Absorption correction for cylindrical samples

[celinedurniak]

Executive summary

Calculate and apply absorption correction for cylindrical samples in Powder Diffraction

Context and background knowledge

For example, see algorithms in Mantid

AbsorptionCorrection

CylinderAbsorption

SNSPowderReduction in Mantid to check when the absorption correction is applied within the whole workflow

Inputs

Scipp data structure from loaded NeXus or csv file(s)

Assumption: the input should be expressed in wavelength

Note that information about the sample (chemical formula, geometry, mass density, number density...) might be stored in the sample log of the file or must have to be provided by the user when using the algorithm.

Methodology

See source code from (Mantid) references above

Assumption: we consider only cylindrical samples for this first implementation

Acceptance criterion Absorption correction step is implemented in ESS Diffraction worflow (https://scipp.github.io/ess/instruments/external/powgen/powgen.html)

Outputs

This requirement should provide the absorption correction term and the corrected sample data

Which interfaces are required?

Integrated into reduction workflow, Python module / function

Test cases

• As input file, use POWGEN event file provided in Mantid (PG3_4866_event.nxs or PG3_4844_event.nxs) and already used in ESS Diffraction workflow. In this case, the output from the implementation in Scipp could be compared with what we get from Mantid.
• CSV files from DREAM (also available in Scipp documentation)

Comments

Followup Work: Extend this implementation to:

• other sample shapes
• several components (sample, container)
• using other assumptions (like ‘FullPaalmanPings’)

[SimonHeybrock]

Before implementing, we should consider if the actual correction should be part of ScippNeutron, since it is very generic. ESSdiffraction would then only contain the workflow integration, imported from ScippNeutron.

[jl-wynen]

Removed from essentials milestone because it is unclear whether this should be done during reduction or analysis. Postponing implementation until we have clarity.

[jokasimr]

Still needs to apply correction in diffraction workflow