What exactly limits the accuracy of modern EPMA?
After some discussion with several colleagues and much consideration I have come to a few ideas on what is going on. I think there are several problems with improving accuracy in EPMA, partly consisting of unreliable naturally sourced standard materials, but also outmoded practices which no longer reflect improvements in modern hardware and software. I'd like to discuss these ideas in this topic starting with the use of what some of us refer to as "matrix" matched standards.
We usually speak of using "matrix" matched standards in order to minimize the magnitude of our matrix corrections when extrapolating from our standard to our unknown. But today's modern analytical matrix corrections are quite accurate as shown in many recent evaluations. Today's matrix corrections, even using relatively low energy emission lines, at relatively high beam energies, our modern matrix correction can yield highly accurate results even when they exceed 50% to 100% or more. Here are just a few recent examples:
https://smf.probesoftware.com/index.php?topic=1823.0
Ritchie, N. W., D. E. Newbury, and S. Leigh. "Breaking the 1% accuracy barrier in EPMA." Microscopy and Microanalysis 18.S2 (2012): 1006-1007.
So why do so many EPMA labs still think that so called naturally sourced "matrix" matched standards are necessary?
It's true that 30 years ago, matrix corrections were less accurate and at that time there may have been some justification for choosing a standard with a matrix somewhat similar to our unknown samples. Yes, we would not want to utilize a Si metal standard for analyzing Si in silicates, as there is a considerable peak shape/shift for Si Ka between these materials. And yes, there are a few "black holes" in the periodic table that may require a roughly similar matrix, e.g., Si Ka in Hf due to disagreement in mass absorption coefficients. But geological silicates and oxides are pretty well handled by modern matrix corrections.
So why not just use synthetic MgO as a primary standard for Mg Ka for ones silicate analyses? If we have a pure synthetic MgO, the composition should be well known, right? And it is readily available in kilogram quantities!
In fact, we suspect that our matrix corrections are not the main accuracy issue today. Instead, part of the problem is that in choosing these "matrix" matched standards, we have traditionally opted for natural materials which we now know are heterogeneous, inclusion filled and also of limited supply:
https://smf.probesoftware.com/index.php?topic=1415.0
As Gene Jarosewich once said of the Smithsonian geological standards: one should always take the average of 10 to 15 separate grains in order to get a standard measurement that accurately reflects the wet chemistry average. But let's be honest, does *anyone* actually do this in their probe labs?
To avoid these standard accuracy issues, we should instead be moving to high purity, synthetic minerals that are carefully characterized for purity, homogeneity, stoichiometry and are readily available in abundance and *globally* distributed. As is currently being done by Will Nachlas and the FIGMAS group with MAS support:
https://smf.probesoftware.com/index.php?topic=1415.msg10368;topicseen#msg10368
So why do some labs still insist on using these so called "matrix" matched standards even though we know there are better, high purity synthetic materials available today? See below for some possible explanations. But as Penny Wieser has demonstrated in her "Barometers Behaving Badly" paper, the problem extends beyond the use of heterogeneous and inclusion filled natural "standards":
(https://smf.probesoftware.com/gallery/395_18_11_21_11_28_07.png)
Wieser, Penny E., et al. "Barometers behaving badly I: assessing the influence of analytical and experimental uncertainty on clinopyroxene thermobarometry calculations at crustal conditions." Journal of Petrology 64.2 (2023): egac126.
There is something else that is not right about our EPMA WDS measurements!
We now suspect that in addition to the accuracy concerns of natural standards, the underlying problems with EPMA accuracy today primarily have to do with differences in the *count rate*, as measured on the instrument, between the standard and unknown. Therefore we propose that instead of calling these "matrix" matched standards, we call them "count rate" matched standards. Why do we think *count rate* matched is the more appropriate term?
1. Dead TimeMost WDS instruments are not well calibrated for dead time corrections, especially at count rates now commonly seen with modern instruments using large area crystals. This matters when using high purity synthetic standard materials because if you go from an unknown with a count rate that is different than the primary standard, the quantitative accuracy will depend on the accuracy of the dead time correction, even at moderate beam currents. Because when measuring major elements on modern instruments with large area Bragg crystals, one can easily obtain dead time corrections of 10% to 30% or more, even at moderate beam currents.
Without an accurate (logarithmic) dead time calibration as described here:
https://smf.probesoftware.com/index.php?topic=1466.msg11102#msg11102
Donovan, John J., et al. "a new method for dead time calibration and a new expression for correction of WDS Intensities for microanalysis." Microscopy and Microanalysis 29.3 (2023): 1096-1110.
one will be forced to utilize these "count rate" matched natural standards with their documented heterogeneity, Even Si Ka on a normal TAP Bragg crystal can yield significant count rates at moderate beam currents, due to its low sin theta and hence larger subtended angle.
And what about quantitative mapping at high beam currents? Having a linear PHA response and an accurate dead time correction becomes essential for quantitative mapping accuracy. In fact, with properly adjusted PHAs and an accurate dead time correction, we can now perform quantitative mapping at high beam currents using WDS:
https://smf.probesoftware.com/index.php?topic=1466.msg11629#msg11629
Donovan, John J., et al. "Quantitative WDS compositional mapping using the electron microprobe." American Mineralogist: Journal of Earth and Planetary Materials 106.11 (2021): 1717-1735.
https://epmalab.uoregon.edu/pdfs/Donovan_2021_Amer_Min_2021-7739.pdf
2. PHA Tuning:We also believe that PHA tuning is being performed improperly by some EPMA labs. First, some EPMA labs are tuning their PHAs on their unknown sample rather than the primary standard. Why does this matter? Because PHAs are sensitive to count rate.
Therefore tuning ones PHA by centering the PHA peak in the PHA distribution (e.g., 4v on a JEOL instrument) with the baseline level set below the PHA peak and setting the PHA window above the PHA peak (and using differential PHA mode) will not yield quantitative results when the count rates between the standard and unknown are significantly different, as will often be the case with modern EPMA instruments using large area crystals with correspondingly higher count rates.
Specifically, the problem with this PHA tuning method is, if we go to another material, for instance ones primary standard, containing a different concentration of the element and therefore likely a higher count rate, the peak will shift to the left (possibly intersecting the baseline level) due to more pulse height depression.
We believe this is why some EPMA labs have found it necessary to use a standard that is "matrix" matched to their unknown. Because when they look for a standard that is "matrix" matched and therefore usually of a similar composition, they are really "count rate" matching to their unknown. In other words, due to improper adjustment of their PHA settings, they obtain inaccurate results when extrapolating, from well characterized and homogeneous pure synthetic MgO or Al2O3 or Fe2O3 materials, to their natural unknowns usually with lower count rates. Essentially they are "count rate" matching to avoid pulse height depression effects, rather than actually "matrix" matching to avoid large matrix corrections.
In addition, because these natural materials tend to be heterogeneous and of uncertain accuracy, as described above, that introduces further inaccuracy.
How can we fix this PHA tuning problem? Well the first clue to this was when SEM Geologist suggested that we should not be running in "Differential" mode generally, and instead run the PHAs in "Integral" mode, that is, without a PHA window level filter. This is particularly important for lower energy emission lines on TAP and LDE Bragg crystals:
https://smf.probesoftware.com/index.php?topic=1466.msg11549;topicseen#msg11549
Yes, differential mode can help with some higher Bragg order interferences, but it doesn't help at all with *same* Bragg order interferences, and only partially with higher Bragg order interferences. In fact there are only a few rare spectral interference situations I can think of where differential mode might help, such as Na Ka 2nd Bragg order interfering when measuring trace oxygen, because it's difficult to find a standard for the interference correction that contains sodium but no oxygen.
Otherwise it makes much more sense to tune your PHAs to obtain a linear response in count rate over a large range of count rate, and then correct for any spectral interferences using the quantitative interference correction in software:
Donovan, John J., Donald A. Snyder, and Mark L. Rivers. "An improved interference correction for trace element analysis." Proceedings of the Annual Meeting-Electron Microscopy Society of America. San Francisco Press, 1992.
That means adjusting your PHAs on a material with the highest count rate you will be observing, which is usually the primary standard for that element, at the highest beam current you will be utilizing. Then adjust the PHA peak position using the gain (Cameca) or bias (JEOL), until the PHA peak is *completely* above the baselines level. This is critically important as we will see, for obtaining a linear response over a range of count rates.
And utilize PHA Integral mode! That way, when you move to a material with a lower count rate, the PHA peak will shift to the right, and in Integral mode all the photons will still be counted, even if the PHA peak is graphically "cut off" to the right:
https://smf.probesoftware.com/index.php?topic=1466.msg11450;topicseen#msg11450
At "normal" beam currents this graphical "cutting off" of the PHA peak on the right will usually only occur with very low energy emission lines such as O Ka or N Ka, etc. Though when attempting to acquire "constant" k-ratios from low beam currents to 200 nA or more for the dead time calibration (see above), one can see this "cutoff" effect even for Si Ka as shown in the link above.
So even though it appears that the PHA peak is "cut off" in the PHA plots, all photons to the right will still be counted in Integral mode.
So it is critical for all emission lines to have their PHA peak adjusted so the PHA peak is *completely* above the baseline level at the highest count rate that is expected to occur, and to always run ones analyses in integral PHA mode!
Summary:First we need to have our WDS spectrometers carefully aligned mechanically. See here for the Bragg Order k-ratio tests to check spectrometer alignment:
https://smf.probesoftware.com/index.php?topic=1739.0
Your instrument engineer may need to perform these alignments, but check using the Bragg Order k-ratio tests linked above:
Then once your dead time constants are carefully calibrated using the Constant K-ratio method, and your PHAs are properly tuned and using *integral* PHA mode as described above, you can expect excellent accuracy even when extrapolating from synthetic MgO and Al2O3 to MgAl2O4 at 20 keV and 30 nA (8 um):
TYPE: ANAL ANAL ANAL
BGDS: EXP LIN LIN
TIME: 60.00 60.00 60.00
BEAM: 30.06 30.06 30.06
ELEM: O Mg Al SUM
126 44.826 17.098 37.646 99.570
127 44.779 17.113 37.549 99.441
128 44.894 17.080 38.119 100.093
129 44.740 17.109 37.652 99.501
130 44.798 17.143 37.533 99.473
AVER: 44.807 17.108 37.700 99.616
SDEV: .057 .023 .241 .271
SERR: .026 .010 .108
%RSD: .13 .13 .64
PUBL: 44.985 17.084 37.931 100.000
%VAR: -.40 .14 -.61
DIFF: -.178 .025 -.231
STDS: 3012 3012 3013
STKF: .2100 .4274 .4047
STCT: 256.16 1936.93 925.50
UNKF: .2176 .1172 .2239
UNCT: 265.44 531.14 511.96
UNBG: 1.55 2.02 .79
ZCOR: 2.0592 1.4597 1.6842
KRAW: 1.0362 .2742 .5532
PKBG: 172.61 264.22 648.77
And here's a more recent example extrapolating from synthetic MgO and SiO2 to synthetic Mg2SiO4 also at 20 keV and 30 nA (10 um):
St 273 Set 2 Mg2SiO4 (magnesium olivine) synthetic, Results in Elemental Weight Percents
ELEM: O Si Mg
TYPE: ANAL ANAL ANAL
BGDS: LIN LIN LIN
TIME: 60.00 60.00 60.00
BEAM: 29.90 29.90 29.90
ELEM: O Si Mg SUM
136 45.716 19.786 34.595 100.097
137 45.822 19.800 34.557 100.180
138 45.798 19.752 34.578 100.128
139 45.776 19.769 34.551 100.095
140 45.945 19.766 34.499 100.210
AVER: 45.811 19.775 34.556 100.142
SDEV: .084 .019 .036 .051
SERR: .038 .008 .016
%RSD: .18 .10 .10
PUBL: 45.486 19.960 34.554 100.000
%VAR: .72 -.93 .01
DIFF: .325 -.185 .002
STDS: 12 14 12
STKF: .2084 .3904 .4269
STCT: 254.13 2242.56 815.27
UNKF: .2158 .1217 .2295
UNCT: 263.14 699.14 438.19
UNBG: 2.54 3.23 .64
ZCOR: 2.1225 1.6248 1.5060
KRAW: 1.0355 .3118 .5375
PKBG: 104.57 217.60 688.52
Note the %VAR and ZCOR values. These are significant matrix corrections, yet still better than 1% relative accuracy at 20 keV! The problem is not our matrix corrections, the problem is our natural "count rate" matched standard materials along with our dead time calibrations and PHA tuning.
If you want to focus the beam more, use the TDI correction. It works! With modern FEG instruments with highly focussed beams, the TDI correction integrated with the quantitative matrix correction is more important than ever:
https://smf.probesoftware.com/index.php?topic=11.msg5910#msg5910
These are simple and easy tests to perform. What do you think of all this? Do you care about EPMA accuracy?
Run some tests as seen in the FIGMAS challenge topic linked below and let us know what quantitative accuracy you obtain with a properly calibrated instrument using pure oxide standards:
https://smf.probesoftware.com/index.php?topic=1823.0
Andrew Ducharme found this review article which I had looked at when it came out, and the section on PHA tuning (which I did not note at the time!) illustrates the issues with counting electronics linearity which we discuss in the above post (yeah, it's long but we think worth reading!).
Here's the first screen shot from the pdf:
(https://smf.probesoftware.com/gallery/395_14_03_26_3_32_08.png)
and the second:
(https://smf.probesoftware.com/gallery/395_14_03_26_3_32_24.png)
Llovet, Xavier, et al. "Reprint of: Electron probe microanalysis: A review of recent developments and applications in materials science and engineering." Progress in Materials Science 120 (2021): 100818.
I would comment that yes, if we do not tune our PHA settings using the highest count rates that we expect to measure, then by going to a higher count rate on our pure element or pure oxide standard, we will experience pulse height depression and therefore lose counts as the PHA peak shifts to the left as the PHA peak is filtered by the baseline level.
However, if I read correctly, the authors are not correct that the use of differential mode with a PHA window level will make this situation worse because it is only at lower count rates that the PHA peak will shift to the right!
The use of differential mode will only introduce non-linearity in the counting electronics when tuning the PHA on a on a high count rate standard, and then moving to a low count rate unknown, where the PHA peak will shift to the right.
As stated in the previous post, instead, the best procedure is to NOT use differential mode (that is use Integral mode), and to tune your PHA peak at the highest count rate you expect to measure, and make sure that the PHA peak is fully and completely above the baseline level at that high count count rate.
