Author Topic: Penepma/Penfluor/Fanal Sulfur Ka in Carbon  (Read 11290 times)

Les Moore

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Re: Penepma/Penfluor/Fanal Sulfur Ka in Carbon
« Reply #15 on: December 04, 2014, 03:45:06 PM »
Thanks,

Now I know what I am doing over the Christmas break!

Les

NicholasRitchie

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Re: Penepma/Penfluor/Fanal Sulfur Ka in Carbon
« Reply #16 on: December 05, 2014, 12:17:29 PM »
First, the absorption correction acts as expected.  It is smaller at 5 keV than 15 keV.  Second, the increase in the total correction seems to result from an increase in the Z correction (both stopping power and backscatter correction.)

It is not obvious from staring at the Bethe energy loss equation why the difference would be so large for the difference in stopping power (see attached PDF).  It is equivalently unintuitive why such a small amount of C has such a large influence on the backscatter correction (the mean atomic number does not change by much.) However, these calculations are much more challenging to understand than the absorption correction which simply depends upon MAC and path length.

Simulating this measurement in DTSA-II shows that the analytical matrix corrections are consistent with Monte Carlo calculations so if there is an error then it manifests itself in both analytical and Monte Carlo calculations.

Edit by John: Thanks Nicholas! A nice physics intuition mystery.

For those just reading this, here is the post containing the graph Nicholas and I are trying to explain:

http://probesoftware.com/smf/index.php?topic=398.msg2019#msg2019
« Last Edit: February 09, 2015, 07:43:39 PM by John Donovan »
"Do what you can, with what you have, where you are"
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Les Moore

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Re: Penepma/Penfluor/Fanal Sulfur Ka in Carbon
« Reply #17 on: December 05, 2014, 04:09:45 PM »
hi John,

An intuitive thought: if the S is dilute, which it is, the electrons on average may interact with C before they get to the S atoms. This means that the average energy they have by the time they get to the sulphur atoms is lower than the beam energy and thus closer and closer to the minimum excitation energy.  Given that, there should be no such effect at high S concentrations.

I would imagine that K in S would kick up at about 7kV and Fe in C at about 12 kV.

Les 
 

Probeman

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Re: Penepma/Penfluor/Fanal Sulfur Ka in Carbon
« Reply #18 on: December 08, 2014, 05:18:35 PM »
There may be some confusion here.

Les was originally discussing an emitter (S ka) at the 1% level in a 99% matrix of carbon.  So I modeled that as seen in the graph here:

http://probesoftware.com/smf/index.php?topic=47.msg2019#msg2019

along with some other emitter-absorber combinations. That's when I called in the "big gun" Nicholas Ritchie at NIST to help explain things.

When Nicholas chimed in with a post labeled "1% C in S at 5 keV and 15 keV" I thought, well maybe he misread our discussion, but I thought I might as well model the emitter at the 99% level even though the matrix effects will obviously be close to 1.

So here is that graph (99% emitters in a 1% absorber matrix):



and the Ti ka matrix correction at 10 keV? Well they really are all slightly different- so I didn't use the same value accidentally.

But what the heck occurs at 10 keV for Ti ka in these absorbers?
The only stupid question is the one not asked!

Les Moore

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Re: Penepma/Penfluor/Fanal Sulfur Ka in Carbon
« Reply #19 on: December 08, 2014, 07:59:38 PM »
Hi John,

Now I'm looking at condensation materials in the blast furnace and one of them is a graphite phase, unlike any seen so far in the blast furnace so far.  It is mostly C with ~5%K.  This might be a KxC60 buckyball condensate. 

More modelling.

If the blast furnace does turn out to be a buckyball generator and we could get it out, it would be worth substantially more than the iron we produce  ;D

Les