Author Topic: Light element MACs when there is an overlapping element  (Read 219 times)

wrigke

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Light element MACs when there is an overlapping element
« on: April 11, 2019, 12:51:34 pm »
I am trying to determine MACs for Cka in U using the approach outlined in the XMAC program of SAMx.  Unfortunately in UC, at higher voltages there is a U peak (N iv O iv)on the PC2 crystal that nearly completely obscures the Cka peak.  However, by measuring U on its usual crystal (PET or QTZ), I can know how much U is in the sample.  By knowing the U concentration in the sample, the program should be able to determine the size of the U peak (in cps/na) that must be obscuring the C peak and subtract it out.  The remaining counts should be those from CKa.
 
BUT……
 
1.   If the U obscures the C peak, I cannot empirically determine an APF, therefore I must use the integral.  Correct?
2.   In order to use the xMAC program, I need to know the background corrected Cka in cps/na in U without the added counts from U.  How do I find out the magnitude of the U overlap correction so that I know how much cps/na to remove from the C signal?  Is it available in the software?  Do you think this is the correct approach?

Thanks in advance for your thoughts!
Karen

Probeman

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Re: Light element MACs when there is an overlapping element
« Reply #1 on: April 12, 2019, 12:19:52 pm »
I am trying to determine MACs for Cka in U using the approach outlined in the XMAC program of SAMx.  Unfortunately in UC, at higher voltages there is a U peak (N iv O iv)on the PC2 crystal that nearly completely obscures the Cka peak.  However, by measuring U on its usual crystal (PET or QTZ), I can know how much U is in the sample.  By knowing the U concentration in the sample, the program should be able to determine the size of the U peak (in cps/na) that must be obscuring the C peak and subtract it out.  The remaining counts should be those from CKa.
 
BUT……
 
1.   If the U obscures the C peak, I cannot empirically determine an APF, therefore I must use the integral.  Correct?
2.   In order to use the xMAC program, I need to know the background corrected Cka in cps/na in U without the added counts from U.  How do I find out the magnitude of the U overlap correction so that I know how much cps/na to remove from the C signal?  Is it available in the software?  Do you think this is the correct approach?

Thanks in advance for your thoughts!
Karen

Hi Karen,
Wow, this is a tough one I must say.  I saw it yesterday when you posted it, but needed to think about it overnight. I think I have some solutions for you.

For those that don't know, the XMAC program is a small app distributed by SAMX based on code by Pouchou and Pichoir that allows the user to calculate MACs (mass absorption coefficients) from intensity measurements made over range of beam energies in a compound containing the emitting element and the absorbing element.  It works best for low energy emission lines.  For these low energy emission lines it generally produces MAC values that are quite accurate. For a list of some empirically determined MACs generated by this app, see the Empirical MACs menu in CalcZAF or Probe for EPMA. Here's an example:

https://probesoftware.com/smf/index.php?topic=667.msg4064#msg4064

Now as far as the interference of U on C Ka in determining the MAC, I think the solution is going to be that you'll have to measure both C Ka and U Ma quantitatively at each beam energy and specify the interference correction(s).  How does this help, well it's not generally known but if you specify interference corrections in Probe for EPMA, the correction for spectral interference occurs during the matrix correction quantitatvely, so in the end you have not only concentrations corrected for interferences, but *also* you'll have k-ratios corrected for interference as well!  See note below.

By the way, this is why acquiring thin film intensities in Probe for EPMA works so well for spectral interferences on thin film samples. The k-ratios exported into STRATAGem are *already* corrected for spectral interferences!

Now XMAC doesn't care what units the intensities are in, so you could just take the spectral interference corrected k-ratios from Probe for EPMA and utilize those intensities for the empirical determination of your MAC.  It might end up being an interative process because you might want to enter the empirical MAC determined from XMAC into PFE to improve the accuracy of the calculation.

