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Investigating multiple scattering with McStas

Investigating multiple scattering with McStas. James Tricker Mantid Vacation Student. Multiple scattering. Can minimise MS in experiments by using a sample that is: Small in comparison with its mean free path. Strongly absorbing

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Investigating multiple scattering with McStas

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  1. Investigating multiple scattering with McStas James Tricker Mantid Vacation Student

  2. Multiple scattering Can minimise MS in experiments by using a sample that is: • Small in comparison with its mean free path. • Strongly absorbing When we do have MS we would like perform corrections on our data so it appears to contain only single scattering event and the neutrons have undergone no absorption

  3. Integrating over a sample: dV1 l1 l12 l2 dV2 The neutron intensity undergoes exponential decay as it passes through a sample Trying to do this rapidly becomes intensive Successive terms converge to zero Can simplify the calculation in some cases

  4. What can Mantid do currently? Mayers Sample Correction Multiple Scattering Cylinder Absorption (MSCA) Muscat First two assume the sample is a cylinder and that scattering is elastic and isotropic - essentially restricted just to vanadium Muscat is quite dated and not widely used but in principle a good general method

  5. Cylinder absorption

  6. Full comparison

  7. A general tool for simulating neutron scattering instruments and experiments Great for multiple scattering investigation. Can track how many times individual neutrons have scattered before detection. Possible to simulate scattering inside complicated geometries and between the sample and surrounding environment

  8. Suggested approach utilising McStas Generate a scattering function S = S(Q) or S(Q, omega) from the data in question using Mantid Making the assumption that multiple scattering for S does not contain multiple scattering and is good first order approximation of the true S of the sample Insert this S into a McStas component and do a McStas simulation where the output of this simulation is separated into single and multiple scattered neutrons

  9. Mantid and McStas From the McStas instrument file generate the IDF file for Mantid. Compile the McStas c code. (Remember to link correctly to NeXus libraries) Run McStas simulation with the NeXus flag on to produce event data for Mantid. This can already by somewhat automated Research being done to bring OFF to Mantid Always improving interoperability

  10. Investigation with McStas Disclaimer: Some potential flaws in this analysis. See full report for a discussion of this or ask at the end

  11. Investigation with McStas

  12. Further Information • McStas • http://www.mcstas.org • McStas Union components for simulating multiple scattering • http://media.mcstas.org/ESS_DMSC_20161117/DMSC_talk_MBertelsen_McStas_Union.mp4 • Slides and full report • https://github.com/mantidproject/documents/tree/master/Presentations/Multiple%20Scattering%20Presentation

  13. Questions?

  14. Why might the investigation be flawed?

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