The suggestion to utilize lower beam currents on the high count rate standard and higher beam currents on the lower unknown is not wrong, but then relies on the linearity of ones picoammeter, which can be problematic:
https://smf.probesoftware.com/index.php?topic=1466.msg11324#msg11324
The bottom line is that one can obtain
a fully linear response from ones counting electronics by tuning the PHA at the highest intensity one expects to measure, and leaving the PHA in Integral mode. As one goes to lower count rates, say on ones unknown, yes, the PHA peak will shift to the right, but in Integral mode all the photons will be counted even though they appear to be "cut off" graphically!
Here are some PHA plots from our quantitative runs where we obtained ~0.5% accuracy starting with Mg Ka (note Mg Ka in MgO = ~60 kcps and in MgAl2O4 = ~16 kcps. So just a bit of a count rate difference!
(https://smf.probesoftware.com/gallery/395_14_03_26_3_52_28.png)
And Al Ka:
(https://smf.probesoftware.com/gallery/395_14_03_26_3_52_48.png)
And O Ka:
(https://smf.probesoftware.com/gallery/395_14_03_26_3_53_06.png)
And here is the quant at analysis at 25 keV:
St 3100 Set 3 MgAl2O4 FIGMAS, Results in Elemental Weight Percents
ELEM: O Mg Al
TYPE: ANAL ANAL ANAL
BGDS: EXP LIN LIN
TIME: 60.00 60.00 60.00
BEAM: 30.19 30.19 30.19
ELEM: O Mg Al SUM
141 45.071 17.156 37.426 99.653
142 45.065 17.161 37.576 99.802
143 45.192 17.182 37.607 99.981
144 45.034 17.207 37.353 99.594
145 45.213 17.198 37.403 99.815
AVER: 45.115 17.181 37.473 99.769
SDEV: .082 .022 .112 .152
SERR: .036 .010 .050
%RSD: .18 .13 .30
PUBL: 44.985 17.084 37.931 100.000
%VAR: .29 .57 -1.21
DIFF: .130 .097 -.458
STDS: 3012 3012 3013
STKF: .1793 .3807 .3710
STCT: 216.43 2019.18 1028.68
UNKF: .1851 .1027 .1882
UNCT: 223.40 544.84 521.76
UNBG: 1.44 1.98 .77
ZCOR: 2.4376 1.6725 1.9916
KRAW: 1.0322 .2698 .5072
PKBG: 156.40 275.78 678.72
Oxygen and magnesium accuracy is within ~0.5% relative! Aluminum is a bit worse, but again we suspect an alignment problem on that spectrometer because when running Al Ka on spectrometer 1 we get ~0.5% accuracy as demonstrated here:
https://smf.probesoftware.com/index.php?topic=1823.msg13917#msg13917
Quote from: Probeman on March 14, 2026, 04:04:27 PMThe bottom line is that one can obtain a fully linear response from ones counting electronics by tuning the PHA at the highest intensity one expects to measure, and leaving the PHA in Integral mode. As one goes to lower count rates, say on ones unknown, yes, the PHA peak will shift to the right, but in Integral mode all the photons will be counted even though they appear to be "cut off" graphically!
This last weekend Andrew Ducharme found in the Cameca Reference guide that in Integral PHA mode, the pulse processing electronics will include all photons up to 10v even though the software only displays photons up to 5 v.
Does anyone know what voltage the JEOL PHA electronics will count up to when in Integral mode?
Quote from: Probeman on March 16, 2026, 10:34:05 AMThis last weekend Andrew Ducharme found in the Cameca Reference guide that in Integral PHA mode, the pulse processing electronics will include all photons up to 10v even though the software only displays photons up to 5 v.
Just to add to this: there is nothing larger than 10V at measurement as any pulse which would be larger than 10V is clipped-down to 10V before being digitized. Counters on Cameca EPMA's are also capable to sense some cosmic radiation (very energetic events, recognizable as very steep pulses clipped at max already at pulse shapping stage) - they make that random background noise (2-10cps) in WDS ratemeters when beam is off.
Quote from: sem-geologist on March 16, 2026, 03:56:35 PMJust to add to this: there is nothing larger than 10V at measurement as any pulse which would be larger than 10V is clipped-down to 10V before being digitized.
So you are saying, that photons (or other particles)
that produce pulses with a voltage greater than 10v would still be counted? I wonder why Cameca bothered to mention the 10v limit in their reference manual?
Would that also be true for JEOL counting electronics? I'm guessing yes, because John Armstrong once mentioned seeing cosmic ray counts when the beam is off on his JEOL instrument.
To understand what "clipping" is and to not write lengthy explanations (which I tend to overdo) I just forward to wikipedia:
https://en.wikipedia.org/wiki/Clipping_(signal_processing) (https://en.wikipedia.org/wiki/Clipping_(signal_processing))
So in older Cameca systems (which I believe those reference manuals could be referencing to) were clipping signals between 0.56V and 10V as ADC was 10V capable. If you have new gen WDS electronics those actually clip signal to 0.56V and 5V range as more modern ADC is 5V.
Practically any analog signals when being fed to modern ADC's needs to be protectively clipped to not over-exceed ADC input voltage limits. I am quite convinced Jeol probe needs to do signal clipping too, even without taking a glimpse to their actual design. They probably clip lower bound differently, where Cameca use diode in series in signal path, and Jeol probably just drains negative part of signal to GND.
Thus yes - be it raw photon have 10keV or 100keV or 1MeV or 1GeV - if it had produced any Townsend avalanche in GFCP, and counting electronics is not in enforced dead-time time gap, it will be registered at clipped upper value of ADC input range in PHA. To clarify even further: all above listed high energy photons will be registered as same 10V height pulse on 10V ADC, or as 5V pulse on 5V ADC. (If bias and gain is set to project Photon energies from 0keV to 10keV into 0V to 10V height pulses).
Quote from: sem-geologist on March 17, 2026, 05:40:07 AMThus yes - be it raw photon have 10keV or 100keV or 1MeV or 1GeV - if it had produced any Townsend avalanche in GFCP, and counting electronics is not in enforced dead-time time gap, it will be registered at clipped upper value of ADC input range in PHA. To clarify even further: all above listed high energy photons will be registered as same 10V height pulse on 10V ADC, or as 5V pulse on 5V ADC. (If bias and gain is set to project Photon energies from 0keV to 10keV into 0V to 10V height pulses).
OK, thanks.
Being limited to 5 V on modern electronics seems quite bad for WDS? Differential mode windows of 5-5.5 V (stretching b/w ~0.5-6 V) aren't uncommon, even if I don't think you should use them. Clipping at 5 V could then be quite negative.
On older electronics, how many counts should we expect at 10 V? Would it be worth using "differential mode" with a normal baseline and a high window edge at 9.9 or 9.95 V? I doubt it, since integral mode measurements have not been noticeably worsened by them already. We could measure the effect though by measuring counts in integral and this proposed gigantic differential mode.
Quote from: aducharme on March 17, 2026, 01:39:31 PMBeing limited to 5 V on modern electronics seems quite bad for WDS? Differential mode windows of 5-5.5 V (stretching b/w ~0.5-6 V) aren't uncommon, even if I don't think you should use them. Clipping at 5 V could then be quite negative.
