Author Topic: Assessing Accuracy in CalcZAF  (Read 3211 times)

Thomas

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Re: Assessing Accuracy in CalcZAF
« Reply #15 on: May 23, 2020, 02:47:33 am »
Hi Brian and John,
thanks for the helpful comments!
Unfortunately, I was not able to find any detailed description of these correction procedures in the JEOL manual. But I will discuss this topic with the JEOL staff!
Regards, Thomas

Thomas

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Re: Assessing Accuracy in CalcZAF
« Reply #16 on: May 27, 2020, 11:39:15 am »
Hi Brian and John,
I would like to announce some "open questions" after performing the calculations mentioned by Brian on May 22.
First, if the Z value of c. 28 for N in the BN standard would be equal to the area below the PRz curve (i.e. the "primary intensity") carrying units of g/cm2, then it cannot - in my opinion - represent a correction factor for the atomic number effect in the ZAF matrix correction. However,  the "ZAF Fac" in the published file is calculated by ZxAxF as you can see.
I have further tried to calculate (R/S)x(1/Q(E10)) for N but was not successful to reproduce the value of about 28.
When I recalculated my BN data by using the CITZAF (i.e., PRz) method, I got values for the Z factor (given as (1/s-el)x(r-el)) of about 1 and not 28, i.e. quite different to the ZAF correction method..
May I ask you to explain this disreppancy?
Regards, Thomas


Brian Joy

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Re: Assessing Accuracy in CalcZAF
« Reply #17 on: May 27, 2020, 07:02:37 pm »
Hi Thomas,

I don't know exactly what the Z values printed out by the JEOL software represent.  (I'm referring to the 28.0 for N Ka and 78.5 for B Ka in BN.)  They are much too large to represent the actual atomic number corrections, and so I deduced that they are Z values for the X-ray of interest in the unknown before division by the respective value obtained from the standard using the same model.  Without units attached to these quantities, they are difficult to interpret.  Since only the ratios relative to the standard are used to calculate concentrations in the unknown, the units typically are not specified.  This is bad practice, and it can create nightmares for those of us who want to figure out how the calculations are done.  The A values presented are relatively easily identifiable as f(chi), which is dimensionless.

Also, I should point out that the area under phi(rho*z) wouldn't necessarily have to be stated in units of mg/cm^2, but it must carry units of mass per area (so it could be μg/km^2 or g/cm^2, for instance).  I was a little sloppy in my original statement.  Note that phi(rho*z) itself is dimensionless.

If you are interested in exploring how the Z and A factors are calculated realistically and precisely (and with identifiable units), then I suggest that you read through the presentation by Pouchou and Pichoir in "Electron Probe Quantitation" (aka "the green book") -- I've attached their paper; the basics are covered in pages 31-45.  Note:  it is not easy reading!  Also, note that typos are present in equations 13 and 21.  If you want, I can send you some Fortran code that I wrote based on this presentation.
« Last Edit: May 27, 2020, 07:44:01 pm by Brian Joy »
Brian Joy
Queen's University
Kingston, Ontario
JEOL JXA-8230

John Donovan

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Re: Assessing Accuracy in CalcZAF
« Reply #18 on: May 28, 2020, 08:55:02 am »
Thomas,
Also note that the entire CalcZAF source code is available to all on Github as described here:

https://probesoftware.com/smf/index.php?topic=570.msg3245#msg3245

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Thomas

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Re: Assessing Accuracy in CalcZAF
« Reply #19 on: May 28, 2020, 09:46:16 am »
Hi Brian and John,
thanks for the comments and the links!
During the last weeks, I have tried to find out how to calculate in detail the Z and A correction based on Duncumb & Reed and Philibert by creating a simple excel sheet. I was able to reproduce the CALCZAF results but never the high JEOL numbers for the Z factors.....So, I have to go on to find out the final truth, hopefully  ;)
And, Brian, it would be great to have your code for a test.
Regards, Thomas