SAXSLAB’s GANESHA (Calibration without Standards)
When we claim that no standards are needed for SAXSLAB’s GANESHA, it is because the tools available for so-called primary calibration are ALL available within the SAXS/WAXS system.
For q-calibration we usually use silver behenate, but because the GANESHA can move the detector with an accuracy of a fraction of a millimeter, we can measure the scattering pattern at many different sample-to-detector distances. When the q-calibration is correct, the peaks will accurately overlap for ALL the measurements. If they do not, we conclude that the calibration is off by a fixed distance, which we can then find using the measured peak locations. And finally If they overlap perfectly, but do not give the correct value for the silver behenate peak, we know it is time to change the silver behenate. So really the GANESHA does not need a q-calibrant, it just needs something with a well-defined peak.
And as for absolute intensity, it really boils down to knowledge of 3 things:
- Do we know how many photons hit the sample?
- Do we know how many photons were stopped in the sample?
- Do we know how many scattered photons went where?
In SAXSLAB’s instrumentation, those values are indeed all known to a few percents accuracy. The rest is just applying the math.
And thus we boldly claim any of our instruments with moving detector to be instruments with “no standards needed”, because no other standards will get you that close to the truth.
If you want to read a bit more about the way we do these things take a look at our Technical note on the right. And of course you are always welcome to contact us for a more detailed discussion of how justify those claims.