The big elephant in the room - component design during last decades had changed, and it changed IMHO to the right direction actually. You had to have plenty of room for Analog signals for them to be "immune" to digital noise around. While chips from 70ies, 80ies and early 90ies were slow and their digital transitions were slow - their emission of noise into analog signal also was moderate. 0-10V dynamic range or even -10 to +10V range was very common then for analog lines, In those times it was a brute force attempt to counteract a completely shitty design of PCBs with star-ground nonsense or other woodoo engineering practices which had then not bite back severely, but would had coupled some perceivable noise to analog lines if they would have lower dynamic range (i.e. 0-5V). Fortunately modern PCB design went in the right direction and started ditching these outdated terrible designs, starting to use full ground plains multi-layer PCB's, high density designs, surface mounted parts, Finally whole PCB can be designed with everything having controlled impedance and controlled noise level. Digital chips got much faster where state transition if designed poorly can emit and couple into everything around, including analog traces. Fortunately majority of electronic producers were forced by EMC/EMI regulations to adapt and follow good design practices and ditch bad ones those one which had not adapted went bancrupt and dropped from the market). That made these very wide range ADC's irrelevant. It is really hard to find any new ADC with such range, and there are only some few slow ADC's for some legacy industrial system interaction. Even 0-5V ADC market is starting to shrink at the moment, as proper designed PCB can have lesser dynamic range of analog signal and still be able to get noise free. It is not how big dynamic range is, but how many bits we can quantitize to so that least significant bit would still be above the noise. That is modern analog signals can be quantitized with 24bit ADC's, where ancient ADC from 70'ies would do 12 - 14bit, sometimes even 16, but those last two most significant bits would be noisy. Common and Fast ADC's had 8 bit resolution. And that is what old Cameca hardware used: 0-10V ADC with 8 bits. interestingly it showed in PHA only up to 5.5V Why it was hiding the rest?
New gen multilayer PCB use 5V ADC, also 8-bit. Practically it is the same amount of information as old design. Nothing more and nothing less.
QuoteOn older electronics, how many counts should we expect at 10 V? Would it be worth using "differential mode" with a normal baseline and a high window edge at 9.9 or 9.95 V? I doubt it, since integral mode measurements have not been noticeably worsened by them already. We could measure the effect though by measuring counts in integral and this proposed gigantic differential mode.
at 10V? I would expect same amount of counts as on modern 5V., which in both cases are not reported to PHA graph by firmware as would make steep single measurement channel-wide anomalously looking peak. If you are asking about the measurements I did those, and there is difference with wide diff and integral when peak of PHA distribution highly escape the right side. I encourage to do them on your own, you will see on your own the difference. The integral mode actually does not care about height of the pulse, as integral count is triggered by raising edge of pulse. Althought Cameca hardware do both measurement simultaniously despite selected mode and even return both with library when asking for counts.
But in my opnion new generation of WDS card have lesser bottleneck and If I could I would change old hardware to new on our old SX100. To put more fire into oil (or to put the bag into the cat :) ) I should clarify why. You see this 10V ADC is shared between 3 spectrometer! (1,2,3 spec use one ADC, and 4 and 5th spectrometer use second ADC). On newer hardware every spectrometer have its own ADC. Althought thats not whole picture... ADC's needs to wait for its turn to report the measurement results, as all 5 of them use same digital bus. But so far I could not find that it would influence one spectrometer, if other spectrometer have small or high count rates. On old hardware... well they have some clear additional dead time if other spectrometer is having very high count rates as they need to share ADC's. New generation WDS boards is one of upgrade worth every penny. Other cards of new generation are not so critical, or I would even say could be worse.
P.S. clipping is affecting pulse height, not count rate.
Quote from: sem-geologist on March 17, 2026, 03:17:18 PMthere is difference with wide diff and integral when peak of PHA distribution highly escape the right side
Yes, you're describing a flipped version of pulse height depression ruining a measurement. I was curious about this
Quote from: sem-geologist on March 17, 2026, 05:40:07 AMbe it raw photon have 10keV or 100keV or 1MeV or 1GeV - if it had produced any Townsend avalanche in GFCP, and counting electronics is not in enforced dead-time time gap, it will be registered at clipped upper value of ADC input range in PHA
and how many counts you would expect to exist at 5 V/10 V (depending on age of electronics) in the case where the PHA is properly set up. In other words, do cosmic rays and other high energy artifacts (if any exist) alone create a measurable amount of counts?
Quote from: sem-geologist on March 17, 2026, 03:17:18 PMYou see this 10V ADC is shared between 3 spectrometer
lol. Obviously the design has worked well enough, but it is a kludge that I'm surprised to see. If new generation WDS boards are worth every penny, are current dead-time corrections, built to work on any microprobe, inaccurate on these ADC-sharing instruments?
Ok, You made me start doubt myself for a moment.
Quote from: aducharme on March 17, 2026, 04:52:20 PMQuote from: sem-geologist on March 17, 2026, 03:17:18 PMthere is difference with wide diff and integral when peak of PHA distribution highly escape the right side
Yes, you're describing a flipped version of pulse height depression ruining a measurement. I was curious about this
To begin with there clearly is few peculiar things going: PHA graph does not report last few channels. And I also am not sure if we can set diff mode window to include the last channel. Graphically in peaksight if we move the the window by hand, be it old peaksight or new peaksight sofware, it pushes window back. The only way to select the higher bound as far as possible to the right is using text field and entering large number, it will then enter maximum possible value (i.e. on SX100 with older WDS card and peaksight 5.1; if base line is 560mV it can set 4999mV as window, which would make the right position of it be at 5.559mV. So, does it include last channel or not? I believe on both of systems (old and new) it does not include the last channel and Cameca libs and software does not allow to select the window wide enought to include last channel. But my memory could be wrong. If you have time please repeat that experiment.
Quote from: aducharme on March 17, 2026, 04:52:20 PMQuote from: sem-geologist on March 17, 2026, 05:40:07 AMbe it raw photon have 10keV or 100keV or 1MeV or 1GeV - if it had produced any Townsend avalanche in GFCP, and counting electronics is not in enforced dead-time time gap, it will be registered at clipped upper value of ADC input range in PHA
and how many counts you would expect to exist at 5 V/10 V (depending on age of electronics) in the case where the PHA is properly set up. In other words, do cosmic rays and other high energy artifacts (if any exist) alone create a measurable amount of counts?
cosmic rays do in casual conditions about 2 to 10 cps. Maybe there are higher fluctuations depending from sun cycle - I don't know, but if we do normally thousands of counts per second - that is at most 0.02 to 0.1%, and as it influence both, peak and background measurement it is practically removed. Same would apply for other external noise which influence both peak and background measurements the same. However there could be like 50% or even more in the last channel, when we set high gain and shift the distribution to overflow the right edge, and if we loose those counts by using diff - we loose a lot.
One of the key problems when tailoring the PHA for specific diff mode at moderate count rate is relying on setting the PHA only for peak position at moderate count rate. The background position which naturally would have much less counts and would have the PHA distribution more to the right and would escape partly the set narrow window. This is how it is easy to fall into the fallacy that PHA narrow window can significantly increase the peak/bkgd ratio of the measurement (I can't remember the exact papers on this, but there are at least few of them spreading such brilliant wisdom). No - it absolutely does not, as PHA distribution at background position would be shifted to the right and would miss partly the narrow PHA window and thus produce much lower background measurement compared to integer mode measurement, making peak/pkg look in the number artificially better, but missing the point that result is biased.