On the APF question for changes in the carbon peak shape, I think you should just utilize the integrated intensities option in Probe for EPMA so that you won't need to use APF values at all.  See the option Use Integrated Intensities in the Elements/Cations dialog. Here's an example using integrating intensities on sulfur and also aggregating multiple spectrometers:

https://probesoftware.com/smf/index.php?topic=42.msg4932#msg4932

Note: I looked at the (default) NIST x-ray database and I don't see a uranium line near C Ka (between 40 and 50 angstroms) , though I do see a 2nd order O Ka line.  I believe you but in what table are you seeing the U line near carbon Ka?  Is this the modified xray.mdb that you and Philipp developed for PFE?
« Last Edit: April 12, 2019, 12:47:47 pm by Probeman »
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Mike Matthews

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Re: Light element MACs when there is an overlapping element
« Reply #2 on: April 13, 2019, 02:18:31 am »
I’m actually analysing C in U right at the moment and talked about this very interference problem at the AMAS symposium a couple of months ago. You can’t completely separate the C and U lines but you can reduce the degree of interference by using the 2nd order C Ka line on either an LDE1/PC1 or a Pb-stearate. This puts the line at the top end of the spectrometer range, where the resolution is better. The stearate has the highest resolution of the light element crystals, and almost completely separates the two peaks but the intensity is really lousy (<200th that of the LDE2/PC2). Both still need overlap correction (really easy to set up in PfE, thanks John!). I’m using the LDE1/PC1 as a compromise between level of correction and useable count rate (~20th that of LDE2/PC2). Thanks to Ben Buse for suggesting this method. As John says, the k-ratio values that PfE outputs include the overlap correction.

I have a sort of linked question though: The interfering U line is the N6-O4 at 0.286keV, with a relative intensity of 0.01% (Bearden, 1967), but there should also be a N6-O5 line at 0.294keV which Bearden lists with a relative intensity of 1% (i.e. 100 times bigger than the N6-O4 line), but I see no evidence of this peak. My working theory is that the O5 shell in U isn’t normally occupied so the line can’t be fluoresced and the 1% intensity in Bearden is just a default value when the actual intensity hasn’t been measured. However, my understanding of how shells are occupied is very limited and I might be completely misunderstanding the diagrams. Can anyone confirm or deny this hypothesis?

Mike

Mike Matthews

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Re: Light element MACs when there is an overlapping element
« Reply #3 on: April 14, 2019, 12:03:46 am »
OK, after discussions with Xavier, it looks like I am mistaken about the shell occupancies: For U the 5f shell is partially filled and this corresponds to the O6 and O7 levels (I was wrongly equating the 5f with the O4 level) so the N6-O5 transition should be possible. However, unlike Bearden, the Penelope database lists the intensity of this transition as 1/10th that of the N6-O4 which may explain why I haven't seen it. That does make more sense since why would Bearden list it if it wasn't a possible transition. I guess the 1% relative intensity is just a default value if the actual value isn't known. Since I have some DU in the probe at the moment I'll try a slow scan to see if I can tease this peak out of the background.

Mike

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Re: Light element MACs when there is an overlapping element
« Reply #4 on: April 14, 2019, 08:15:09 am »
Xavier Llovet responded to both Mike and I and said we could post his comments. Here they are:

Quote
Hi John, Mike:

I've checked the electronic configuration of U and is 5f3 6d1 7s2 so in principle the O4 and O5 levels (5d) are filled. Those that are partially filled are the 5f levels, which would correspond to O6 and O7 levels. So if I'm correct, both two N6-O5 and N6-O4 lines should exist.

The problem could be in the relative intensity reported by Bearden. For instance, according to the PENELOPE database, the N6-O4 line (with energy 289 eV) is 10 times more intense that the N6-O5 line (with energy 298 eV), just the opposite than Bearden's data! You can find this information in the U.mat file:

15 20  0  7.40479E-05  2.89740E+02
15 21  0  4.72978E-06  2.98070E+02

(the transition "15 20 0" would correspond to the N6-O4 line and the transition "15 21 0" to the N6-O5 line)

So perhaps this could explain what you're seeing?

Regards,
Xavier

The (modified) NIST x-ray database included with Probe for EPMA does include some N emission lines, but not all apparently. I guess we need a KLMN x-ray database!

