Questions about MAN background use

[BenjaminWade]

I have one and it's not super high resolution or super high count times (steps of 4 units, 4 sec/point), but I still can't see anything obvious in this scan on one of my TiO2?

Cheers

[Malcolm Roberts]

Here you go John... as requested. One of the more recent ones.......

[Probeman]

Hi Malc,
It would be really interesting to see how your TiO2 standard plots on this curve. Do you have a F ka MAN plot with TiO2?
John

[Probeman]

It would also be interesting to see how Ti metal plots up on these F Ka MAN curves, but it would be important that the Ti metal is freshly polished at least. The F Ka emission volume is very shallow, so the oxidation layer should be as thin as possible so the continuum absorption calculation is accurate.

[Probeman]

With regard to Ben Wade's MAN plots for F Ka on TAP and the TiO2 outlier, here are some more of my wandering thoughts.

1. The MACs for F Ka in TiO2 are quite large.  For F Ka in Ti the tables MACs (from CalcZAF) are:

MAC value for F Ka in Ti =   14588.35  (LINEMU   Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV)
MAC value for F Ka in Ti =   14540.00  (CITZMU   Heinrich (1966) and Henke and Ebisu (1974))
MAC value for F Ka in Ti =        .00  (MCMASTER McMaster (LLL, 1969) (modified by Rivers))
MAC value for F Ka in Ti =   14986.59  (MAC30    Heinrich (Fit to Goldstein tables, 1987))
MAC value for F Ka in Ti =        .00  (MACJTA   Armstrong (FRAME equations, 1992))
MAC value for F Ka in Ti =   14277.71  (FFAST    Chantler (NIST v 2.1, 2005))
MAC value for F Ka in Ti =   14500.00  (USERMAC  User Defined MAC Table)

and for F ka in O they are:

MAC value for F Ka in O =   12439.63  (LINEMU   Henke (LBL, 1985) < 10KeV / CITZMU > 10KeV)
MAC value for F Ka in O =   12390.00  (CITZMU   Heinrich (1966) and Henke and Ebisu (1974))
MAC value for F Ka in O =        .00  (MCMASTER McMaster (LLL, 1969) (modified by Rivers))
MAC value for F Ka in O =   11927.75  (MAC30    Heinrich (Fit to Goldstein tables, 1987))
MAC value for F Ka in O =        .00  (MACJTA   Armstrong (FRAME equations, 1992))
MAC value for F Ka in O =   11863.62  (FFAST    Chantler (NIST v 2.1, 2005))
MAC value for F Ka in O =   12400.00  (USERMAC  User Defined MAC Table)

I don't have Ben's MDB file handy at the university, but yesterday from home I tried selecting the lowest MAC table values (FFAST), and the MAN fit for TiO2 (#559) was still about the same amount over the trend line.  So it doesn't seem possible that the MAC could be off that much.

Interestingly if we look at the calculated MAN absorption corrections as seen here (from running PFE in DebugMode):

MAN fit data for Mg ka, SP4 TAP, 15 keV
     Std       J  MANSet    Npts   Z-bar     Cps  AbsCor
     504       1       1       1 14.3913 .715813 1.58141
     501       2       1       2 10.7106 .523931 1.49128
     541       3       1       3 12.0184 .548867 1.43226
     559       4       1       4 16.3937 .584618 1.83249   <- TiO2
     578       5       1       5 20.5879 .668368 2.41281
     701       6       1       6 10.7190 .618357 1.33443
     503       7       1       7 13.4430 .615176 1.54753
     549       8       1       8 6.12880 .349537 1.25008
     571       9       1       9 11.7470 .557961 1.40367
     575      10       1      10 10.6460 .638117 1.31164
     589      11       1      11 14.0000 .831370 1.09576
     594      12       1      12 4.00000 .280255 .964030
     602      13       1      13 27.0000 .713668 3.01841
     619      14       1      14 21.0000 .834364 1.82118
     514      15       1      15 26.6522 .592982 3.27371

we can see that the largest corrections are for F Ka in some of the other standards. So it could be the MAN continuum absorption correction, but why is TiO2 more of an outlier than the other standards with larger corrections?