There is one exception where narrow window could work - if you can manage to make PHA distribution stand in the place (not shift) for counting rate range which includes target peak and background. That is doable only on Cameca hardware to some extent as those have both fine grained gain and bias, and I believe it is unachievable on Jeol hardware as they have only bias fine grained, but the gain is very course grained. There is small complications also as new dead-time calibration proposed by probeman is tailored for integral mode. The problem with narrow window (in case if achieving PHA with no shift) is the pulse pile up, which will make a deficit of counts inside the window with growing count rate. It needs then different dead time model. So efficiently such the common dead time mode is applicable for diff only at low – moderately low count rates, before "photon coincidences" rise in significant numbers. I use integral mode in 99.9% of cases, and use narrow diff window only for Pb Ma in geochronology applications with modified bias and gain for no PHA shift (remember you need to do also high concentration standards right with narrow PHA window). And I guess I would use just integer mode also there if we would use ProbeforSoftware, as PHA can shift with changing weather... I use PHA filtering there due to OEM Peaksight weakness in circular interference corrections. The Pros of diff window in that single case overcomes its numerous Cons.
Quote from: aducharme on March 17, 2026, 04:52:20 PMQuote from: sem-geologist on March 17, 2026, 03:17:18 PMYou see this 10V ADC is shared between 3 spectrometer
lol. Obviously the design has worked well enough, but it is a kludge that I'm surprised to see. If new generation WDS boards are worth every penny, are current dead-time corrections, built to work on any microprobe, inaccurate on these ADC-sharing instruments?
It actually works really great if knowing its weaknesses. On our old SX100 (with old WDS boards) we try to not allow any of our measurement to go over 15kcps, where clearly unlinearities starts to show up. Using peaksight is a limiting factor due to no ability to change dead time constants, maybe if we would use Probe Software we could do the calibration of deadtimes better and the upper reliable boundary clearly would grow up. We utilize multi conditions a lot to overcome the limitations. Both our probes had produced k-ratios for original FIGMAS tests within 0.5% boundary - that is not bad at all (our mount is #1-14). Also those two ADC's contains separate buses to the FPGA's, thus works in parallel, and Cameca tends to distribute out high intensity capable spectrometer connections across them. In our case the effect is very faint, as our first 3 spectrometers have small XTALS, and only 4th have large crystals capable to produce high count rates. To make 3 small XTALS to produce some super intensive counts to get real clue I had to manually set C1 C2 to make some insanely strong beam (if my memory not fails me around 3000nA). Thus I am not tearing my shirt off to get a new card as this one works correctly if staying within its limits. But if there would be an opportunity I would grab a new gen card for that without any hesitations.
Quote from: sem-geologist on March 18, 2026, 04:14:57 AMIf you have time please repeat that experiment.
No promises but I will try to do so this weekend.
Quote from: sem-geologist on March 18, 2026, 04:14:57 AMOne of the key problems when tailoring the PHA for specific diff mode
John and I completely agree with you. John has taken to referring to this approach to PHA calibration as "count-matching" (as opposed to matrix matching).
Quote from: sem-geologist on March 18, 2026, 04:14:57 AMAnd I guess I would use just integer mode also there if we would use ProbeforSoftware, as PHA can shift with changing weather
You know, I think integral mode is more robust to barometric pressure changes than differential mode. One of the impacts of lowering pressure is shifting the pulse to higher voltages. Llovet et al.'s 2021 review paper includes this plot showing the effect:
(https://smf.probesoftware.com/gallery/3292_18_03_26_9_38_37.png)
With a reasonable baseline, integral mode would not lose counts from shifts due barometric pressure, but differential mode would. It looks like there would still be an effect from the change in pulse shape, but I have no idea how that affects what the instrument reports when actually performing WDS.
I never had seen such a huge shift in PHA depending from weather on Cameca hardware - maybe it have something to do with bubblers which partially would prevent back stream of oxygen and water vapor?
Below I reattach my achieved fixed PHA up to 50kcps for high pressure spectrometers.
First, The initial shift review when relying on Automatic PHA setup:
(https://smf.probesoftware.com/gallery/1607_05_05_22_8_00_50.bmp)
After reducing bias (gas amplification) that reduces average load on feedback capacitor of preamplifier (makes it more empty than charged), which (skipping all important and lengthy details) delays the type I PHA shift. Type II shifting as we see still kicks in when going above 50 kcps due to increase of photon coincidence (again, this is gross oversimplification):
(https://smf.probesoftware.com/gallery/1607_05_05_22_8_05_38.bmp)
So practically staying bellow 15 kcps, diff mode on high pressure spectrometers can be used after reducing bias and increasing the gain. The range limitations are good enough for good calibration of well behaved Pb standard, and trace analysis at high current.
But as I said, that is the only case where I use diff mode and only with reduced bias and increased gain.
Quote from: sem-geologist on March 19, 2026, 04:18:32 AMI never had seen such a huge shift in PHA depending from weather on Cameca hardware - maybe it have something to do with bubblers which partially would prevent back stream of oxygen and water vapor?
It's difficult to compare, but we had this plot from Brian Joy back in 2022:
https://smf.probesoftware.com/index.php?topic=1109.msg10889#msg10889
I would be interested in seeing PHA scans from 10-30 nA up to several hundred nA on some large TAP/PET crystals.
For example as shown here:
https://smf.probesoftware.com/index.php?topic=1475.msg11330#msg11330
And separately, with the PHA peak fully above the baseline and in integral mode, do you see the same count rate as the gain is increased and the PHA peak is shifted to the right, even when it is cut off graphically? As shown here:
https://smf.probesoftware.com/index.php?topic=1475.msg11343#msg11343
Quote from: Probeman on March 19, 2026, 07:34:48 AMAnd separately, with the PHA peak fully above the baseline and in integral mode, do you see the same count rate as the gain is increased and the PHA peak is shifted to the right, even when it is cut off graphically? As shown here:
https://smf.probesoftware.com/index.php?topic=1475.msg11343#msg11343
As far I remember I looked into that – it does not influence that aspect. Indeed, the contrary (increasing bias, and reducing gain) could increase count loss at high count rates. As it would saturate C.S.P. and it could start introducing additional dead time there (which in normal conditions is dead-time free).
Albeit there is a limit how far bias can be lowered to still get same count rate, for high pressure counters the plato (where count rate is staying the same) is down to 1600V (it also very depends from X-ray energy), but I never set it this low, I set it rather ~1700V from commonly default auto set ~1830V (by peaksight). Why count rate starts to drop after going below ~1600V? (choose one/or both of reasons) a) as effective field around the anode in GFPC starts to be smaller than focused diffracted beam b) field is too weak to consistently produce Townsend avalanche from every X-ray produced photoelectron, and electrons are either reconnected to positive ions, or drifts without
amplification to the anode where they are collected, but because no amplification they are invisible hidden in the noise of the anode.
If you ever looked to this and similar scheme (from wikipedia):
(https://upload.wikimedia.org/wikipedia/commons/f/f7/Detector_regions.gif)
The X axis on that scheme is bias voltage of the detector and as you see the proportional region is one of most broad regions with proportional growth of the curve. What is that curve? "rate of charge collected" writen there on that y axis sounds kind intimidating, does it not? it could simply be replaced by "gas amplification", or simply "amplification". That common used chart is not perfect, as it would suppose there is continous discharge at geiger region (no - its not it is chocked; but what to wish from wikipedia), and streamers or SQS (self quenching streamers) are missing between proportional counters and geiger region.
