Discussion Group B1

Discussion Leaders

• Charles Dewhurst (ILL)
• Brian Pauw (NIMS)

Presentations

• Presentation by leader: Nomadic utopia:

towards a better understanding of all instrumental artifacts - Charles Dewhurst

Discussion Notes

Discussion on Data Corrections (N=neutrons, X=X-rays)

Detectors:

There are a lot of stories on what not to do. I would be nice to put some of these stories online. Some advice:

N Don’t stagger detector tubes, the partial shielding is nontrivial to correct for (Ken Littrell)
N recalibrate position every so often to compensate for stretch and offset caused by charge division electronics instability.
N Coincidence detectors are difficult to correct for (with the compensation dome on top)
N Boron technology detectors will have their own issues, corrections and complications.

X Not able to measure direct beam on the same detector. Can be resolved by:
 -  partially transparent beamstop,
 - attennuator as beamstop
 - pin-diodes (should be placed close to sample to determine transmission according to Richard Heenan’s definiton).
X Difficult to measure flat field, can be done by:
 - Glassy carbon,
 - moving detector across the beam
 - Careful when measuring: only flat field should be determined, not the other corrections!

Other advice:

- Add resolution in SAXS and SANS, both lab and facility
- Minimise air in all techniques!
- how to deal with resolution?
- traceability of corrections are needed (provenance)
- calibration sample should be available at facilities
- much more information needs to be available everywhere (make a list?)
- Desmear on lab-sources
- How far can you correct with background correction?
N TOF choppers can be a big source of background.
N Shield around active elements (and put holes in the right place)
N Cover aigrets with absorbing tubes
N Recommended slit design: use B4C with sintered edge.