[GSAS-II] Absorption correction of TOF neutron powder diffraction

[Diogo Fernandes De Almeida]

Dear all,

Apologies in advance if this is something I could easily find in the documentation, but I've spent some time looking and couldn't find anything. If there is a suitable reference I could be pointed to I would be very appreciated!

I'm having some trouble finding how absorption correction works in time-of-flight neutron diffraction data. I have a dataset which has already been absorption corrected in the data-reduction process from an experiment at a neutron source. However, I notice a significant improvement in goodness-of-fit by visual inspection of the pattern by refining absorption in Sample Parameters, particularly of the higher d-spacing / lower Q peaks. Extinction is also refined but alone can't account for the difference I see, and neither do isotropic atomic displacement parameters.

My problem is that the GSAS-II GUI says the absorption value being refined is mu*r/lambda, which as far as I understand only works for monochromated radiation. I found some documentation in the GSAS technical manual related to this:
It is assumed for TOF data that the linear absorption of all components in the sample varies with 1/velocity, and it is indistinguishable from multiple scattering effects within the sample.
Does this mean I should not refine absorption at all for TOF data, and all effects should be account for during the data-reduction process? Or does it mean by refining this parameter I'm actually accounting for multiple scattering instead of absorption?

Thank you for reading this far and for any help you can provide!
Best wishes,
Diogo
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