeams using resonance layers as waveguide is OK, only when you come from the edge. only there, you will get enhancement from the other edge. Mean free path for neutrons is cm or few mm. for 1cm , I hav one particle only.

Henrich: '''can I have several scattering events independently?'''
Boris: '''if the distance is much greater than mean free path (1/N*Sigma_total, roughly few mm)'''

Philipp: multiple
Boris: particle, part goes in forward direction and (multiple scattering does not play a role in reflectivity)

incoherent sum of reflectivities.

Henrich: if you come with alpha_i> alpha_c, in the deptth, you can have independent events. if alpha_i< alpha_c, multiple scattering does not play a role.

Boris: In lateral direction, wave that propagates. if we have 1m, we have

Joachim: what is typical thickness of samples in conventional SANS?
Henrich: 1mm to 5mm (5mm stronger intensity. mean free path length that decides. total scattering cross-section that determines

Boris: '''for cold neutrons, mean free path ~few mm. but, cohereence length projection 100microns, the sample should be larger than that. we have 2 constraints (one from coherence length and one from mean free path length, both compared to sample dimension).'''

if sample is too long, will not prevent multiple scattering happening. as long as the coherence effects are averaged out, we can have

Boris: coherence length 0.1mm, sample size 1 cm laterally. That what we usually use to fit reflectivity, we have many thousands of these coherence spots, we averaged modulus square of reflectivity. incoherent sum of all coherence length (this is why it is proportional to projected areas on the beam). with very slow neutrons, this is possible, but nothing penetrates. example is whispering gallery. when there is multiple reflection from different mirrors circled around, one can turn direction of neutron (1cm radius and coherence length is 1mm) --> in such situation, multiple off-specular scattering. but this is curved surface

/Multiple Scattering

2026-03-18T14:07:28Z

Apostolos Vagias:

Group 1

Concerning slide where we define "nomenclature"

Distorted Wave Born Approximation, is some sort of multiple scattering, because incoming bam is split into reflected and refracted beams

Joachim: reflection from interface can be described as scattering, in Sinha paper,m thye discuss scattering from inginite volume and then describe reflection. Known way tod eal with reflection and refraction, this gives DWBA. scattering is not by interfaces, they are taken into account by DWBA.

Henrich: Parratt algorithm is a dynamic approach. it takes into account multiple reflections. Do not know how it can get more precise.

reflection and refraction should be excluded from multiple scattering

if we calculate all transmission and reflection coefficients, we are left with 16 rflection and transmission combination terms. some have different momentum transfers. this is shown like reflection/refraction, reflection/reflection. should we call this multiple scattering.

Ammat: Multiple scattering: Born approximation is single scattering event. Multile scattering comes with further scatterign events, is not included in DWBA. magnetic interactions. when they are important, we cannot reply on Born approximation, but use multiple scattering in solid state. when first scattering event happens, system responds. this process continues. is a dynamical process, not single kinematical process.

"Dynamic" term different than dynamic (meaning energy transfer)

Boris: full solution, we have to consider changes in the sample. even i first order scattring calculations,

Philipp (question to Boris): have you ever confused the term dynamic scattering with inelastic scattering?
Boris: with ToF is feasible. 100 neV (depends on wavelengths), to see this you need reasonable resolution in pulse. perfect for SNS, here at ILL we have rather broad pulse.

experiment from Sascha Frank on standing/moving waves. if it is standing waves, density gives periodic structure and same stripes. alternatively, if we have one magnon / phonon, we have one branch (stokes/antistokes). the excitations produce the harmonic.

Philipp: we consider higher orders of BA as multiple scattering?
Boris: object, because Born series valid for amplitudes and valid within the transverse coherence lengths, that all interfaces produce one plane wave in same direction if we have lateral homogeneity and interfere with each other. but, multiple scattering when events in sequence but incoherent in between of them. it could be multiple specular reflection, but gap should be greater than transverse coherence length (where particles reflct multiply within 1 cm gap). may look like a semantic differenc.e you take interference between ecvents or not? multiple scattering requires than path length is much greater than mean free path (1/Sigma_total*density of the particles).

when BA is valid, or,

Joachim: multiple scattering (in book of Sears) is treated in terms of transport theory.
need to have a distance to avoid interference

Philipp: higher order BA should not be called multiple scattering. would it make sense to call it coherence?
Boris: neutron guide (each reflection is quantum mechanic, superrmiror, each collision is not correlated with eachother), waveguide (there is resonance layer in between, it is expected with microbam waveguide whre thy ry to get from edge of the sample and nothing comes in, because it violates the coherence). isndie, they are all coherent from top to substrate, in substrate it goes trhough the edge.
if sample is smaller than coherence length,

Philipp:Hnrich, do you calculate with matrix formalism reflection and transmission in each layer and you use them to calculate incoherent multiple scattering in each particle? so, this mode that calculates z-amplitude is calculated?
Henrich: this is what I want to do.
Boris: if you shoot through the dge and look through the other edge, is feasible. if thre is resonance layer in between, 10 microns layer and look through the edge maybe

Boris: forming microbeams using resonance layers as waveguide is OK, only when you come from the edge. only there, you will get enhancement from the other edge. Mean free path for neutrons is cm or few mm. for 1cm , I hav one particl only.

Henrich: can I have several scattering events independently?
Boris: if the distance is much greater than mean free path (1/N*Sigma_total, roughly few mm)

Philipp: multiple
Boris: particle, part goes in forward direction and (multiple scattering does not play a role in reflectivity)

incoherent sum of reflectivities.

Henrich: if you come with akpha_i> alpha_c, in the deptth, you can have independent events. if alpha_i< alpha_c, multiple scattering does not play a role.

Boris: In lateral direction, wave that propagates. if we have 1m, we have

Joachim: what is typical thickness of samples in conventional SANS?
Henrich: 1mm to 5mm (5mm stronger intensity. mean free path length that decides. total scattering cross-section that determines

Boris: for cold neutrins, mean free path ~few mm. but, cohereence length projection 100microns, the sample should be larger than that. we have 2 constraints.

if sample is too long, will not prevent multiple scattering happening. as long as the coherence effects are averaged out, we can have

Boris: coherence length 0.1mm, sample size 1 cm laterally. That what we usually use to fit reflectivity, we have many thousands of these coherence spots, we averaged modulus square of reflectivity. incoherent sum of all coherence length (this is why it is proportional to projected areas on the beam). with very slow neutrons, this is possible, but nothing penetrates. example is whispering gallery. when there is multiple reflection from different mirrors circled around, one can turn direction of neutron (1cm radius and coherence length is 1mm) --> in such situation, multiple off-specular scattering. but this is curved surface

/Multiple Scattering

2026-03-18T13:46:45Z

Apostolos Vagias: