[GSAS-II] use K-beta lines?

[William Boyer]

Thank you for your suggestions.
In computing the pattern all over again for the K beta lines (yeah, the LP and asymmetry due to axial divergence and IDK what else would be significantly different), could GSAS be told to calculate a second pattern using the k beta wavelength and add it to the K alpha pattern?

Proto diffractometers that use XRF-type detectors can save the full spectrum from each data point.  Then after one scan, generate additional diffractograms using different energy windows from the saved spectra. 😊So that does sound like good idea, but …

I have data already collected with low energy resolution (linear detector).  If I split my patterns up into pieces with K alpha data and regions with K beta data, can GSAS work with XYE data that is discontinuous?

Thank you very much,
William Boyer

From: Toby, Brian H. <toby at anl.gov>
Sent: Wednesday, September 25, 2024 3:51 PM
To: William Boyer <wboyer at protoxrd.com>; gsas-ii at aps.anl.gov
Subject: Re: use K-beta lines?

This is something that I have thought about myself, too. The quick answer is this is not something that can be done simply. The Kalpha2 & alpha2 wavelengths are so close that all that is done is to shift each peak computed for alpha1 to the location of alpha2, multiply it and add it. Very quick and easy. We don’t have a mechanism to handle more that two wavelengths, but open source means that in theory the code could be changed to handle more than alpha 1,2 (though I am not convinced that the other components matter for all but the most finicky of computations). K beta is a different issue. That wavelength is different enough that one needs to compute the pattern all over again and perhaps even have a second set of instrumental profile terms. Also possible to do, but certainly not implemented.

Depending on the problem, the gains from using all the incident photons without a filter or analyzer could be really valuable and would overcome the disadvantages of having three rather than two wavelengths, so I can see reasons why one might want to do this. However, there are energy dispersive detectors x-ray detectors that can easily separate K alpha from K beta (not alpha 1 from alpha 2 though). An energy-dispersive detector coupled with two MCA’s would allow you to collect separate K alpha and K beta patterns from a single scan. With that one could do a two-histogram fit in GSAS-II. That would offer the best of all worlds IMO.

Brian

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