Note: many years ago I attempted to apply a true continuum absorption correction using Myklebust's continuum expression, but I got worse regression results than just using the normal phi-rho-z bulk absorption correction...

[John Donovan]

I split off the rest of the discussion regarding this F Ka ROI mystery peak artifact on TAP crystals (and possibly related standards containing Ti) to a new topic:

http://probesoftware.com/smf/index.php?topic=992.0

This is because we suspect this mystery peak to be a diffraction artifact of some kind.  Another topic of interest could also be this one:

http://probesoftware.com/smf/index.php?topic=611.0

on JEOL H-type crystal artifacts, or this one on peak shape changes over time:

http://probesoftware.com/smf/index.php?topic=854.0

john

[JohnF]

There are times (like right now) where I have been using a MAN fit I created days ago, and there is no need to go thru revising it. Someone is asking me to show/prove that it as good as I say it is. However, I see no way where I can simply show the display. Nor is there any where where I can find a listing of which standards I ended up using for each element MAN fit, nor of the fit parameter.

Is there a feasible way that these plots could be stored somewhere? (There are many many Display options under the "Run" tab.) Likewise there are many List options under the same Run tab; might the MAN standard options be listed?   Or is all of that data volatile?

[John Donovan]

Hi John,
I don't see a problem with using the existing MAN plot dialog.  You don't have to "revise" anything, just click on each element to see the MAN plot for it, and optionally click the Copy to Clipboard button to capture the plot graphics to paste into a document or whatever.

If you accidentally change some assignments in the MAN dialog and don't want to have them saved, just click Cancel button instead of the OK button to exit.

Am I missing something?
john

[JohnF]

Roger.

[JohnF]

I am doing some quality control checking of MAN results at minor and trace el levels: Mg, Sr, Mn and Fe in carbonates (using defocused 20 micron beam). I have wavescan data to compare the MAN-predicted bkg counts with. Sr, Mn and Fe MAN numbers match nicely with the wavescan numbers. The particular sample which I am testing has a mean Z of 12.6.

From both wavescans and discrete background measurements on the sample (which has a very small distinct peak; backgrounds are clear), the background should be 12.5.

However, the MAN fitted background, using the continuum absorption correction, gives a background of 17, which doesn't seem correct. If I turn off the cont. abs. correction, there is a wonky curve but the value at a mean Z of 12.6 is closer to the actual measured background level.

(Note: conincidence that the carbonate Z is 12.6, and the actual back ground is 12.5 c/s/20nA)

Again all other 3 elements, Sr, Mn and Fe work great with the con. abs. corrected MAN values being what the wavescans show.

Could there be something weird going on for Mg?

MAN stds were acquired in normal acquisition mode (not TDI). Carbonates later were run in TDI.

Attached are 2 plots

[Probeman]

Hi John,
Both plots are correct.  But it is a little unintuitive, so good question!

The plotted (absorption corrected) MAN intensities in the Assign MAN Fits dialog are the "ideal" background intensities. They cannot be compared to actual measurements.  But by turning off the absorption correction in the MAN dialog, you are seeing the raw measured values, however which cannot be fitted together, because each MAN standard has different matrix physics.   But if the unknown matrix is the same as an individual MAN standard, then you can compare this "raw" intensity to off-peak measurements, as you observed. Please re-read the Donovan, et al. 2016 paper in Amer. Min for a complete explanation:

http://epmalab.uoregon.edu/publ/A%20new%20EPMA%20method%20for%20fast%20trace%20element%20analysis%20in%20simple%20matrices.pdf

In short, this is because each MAN standard is a different matrix and therefore needs to be corrected for the specific emission line individually before fitting.  Then once we have the equation of fit for these "ideal" intensities for the MAN standards, we can apply that fit to an actual sample after it is "de-corrected" for the actual absorption in the sample.

