Author Topic: MAN fit - ?Fluorescent? standards?  (Read 795 times)

JakubHaifler

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Re: MAN fit - ?Fluorescent? standards?
« Reply #15 on: July 15, 2019, 03:22:46 pm »
Hi Ben and John,

to be honest, I did not have any special physical theory on that phenomenon. I just wanted to point out that I observed the same behaviour on synthetic cheralite. And actually, the observation of a very strong photoluminescence also agreed. But later, I was thinking about it a little bit. A strong photoluminiscence usually occurs when e.g. quartz is exposed to electron beam. Given that MAN method is applied on quartz, I guess someone would have observed such phenomenon. 

Many thanks for the explanation. I will need to find something about the alternative expression of the Z-bar.

Best regards, Jakub Haifler.
Department of Geological Sciences
Masaryk University
Brno, Czech Republic

Probeman

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Re: MAN fit - ?Fluorescent? standards?
« Reply #16 on: July 16, 2019, 12:48:37 pm »
Hi Jakub,
No worries.

Actually I blame myself.  I published on these electron (or Z) fraction based Z-bar calculations for both elastic scattering and continuum production 20 years ago. At the time I thought the effects would not be so significant for normal EPMA work.

But then people more recently starting utilizing high Z materials in their MAN background fits, which allows for a greater possibility of compounds with very different A/Z ratios. And again, Ben Buse starting the elastic scattering discussion again with his re-discovery of the Z-bar effect when running BSE simulations in Penepma and WinCasino.

Now I realize that these effects are significant enough, especially in the case of high Z elements. So indeed we should be implementing these new Z-bar calculations into our quantitative software. This has been done in Probe for EPMA for the MAN curves, as shown in several posts above.

On the Z fraction elastic scattering Z-bar calculations, I am working with one of our colleagues on modifying perhaps the Pouchou & Pichior backscatter loss equations, and hopefully we'll have something to show later this year.  It turns out that everyone in the past just assumed that BSE loss simply scales with mass!  How silly of us...  :D

But in the meantime you can read the abstract on elastic scattering that I will be presenting at M&M next month in Portland which is attached to this post:

https://probesoftware.com/smf/index.php?topic=1111.msg8249#msg8249

The thing that amazes me is that both continuum production *and* BSE loss are well modeled by applying the Z^0.7 Z fraction average atomic number equations. Two completely different physical processes...
« Last Edit: July 16, 2019, 03:55:09 pm by Probeman »
The only stupid question is the one not asked!

Probeman

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Re: MAN fit - ?Fluorescent? standards?
« Reply #17 on: August 05, 2019, 08:02:10 am »
Yesterday at the M&M social Peter Statham reminded me of a paper he sent me in 2016, where he independently derived a fit for continuum production with Z, and where he found a Z exponent of 0.75.  Which is quite close to 0.70.

I attach his 2016 paper and my original 2002 papers (BSE and Continuum) below (please login to see attachments). In another cute coincidence of science, please see fig. 3 in both papers!

I also include this screen shot of an Excel spreadsheet with a summary of the Z exponents for Ben Wade's MAN fits to continuum data:



If you're at M&M and see me, please feel free to ask me what the color coding represents, though you may indeed figure it out before I explain.
« Last Edit: August 09, 2019, 09:11:36 am by Probeman »
The only stupid question is the one not asked!