A small digression:
Could our detectors work in geiger region? maybe, in case of leak from gas chamber if pressure inside the GFPC would drop below 1bar...
Could our counters get pushed into streamer mode? I would not want to find it out as that could damage counter windows. How to get closer to streamer mode: very large bias + very high photon count of high energy X-rays + reduced gas pressure (i.e. localised micro leak in the window).
The one of crucial piece to understand is that GFPC is two devices in one: detector of X-rays and adjustable amplifier.
Simplified equation of final pulse height would be something like this:
A
(PHA) = E * A
bias*A
C.S.P*shapper*A
gainwhere E is energy of X-ray photon, A
bias is amplification by townsend avalanche, A
C.S.P*shapper is fixed amplification by Charge sensitive preamplifier and shapper, and A
gain is analog amplification before pulse detection (integral mode counting) and before PHA in the signal pipeline. Only A
bias and A
gain can be adjusted. So i.e. 2 x 2 or 1 x 4 or 4 x 1 – all of these example multiplications of two different amplifications will result in the same final amplification of 4.
So if we have about 1830V bias, the E*A
bias*A
C.S.P*shapper result in this kind of amplitude for middle range of X-rays (i.e. Ti Ka, but I am not sure if it was not Ca Ka or Cr Ka) be something like this:
(https://smf.probesoftware.com/gallery/1607_17_08_22_1_40_57.bmp)
As we can read graphically the observed (by oscilloscope) amplitude of these two stages of amplification it would be about 3.1V.
Now pay attention: for Ti Ka pulse using LIF, or PET, from both of them it would produce exact same amplitude at that point in pipeline (the above oscilloscope picture) if using that same exact bias. Cameca peaksight use gain to move the pulse to different position in PHA on x axis when using "auto PHA", it would use <1 gain (number <1024 in GUI) if LIF, and >1 gain if using PET (>1024). It tries to place PHA peak to some "theoretical" position so all possible pulses for given selected XTAL in wavelenght would fit within 0-5V scale of PHA – which as we already know has actually no practical meaning. Its kind of irony that those default procedures are shitty for high count measurement: in case of PET we ironically get better set PHA exposing argon escape peak - but being exposed to much higher count rate in default Peaksight we would get massive unaccounted count rate deficit from massive "multi-photon coincidences" (compared to LIF, which would not achieve such high count rate at same beam conditions); and for LIF we would get clipped peak at low baseline, which with increasing count rate would clip it more and more. We would have in both default OEM settings poor performance on both XTALS at high current rate.
Then, this A
gain amplification is happening on WDS board in electronics box (VME card) and this amplification is in between 0 and ~4; where 1.0 (no change in amplitude) would correspond to 1024 units (max is 4096, correct? I guess 1024bits = 1, i also could be that 1000bits = 1.0 gain). Auto PHA for higher energies x-rays often set that gain below 1000, and that means [E * A
bias] part of amplification is very large, and so amplitude needs reduction before going into PHA, so it would fit inside 0-5V scale or be placed at some bizarre theoretical position.
Why it would be designed like that? I think most probable answer would be that noise in the [E * A
bias] part of signal is not amplified, where A
gain also would amplify the the noise, as it is simple direct amplification. Such assumption (of higher bias benefit) is fine if staying in low count rate (maybe <=5kcps), but it ignores dependency of amplitude multiplier A
C.S.P*shapper from [count rate]*[E * A
bias], which bites back with severe PHA type I shift which [C.S.P*shapper] combo introduce.
But if you look again to that oscilloscope snapshot above, you can see that noise floor is really low, and there is rather no problem if Gain amplification would increase it twice or even more – the peak/noise ratio would still be perfectly acceptable enough to discard the noise and pass the pulses in the pipeline. So i.e. reducing that pulses to 1.5V from 3.1V (i.e. bias down to 1700V) and then using gain to increase it to 4V (gain of 2.7 which would be ~2700 units in GUI) would produce same amplitude in that case as default Auto bias/gain of peaksight. However lower bias/higher gain would work better for higher count rates, as CSP*shapper would be less affected by lower [E * A
bias].
Another very important benefits of reduced bias.
GFPC ages - the anode gets contaminated with hydrocarbon gunk which impairs its performance.
The aging is directly proportional to number of ions of methane which breakdown into smaller components and then combines into larger hydrocarbs on the anode, which proportionally scales with gas amplification amplitude. If we use gas amplification amplitude conservatively, by reducing gas amplification we could twice or more prolong functional age of GFCP before needing a replacement (or cleaning). Bias reduction should in particularly be not neglected in case of high current used with measurement of large quantities on large crystals resulting in very high count rates.
I was just going to post a similar graphic as you did, showing the proportional response range! By the way, here's a plot of detector response as a function of barometric pressure from Jon Fellowes that I had forgotten about:
https://smf.probesoftware.com/index.php?topic=1614.msg12439#msg12439
Quote from: sem-geologist on March 20, 2026, 04:57:07 AMAnother very important benefits of reduced bias. GFPC ages - the anode gets contaminated with hydrocarbon gunk which impairs its performance.
That is good advice! Though I will say that working with Andrew recently I noticed too late that he had been trying different bias voltages and although the PHA peak (for oxygen Ka) looked OK, when we performed quant analyses the results were not good extrapolating from MgO to MgAl2O4. Basically he accidentally set the bias voltage too low and apparently the detector was not quite stable for that low an energy x-ray.
I know that on most instruments the OEM engineer usually adjusts the gain level (8, 16, 32, 64, etc. for JEOL) for each Bragg crystal for x-ray energy range (LiF, PET,. TAP, etc.). Of course on the Cameca the gain is more adjustable, but it also depends on whether one is using a 1 atm pressure detector or a 2 atm pressure detector (see screenshot of my SCALERS.DAT file below). On the JEOL I am guessing that it similarly depends on whether one is using a P-10 detector or a xenon detector. I remember from my ARL SEMQ days that as the xenon detectors age (leak) one requires more and more bias voltage to get a stable response but then they get more and more noisy, so it is suggested these sealed detectors get changed out every few years or so.
Quote from: sem-geologist on March 20, 2026, 04:57:07 AMWhy count rate starts to drop after going below ~1600V? (choose one/or both of reasons) a) as effective field around the anode in GFPC starts to be smaller than focused diffracted beam b) field is too weak to consistently produce Townsend avalanche from every X-ray produced photoelectron, and electrons are either reconnected to positive ions, or drifts without amplification to the anode where they are collected, but because no amplification they are invisible hidden in the noise of the anode.
My thinking is that one should utilize the lowest bias that provides a *stable* signal in the proportional response range of the detector, and yes, that seems to depend on the energy of the x-ray for a given Bragg crystal. Given that a stable instrument provides the most quantitative results... for our SX100, I have defined these default bias voltages for each Bragg crystal in our SCALERS.DAT configuration file:
(https://smf.probesoftware.com/gallery/395_20_03_26_8_13_48.png)
because as you mention, the lower the incoming x-ray energy, the more bias voltage that needs to be provided. Also note that spectrometers 3 and 5 are 2 atm pressure detectors and therefore require a significantly higher bias to achieve a stable proportional response.
