Author Topic: F Ka ROI artifact  (Read 5075 times)

Probeman

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    • John Donovan
Re: F Ka ROI artifact
« Reply #30 on: November 20, 2017, 02:30:33 PM »
I have a question about the shape of the MAN background calibration curve.  Sometimes when one plots up a large range of average Z, the trends show a positive curvature where the continuum intensities decrease with increasing Z as seen here:

http://probesoftware.com/smf/index.php?topic=4.msg5136#msg5136

For light elements or other low energy emission lines this could be due to increasing absorption in higher Z matrices, but the MAN absorption correction should deal with that I would think.  So what else could it be?  Obviously there is more backscatter at high Z, so there are fewer electrons staying in the matrix and hence less continuum x-ray generation. Also higher Z elements tend to produce less intensity for a given emission line since there are so many other probabilities for absorption and fluorescence (and emission).

From that same zircon run above here is the MAN curve for Hf Ma (a relatively low energy emission line) with the continuum absorption correction applied:



and here is the same data without the continuum absorption correction applied:



But the difference in curvature is slight. We need a suite of low energy x-ray emission lines measured over a large range of average Z to see better what is going on with continuum emission.
« Last Edit: April 12, 2020, 07:51:06 PM by John Donovan »
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Probeman

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Re: F Ka ROI artifact
« Reply #31 on: November 28, 2017, 04:20:17 PM »
Last month Ben Wade posted this interesting observation of a mystery emission line near F Ka in TiO2:

http://probesoftware.com/smf/index.php?topic=4.msg6305#msg6305

Here is a plot of fluor-phlogopite and TiO2 normalized intensity.  I wanted to see if I could say whether the mystery line was a first order emission line or not:



Just eyeballing it I'd say it looks about as wide as the F Ka emission, so yes, I think it is a first order line, but next I'll try some really high precision wavescans.
john

Remember we noticed that we were seeing a very weak peak (possibly Ti) interfering with F Ka, but only for TAP crystals?  The above plot scan is from my SX50 which just has normal sized TAP crystals (but using 60 sec per point), so I thought I would try again on my SX100 using the LTAP crystal and double the counting time expecting to see some even nicer looking peaks (we used 15 keV and 50 nA for all scans). 

My first attempt surprised my students and I because there was no peak there!  Here is using a LTAP crystals and 120 sec per point for TiO2 and Ti metal:



So then I said, OK let's try 300 sec per point, and we got this:



Pretty disappointing.  This tells me that this peak is spectrometer/crystal dependent but still related to Ti content. I would guess that some cracks in the Bragg crystal are causing a secondary diffraction from some Ti emission and that is what we are seeing.

Here is a summary of Ti, TiO2, SrTiO3 and FeS2 with fluor-phlogopite as a F ka peak reference:



I expect that my old Sx50 has a more cracked TAP and that is why this mystery peak artifact is more visible even at much shorter counting times.

I don't know what else to say...
john
« Last Edit: April 12, 2020, 07:51:31 PM by John Donovan »
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BenjaminWade

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Re: F Ka ROI artifact
« Reply #32 on: November 28, 2017, 05:36:48 PM »
Hi John
That is interesting. I guess that means both my TAP and LTAP are cracked or have defects then, much more so than your LTAP, as I see the mystery peak quite large at relatively on both. I have another TAP on sp2 I haven't checked but chances are its on that as well. Going by Owen's poor LTAP it looks like it could be quite prevalent. Would TAP xtals be more susceptible to internal stresses/damage over time than other crystals with different d-spacing? I couldn't imagine why really. Perhaps its on all xtals to some extent.

cheers

Probeman

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Re: F Ka ROI artifact
« Reply #33 on: November 29, 2017, 05:53:56 PM »
Hi John
That is interesting. I guess that means both my TAP and LTAP are cracked or have defects then, much more so than your LTAP, as I see the mystery peak quite large at relatively on both. I have another TAP on sp2 I haven't checked but chances are its on that as well. Going by Owen's poor LTAP it looks like it could be quite prevalent. Would TAP xtals be more susceptible to internal stresses/damage over time than other crystals with different d-spacing? I couldn't imagine why really. Perhaps its on all xtals to some extent.

cheers

Hi Ben,
I really have no idea.  If this peak is indeed merely a diffraction artifact, then the defects in the Bragg crystal might not even be visible to the eye.
john
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sem-geologist

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Re: F Ka ROI artifact
« Reply #34 on: May 31, 2021, 04:41:54 AM »
Sorry for bringing up an old post, but I can confirm that this artifact is also visible on all our TAP crystals on SX100 and SXFiveFE. So it is rather not the mere artifact, but some systematic artifact. It reminds me a bit terrible systematic artifacts on all of our LPET's, which I guess are X-ray reflection from backside of diffracting crystal.