Discussion Group B2
Collaborative development of reference and calibration standards and the next round robins
- Adrian Rennie
There were no specific formal presentations made during this discussion session. An introduction to the topic had been provided by the earlier talk of Adrian Rennie: Learning about SAS from Round-Robin Measurements .
What is needed?
We started by asking what people would like from 'round-robin', 'reference' and 'calibration' samples.
As regards calibration there is need to verify:
- momentum transfer
The sample should be stable, non-toxic and should be available in sufficient quantity to be spread widely. It is desirable that samples are easy to measure: eliminate user errors. Scattering should be sufficiently strong that measurement times are reasonably short.
It was noted that no single sample might be ideal for all of these purposes across a range of instruments for both X-ray and neutron scattering. Some of the difficulties with presently available samples were discussed.
Ideas for new samples for comparative measurements
Several ideas for samples were discussed and it was recognized that some of these would need initial tests as they had not been tested. These were also presented and augmented in the general discussion.
Some ideas that were mentioned are:
- copolymers that show a correlation peak (e.g. styrene/polyisobutylene from Kraton)
- microfabricated samples such as gratings
- deuterated sodium dodecyl sulfate crystals
- polymers filled with silica or other particles
- Irradiated light metals with pores
- metal alloys with precipitates - iron or nickel (e.g. WASP alloys) based
- patterned gold foils: Nano fabricated materials,e-beam fabricated samples
- anodized aluminium foils
- photo patterned polymers
- lithographically-prepared samples
- crystallites in glasses (quantum dots)
It was noted that some of these ideas for samples do not represent readily available samples and that it would be necessary to make tests or engage in preparatory work. Participants were encouraged to try these and then engage further with others for initial comparative tests or at least measure with their own instruments.
A further list of samples that are now available and could be circulated to further laboratories was drawn up
- Silver behenate from a single batch
- Porous carbon
- Polystyrene latex particles (from previous round robin)
Remarks about Silver Behenate
Discussion about silver behenate samples noted that apart from the well-known possibility of thermal and light induced degradation, some samples apparently showed different 'c' lattice parameters as determined from the 00l Bragg reflections. Care could be needed to dry the sample carefully. A further comment was that X-ray data that is measured at high resolution can show asymmetric peak shapes that could complicate the simple determination of the position. Measurements with neutron (SANS) instruments do not usually resolve the peak shape.
Samples of the same latex (PS3) as measured in previous comparative measurements are still available and diluted samples could be provided to laboratories interested in making further measurements.
Some information about the previous results is shown on this wiki and in a publication. See Latex Round Robin .
For SAXS measurements it is possible to use samples dispersed in a mixture of ethanol and water. This increases the contrast so that the signal is less dominated by the surface functionality.