How does one determine the proper bias voltage for a stable proportional response for a given detector for a given x-ray energy? Well, I'm sure there are many ways to decide this, but what I do is to scan a range of bias voltages and see where the x-ray signal is first produced using the Acquire and Graph Bias Scan Distribution button here:
(https://smf.probesoftware.com/gallery/395_20_03_26_8_33_23.png)
Then we see this output from the bias scan:
(https://smf.probesoftware.com/gallery/395_20_03_26_8_14_09.png)
This tells me that we want our detector bias voltage to be some tens of volts above this peak, say 1400 to 1450v for O Ka on this spectrometer. This seems to provide stable operation of the detector and it is optimized for the specific x-ray energy in question. But I am open to other methods...
Andrew and I continued with our testing of EPMA accuracy this time attempting to minimize absorption effects (which are very large in the MgAl2O4) and instead looking at elements/materials with large atomic number corrections (which are very small in MgAl2O4), for example, Fe Ka in various Fe silicates, sulfides and oxides.
Just as an example we analyzed Fe Ka on spectrometer 3 (LLIF, 2 atm P-10) and spectrometer 5 (LIF, 2 atm P-10). To start with, we aggregated the intensities of both spectrometers using the aggregate intensity feature in Probe for EPMA and we got these results for YIG (yttrium iron garnet) extrapolating from a natural magnetite (Fe3O4) as the primary standard:
Summary of All Calculated (averaged) Matrix Corrections:
St 854 Set 1 YIG single crystal (#258)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Fe Fe Y O TOTAL
1 37.815 .000 36.140 26.020 99.975 Armstrong/Brown/Scott-Love (prZ)
2 37.661 .000 36.140 26.020 99.821 Philibert/Duncumb-Reed
3 38.150 .000 36.140 26.020 100.310 Heinrich/Duncumb-Reed
4 37.753 .000 36.140 26.020 99.913 Love-Scott I
5 37.826 .000 36.140 26.020 99.986 Love-Scott II
6 37.491 .000 36.140 26.020 99.651 Packwood Phi(prZ) (EPQ-91)
7 38.519 .000 36.140 26.020 100.679 Bastin (original) (prZ)
8 37.693 .000 36.140 26.020 99.853 Bastin PROZA Phi (prZ) (EPQ-91)
9 37.694 .000 36.140 26.020 99.854 Pouchou and Pichoir-Full (PAP)
10 37.733 .000 36.140 26.020 99.893 Pouchou and Pichoir-Simplified (XPP)
11 37.795 .000 36.140 26.020 99.955 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 37.830 .000 36.140 26.020 99.990
SDEV: .278 .000 .000 .000 .278
SERR: .084 .000 .000 .000
MIN: 37.491 .000 36.140 26.020 99.651
MAX: 38.519 .000 36.140 26.020 100.679
Percent Variances:
ELEM: Fe Fe Y O
PUBL: 37.840 n.a. 36.140 26.020
STDS: 895 0 --- ---
ELEM: Fe Fe Y O
1 -.07 .00 .00 .00 Armstrong/Brown/Scott-Love (prZ)
2 -.47 .00 .00 .00 Philibert/Duncumb-Reed
3 .82 .00 .00 .00 Heinrich/Duncumb-Reed
4 -.23 .00 .00 .00 Love-Scott I
5 -.04 .00 .00 .00 Love-Scott II
6 -.92 .00 .00 .00 Packwood Phi(prZ) (EPQ-91)
7 1.80 .00 .00 .00 Bastin (original) (prZ)
8 -.39 .00 .00 .00 Bastin PROZA Phi (prZ) (EPQ-91)
9 -.39 .00 .00 .00 Pouchou and Pichoir-Full (PAP)
10 -.28 .00 .00 .00 Pouchou and Pichoir-Simplified (XPP)
11 -.12 .00 .00 .00 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -.03 .00 .00 .00
SDEV: .74 .00 .00 .00
SERR: .22 .00 .00 .00
MIN: -.92 .00 .00 .00
MAX: 1.80 .00 .00 .00
Plotting all the YIG analyses at both 15 and 20 keV we see this:
(https://smf.probesoftware.com/gallery/395_25_03_26_9_25_06.png)
Similar accuracy was seen in the other oxides and silicates, here for example a synthetic fayalite also using Fe3O4 as the primary standard at 20 keV:
Summary of All Calculated (averaged) Matrix Corrections:
St 863 Set 4 Fayalite ORNL single crystal (#263)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Fe Fe Si O TOTAL
1 54.510 .000 13.770 31.440 99.720 Armstrong/Brown/Scott-Love (prZ)
2 54.986 .000 13.770 31.440 100.196 Philibert/Duncumb-Reed
3 54.396 .000 13.770 31.440 99.606 Heinrich/Duncumb-Reed
4 54.525 .000 13.770 31.440 99.735 Love-Scott I
5 54.520 .000 13.770 31.440 99.730 Love-Scott II
6 55.050 .000 13.770 31.440 100.260 Packwood Phi(prZ) (EPQ-91)
7 54.619 .000 13.770 31.440 99.829 Bastin (original) (prZ)
8 54.789 .000 13.770 31.440 99.999 Bastin PROZA Phi (prZ) (EPQ-91)
9 54.776 .000 13.770 31.440 99.986 Pouchou and Pichoir-Full (PAP)
10 54.782 .000 13.770 31.440 99.992 Pouchou and Pichoir-Simplified (XPP)
11 54.502 .000 13.770 31.440 99.712 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 54.678 .000 13.770 31.440 99.888
SDEV: .214 .000 .000 .000 .214
SERR: .064 .000 .000 .000
MIN: 54.396 .000 13.770 31.440 99.606
MAX: 55.050 .000 13.770 31.440 100.260
Percent Variances:
ELEM: Fe Fe Si O
PUBL: 54.790 n.a. 13.770 31.440
STDS: 895 0 --- ---
ELEM: Fe Fe Si O
1 -.51 .00 .00 .00 Armstrong/Brown/Scott-Love (prZ)
2 .36 .00 .00 .00 Philibert/Duncumb-Reed
3 -.72 .00 .00 .00 Heinrich/Duncumb-Reed
4 -.48 .00 .00 .00 Love-Scott I
5 -.49 .00 .00 .00 Love-Scott II
6 .47 .00 .00 .00 Packwood Phi(prZ) (EPQ-91)
7 -.31 .00 .00 .00 Bastin (original) (prZ)
8 .00 .00 .00 .00 Bastin PROZA Phi (prZ) (EPQ-91)
9 -.03 .00 .00 .00 Pouchou and Pichoir-Full (PAP)
10 -.01 .00 .00 .00 Pouchou and Pichoir-Simplified (XPP)
11 -.53 .00 .00 .00 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -.20 .00 .00 .00
SDEV: .39 .00 .00 .00
SERR: .12 .00 .00 .00
MIN: -.72 .00 .00 .00
MAX: .47 .00 .00 .00
And here extrapolating from Fe3O4 to the NIST K-412 mineral glass:
Summary of All Calculated (averaged) Matrix Corrections:
St 807 Set 2 NBS K-412 mineral glass (#160)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Fe Fe Si Mg Ca Al Mn O TOTAL
1 7.677 .000 21.190 11.650 10.900 4.910 .070 43.597 99.994 Armstrong/Brown/Scott-Love (prZ)