If you want to compare the calculated MAN background intensity with off-peak measurements, see the procedure here:

http://probesoftware.com/smf/index.php?topic=4.msg189#msg189

Then compare the line in the output labeled "UNBG:". Which are the MAN *or* off-peak intensities for the sample.
john

[Julien]

Hi John,

It is my understanding that if we do have a MAN correction curve for an element, and if we do have analyzed an element with 2-point background, it should be possible to switch between the 2-point background correction and the MAN. And even if it is not the case, we could use the 2-point background for determining a MAN background correction curve.

My problem is that - for testing purpose - I want to switch between the 2-points background and the MAN background, yet I can NOT change the background type in elements/cations window. The background field are all grayed out, and I cannot change a thing...



I do have checked the option "Use MAN correction for Off-peak measurement..." in menu Analysis, and I do have a correct set of MAN correction (the program indeed asked me to reset the MAN correction, which I did).





Maybe I'm doing something wrong? Note that at first, I was using the “shared background” in this run. To enable the MAN background, I did the following:

• REMOVE the shared background
• Activate the “Use MAN correction for off peak elements”
• Hit the “Clear All MAN assignments”
• Re-assigned the MAN fits.

Nonetheless, in each case (with shared bkg or with linear 2-pts bkg after resetting the MAN fit), the MAN option in elements/cations remain unavailable… Am I doing something wrong? Any help would be greatly appreciated!

Julien

[John Donovan]

Hi Julien,
I think you are basically doing it correctly.   You don't need to change anything in the Elements/Cations dialog. Those options are for the background *acquisition* type (we'll modify the description to make it more obvious!).

I don't quite understand how you are seeing the MAN curve fits if you acquired off-peak standards and the Use Off-Peak Elements for MAN Fits menu is unchecked.  Maybe you had it checked earlier at some point?

Anyway, see here for an explanation of using standards acquired using off-peak bgds, but for the MAN fit:

https://probesoftware.com/smf/index.php?topic=4.msg189#msg189

The steps to use MAN backgrounds based on your off-peak acquired standards, is to first check the Use Off-Peak Elements for MAN Fits menu and then assign the MAN fits.  This allows the program to use standards acquired with off-peak backgrounds, for the MAN assignments, by "throwing away" the off-peak measurements on those standards.

Next if your samples are acquired using MAN backgrounds you are done. But if your samples are off-peak, then you need to check the next menu down which is the Use MAN Correction for Off-Peak Elements menu. This will force the program to utilize MAN background corrections even if the sample (std or unk) data was acquired using off-peak backgrounds.

To get real fancy you can also check the Use Interpolated Off-Peaks for MAN Fit checkbox in the Analytical | Analysis Options dialog as described here:

https://probesoftware.com/smf/index.php?topic=987.0

With this method, first suggested by Ben Hanson at Corning, the program obtains the MAN background intensities by interpolating the off-peak measurements.  This option can be very useful when you want to use MAN backgrounds for faster acquisition (especially quant x-ray maps), but your standards are contaminated with traces of the element of interest, for example using MAN fits for O ka!

I hope this makes sense, but let me know if you are still having trouble.  Feel free to also send me your MDB file.
john

[BenjaminWade]

Hi John and all
My wish would be to be able to (post acquisition) mix and match elements with MAN and off-peak post acquisition rather than all one or the other... I am sure it probably wouldn't be simple to implement though...

Cheers

[John Donovan]

Hi John and all
My wish would be to be able to (post acquisition) mix and match elements with MAN and off-peak post acquisition rather than all one or the other... I am sure it probably wouldn't be simple to implement though...

Cheers

Hi Ben,
Yeah it would be more than a little bit of work, I'll have to think how it might be possible.   But you can always do what I do, which is decide which elements should be MAN and which elements should be off-peak *before* you acquire data!   
john