Pd MZ2               43.3622  .285930  1.00000        ES 
Pd MZ1               43.3622  .285930  10.0000        ES 
Ne KB1      III      43.3814  .857410  .500000        JD 
Se SLB1``   V        43.4488  1.42680  .250000        JD 
Dy M2-N1    V        43.4610  1.42640  1.25000        JD 
Ni SLA3     III      43.4691  .855680  .500000        JD 
La MB       III      43.5016  .855040  45.0000        JD 
Bi N5-N6             43.5801  .284500  1.00000        ES 
Eu M4-O2    IV       43.5993  1.13750  .064000        JD 
Eu MA1      IV       43.6146  1.13710  64.0000        JD 
Ag MG       II       43.6422  .568190  16.0000        JD 
Eu MA2      IV       43.6492  1.13620  64.0000        JD 
Tm MZ1      IV       43.6607  1.13590  3.84000        JD 
Er M4-O2    V        43.6630  1.41980  .025000        JD 
Tl N4-N6             43.6707  .283910  1.00000        ES 
Tm MZ2      IV       43.6761  1.13550  .640000        JD 
Se LB1      V        43.6876  1.41900  9.71200        JD 
Ni LA2      III      43.7081  .851000  5.72500        JD 
Ni LA1      III      43.7081  .851000  50.0000        JD 
Mn Ln       II       43.7338  .567000  5.14300        JD 
Ga L2-N3    IV       43.7724  1.13300  .173000        JD 
Ce M2-N4    IV       43.8266  1.13160  5.12000        JD 
Ga SLB1``   IV       43.8421  1.13120  .640000        JD 
Ne KA1      III      43.8467  .848310  50.0000        JD 
Ne KA2      III      43.8467  .848310  25.0000        JD 
Ga LG5      IV       43.8886  1.13000  .141000        JD 
Tm M3-N1    V        43.9260  1.41130  .250000        JD 
Pr MG       IV       43.9938  1.12730  38.4000        JD 
C  KA1               44.0023  .281770  100.000        ES        <-- carbon emission
C  KA2               44.0023  .281770  50.0000        ES        <-- carbon emission
Er MA1      V        44.0039  1.40880  25.0000        JD 
Er MA2      V        44.0039  1.40880  25.0000        JD 
Cs M2-N1    III      44.0049  .845260  7.00000        JD 
Cs MZ1      II       44.0063  .563490  8.00000        JD 
Ga LB1      IV       44.0837  1.12500  10.6910        JD 
La M3-N1    III      44.1759  .841990  .650000        JD 
Pd M2-N4    II       44.2016  .561000  .800000        JD 
Gd MG       V        44.2205  1.40190  6.52500        JD 
Zr M3-N1             44.2789  .280010  1.00000        ES 
As Ll       IV       44.2805  1.12000  3.15500        JD 
Sm MZ2      III      44.4259  .837250  .500000        JD 
Ge LG3      V        44.4392  1.39500  .028000        JD 
Mn Ll       II       44.5991  .556000  10.6000        JD 
Se SLA4     V        44.6119  1.38960  .250000        JD 
La MA1      III      44.6414  .833210  50.0000        JD 
La MA2      III      44.6414  .833210  50.0000        JD 
Eu M3-N1    IV       44.6432  1.11090  .640000        JD 
Se SLA5     V        44.6569  1.38820  .250000        JD 
As LB4      V        44.6633  1.38800  .650000        JD 
As LB3      V        44.6633  1.38800  1.19200        JD 
Ho SMB2     V        44.6859  1.38730  .250000        JD 
Cu Ln       III      44.7068  .831990  1.37500        JD 
Kr Ll       V        44.7601  1.38500  1.12700        JD 
Ga SLA4     IV       44.7601  1.10800  .640000        JD 
Sm MZ1      III      44.7865  .830510  3.00000        JD 
Se SLA3     V        44.7924  1.38400  .250000        JD 
Zn LB4      IV       44.8005  1.10700  1.51000        JD 
Zn LB3      IV       44.8005  1.10700  .250000        JD 
Ru M4-O2             44.8021  .276740  .010000        ES 
Ga SLA5     IV       44.8086  1.10680  .640000        JD 
W  MZ1      V        44.8118  1.38340  .336000        JD 
Ho MB       V        44.8280  1.38290  14.8610        JD 
La M4-O2    III      44.8313  .829680  .050000        JD 
Sm M2-N4    V        44.8832  1.38120  .300000        JD 
Se LA2      V        44.9548  1.37900  2.85500        JD 
Se LA1      V        44.9548  1.37900  25.0000        JD 
W  MZ2      V        44.9679  1.37860  1.12800        JD 
Ga SLA3     IV       44.9956  1.10220  .640000        JD 
Pb N5-N6             45.0021  .275510  1.00000        ES 
Sm MB       IV       45.0815  1.10010  56.3200        JD 
I  MG       III      45.1064  .824620  10.0000        JD 
Ga LA2      IV       45.1677  1.09800  7.30900        JD 
Ga LA1      IV       45.1677  1.09800  64.0000        JD 
Sb M2-M4             45.2023  .274290  .010000        ES 
Hg N4-N6             45.2023  .274290  1.00000        ES 
Na SKB^4    IV       45.2584  1.09580  .640000        JD 
Tb M2-N1    V        45.3495  1.36700  1.25000        JD 
Te M2-N4    III      45.3511  .820170  .500000        JD 
Nd M2-N1    IV       45.3993  1.09240  2.56000        JD 
Er MZ1      IV       45.4867  1.09030  3.84000        JD 
Er MZ2      IV       45.5118  1.08970  .640000        JD 
Ho M4-O2    V        45.5728  1.36030  .025000        JD 
Er M3-N1    V        45.5996  1.35950  .250000        JD 
Sm MA1      IV       45.7173  1.08480  64.0000        JD 
Sm MA2      IV       45.7173  1.08480  64.0000        JD 
Sm M4-O2    IV       45.7216  1.08470  .064000        JD 
Cd M2-N1    II       45.8018  .541400  4.00000        JD 
Ho MA2      V        45.8085  1.35330  25.0000        JD 
Ho MA1      V        45.8085  1.35330  25.0000        JD 
Cu Ll       III      45.8639  .811000  2.07000        JD 
In M3-N1    II       45.9503  .539650  .800000        JD 

By the way, I also searched Philipp Poeml's modified replacement NIST x-ray database, which has additional emission lines for the actinide elements, and it doesn't have these N emission lines for U either.
« Last Edit: April 14, 2019, 08:43:11 am by Probeman »
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Mike Matthews

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Re: Light element MACs when there is an overlapping element
« Reply #5 on: April 14, 2019, 01:52:35 pm »
It did take some digging to work out what the overlapping peak was, none of the software tools showed any U lines in that region of the spectrum. We had to resort, as the late Douglas Adams put it, to twig-technology and dig out the hard copy x-ray tables.

wrigke

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Re: Light element MACs when there is an overlapping element
« Reply #6 on: April 15, 2019, 03:06:18 pm »
Thank you all for your suggestions.  I will let you know what I find out when I try these suggestions.

I do have a question about the overlapping line though.  My Bearden 1967 clearly describes the U line at 286 ev as "N4O4", not N6O4.  Is that a misprint in the article?

Karen

Mike Matthews

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Re: Light element MACs when there is an overlapping element
« Reply #7 on: April 24, 2019, 04:02:30 am »
Hi Karen,

Sorry for the delay in replying. I got my info from the NIST x-ray database which does quote Bearden 1967 as one of its sources, but this gives the line as N6-O4. Looks like there's been a transcription error somewhere. Does anyone have the big Cameca book of x-ray tables to hand to see what that one says is the U-line at 43.4 A, 0.286 keV?

Mike

Probeman

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Re: Light element MACs when there is an overlapping element
« Reply #8 on: April 24, 2019, 10:04:11 am »
Hi Karen,

Sorry for the delay in replying. I got my info from the NIST x-ray database which does quote Bearden 1967 as one of its sources, but this gives the line as N6-O4. Looks like there's been a transcription error somewhere. Does anyone have the big Cameca book of x-ray tables to hand to see what that one says is the U-line at 43.4 A, 0.286 keV?

Mike

I only have the BRGM "little book" which only goes down to the U M lines, but I do have a White and Johnson (2nd edition, May 1970) book which reports:

U N6-O4    0.286 KeV    43.29999 angstroms

OK, I also found my Bearden 1964 book which lists:

U N6-O4    0.286 KeV     43.6 angstroms  (literally NVI OIV, but if my Roman numerals are correct that's N6-O4) 
« Last Edit: April 24, 2019, 10:11:11 am by Probeman »
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