2 7.863 .000 21.190 11.650 10.900 4.910 .070 43.597 100.180 Philibert/Duncumb-Reed
3 7.605 .000 21.190 11.650 10.900 4.910 .070 43.597 99.922 Heinrich/Duncumb-Reed
4 7.687 .000 21.190 11.650 10.900 4.910 .070 43.597 100.005 Love-Scott I
5 7.685 .000 21.190 11.650 10.900 4.910 .070 43.597 100.002 Love-Scott II
6 7.946 .000 21.190 11.650 10.900 4.910 .070 43.597 100.263 Packwood Phi(prZ) (EPQ-91)
7 7.723 .000 21.190 11.650 10.900 4.910 .070 43.597 100.040 Bastin (original) (prZ)
8 7.830 .000 21.190 11.650 10.900 4.910 .070 43.597 100.147 Bastin PROZA Phi (prZ) (EPQ-91)
9 7.818 .000 21.190 11.650 10.900 4.910 .070 43.597 100.136 Pouchou and Pichoir-Full (PAP)
10 7.828 .000 21.190 11.650 10.900 4.910 .070 43.597 100.145 Pouchou and Pichoir-Simplified (XPP)
11 7.668 .000 21.190 11.650 10.900 4.910 .070 43.597 99.985 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 7.757 .000 21.190 11.650 10.900 4.910 .070 43.597 100.074
SDEV: .105 .000 .000 .000 .000 .000 .000 .000 .105
SERR: .032 .000 .000 .000 .000 .000 .000 .000
MIN: 7.605 .000 21.190 11.650 10.900 4.910 .070 43.597 99.922
MAX: 7.946 .000 21.190 11.650 10.900 4.910 .070 43.597 100.263
Percent Variances:
ELEM: Fe Fe Si Mg Ca Al Mn O
PUBL: 7.740 n.a. 21.190 11.650 10.900 4.910 .070 43.597
STDS: 895 0 --- --- --- --- --- ---
ELEM: Fe Fe Si Mg Ca Al Mn O
1 -.82 .00 --- --- --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 1.59 .00 --- --- --- --- --- --- Philibert/Duncumb-Reed
3 -1.75 .00 --- --- --- --- --- --- Heinrich/Duncumb-Reed
4 -.68 .00 --- --- --- --- --- --- Love-Scott I
5 -.72 .00 --- --- --- --- --- --- Love-Scott II
6 2.67 .00 --- --- --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 -.22 .00 --- --- --- --- --- --- Bastin (original) (prZ)
8 1.16 .00 --- --- --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 1.01 .00 --- --- --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 1.14 .00 --- --- --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 -.93 .00 --- --- --- --- --- --- PAP/Donovan and Moy BSC/BKS (prZ)
AVER: .22 .00 .00 .00 .00 .00 .00 .00
SDEV: 1.36 .00 .00 .00 .00 .00 .00 .00
SERR: .41 .00 .00 .00 .00 .00 .00 .00
MIN: -1.75 .00 .00 .00 .00 .00 .00 .00
MAX: 2.67 .00 .00 .00 .00 .00 .00 .00
Still with sub percent level accuracy for DAM/PAP... and this is at 20 keV!
Regarding the earlier PHA discussion, see the below table in Hall's 1993 article in Surface Engineering on suggested PHA settings for measuring light elements on a JEOL instrument. Despite never considering it, the upper limits on the differential mode window are high enough that measurements are either very similar to, or essentially are in, integral mode.
(https://smf.probesoftware.com/gallery/3292_25_03_26_10_24_25.png)
Paper can be found here: https://doi.org/10.1179/sur.1993.9.3.205
I have a pdf if anyone wants to read the full article, but there's not a ton more PHA discussion hiding within the text.
A more general question regarding EPMA accuracy is how can EDS quant use a pure metal standard to accurately analyze oxide materials but WDS cannot?
As mentioned in this post here regarding "peak shift matching" for relatively low energy lines, I think it's because WDS has much greater spectral resolution than EDS, and therefore is more sensitive to chemical states:
https://smf.probesoftware.com/index.php?topic=127.msg14013#msg14013
As seen in the post linked above, if we adjust the WDS spectrometer position to the actual peak position on each material, we can get accurate analyses for even S ka, assuming our dead times are properly calibrated and our PHA setting are properly tuned. But even Fe Ka can exhibit subtle peak shift issues between oxidized and reduced phases. Here is analyzing NBS K-412 glass using Fe metal (#526) as a standard:
St 807 Set 3 NBS K-412 mineral glass (#160), Results in Elemental Weight Percents
ELEM: Fe Fe Si Mg Ca Al Mn O
TYPE: ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC
BGDS: LIN LIN
TIME: 60.00 .00 --- --- --- --- --- ---
BEAM: 29.87 .00 --- --- --- --- --- ---
AGGR: 2 --- --- --- --- --- ---
ELEM: Fe Fe Si Mg Ca Al Mn O SUM
XRAY: (ka) (ka) () () () () () ()
424 7.503 .000 21.190 11.650 10.900 4.910 .070 43.597 99.820
425 7.540 .000 21.190 11.650 10.900 4.910 .070 43.597 99.857
426 7.550 .000 21.190 11.650 10.900 4.910 .070 43.597 99.867
427 7.521 .000 21.190 11.650 10.900 4.910 .070 43.597 99.838
428 7.520 .000 21.190 11.650 10.900 4.910 .070 43.597 99.837
AVER: 7.527 .000 21.190 11.650 10.900 4.910 .070 43.597 99.844
SDEV: .019 .000 .000 .000 .000 .000 .000 .000 .019
SERR: .008 .000 .000 .000 .000 .000 .000 .000
%RSD: .25 .0000 .00 .00 .00 .00 .00 .00
PUBL: 7.740 n.a. 21.190 11.650 10.900 4.910 .070 43.597 100.057
%VAR: -2.76 .00 .00 .00 .00 .00 .00 .00
DIFF: -.213 --- .000 .000 .000 .000 .000 .000
STDS: 526 0 --- --- --- --- --- ---
So this error is due to the "peak shift" issues we discussed previously in the S Ka anhydrite/pyrite post.
But by re-assigning our primary standard to Fe3O4 (#895) we obtain this analysis:St 807 Set 3 NBS K-412 mineral glass (#160), Results in Elemental Weight Percents
ELEM: Fe Fe Si Mg Ca Al Mn O
TYPE: ANAL ANAL SPEC SPEC SPEC SPEC SPEC SPEC
BGDS: LIN LIN
TIME: 60.00 .00 --- --- --- --- --- ---
BEAM: 29.87 .00 --- --- --- --- --- ---
AGGR: 2 --- --- --- --- --- ---
ELEM: Fe Fe Si Mg Ca Al Mn O SUM
XRAY: (ka) (ka) () () () () () ()
424 7.673 .000 21.190 11.650 10.900 4.910 .070 43.597 99.990
425 7.712 .000 21.190 11.650 10.900 4.910 .070 43.597 100.029
426 7.722 .000 21.190 11.650 10.900 4.910 .070 43.597 100.039
427 7.692 .000 21.190 11.650 10.900 4.910 .070 43.597 100.009
428 7.691 .000 21.190 11.650 10.900 4.910 .070 43.597 100.008
AVER: 7.698 .000 21.190 11.650 10.900 4.910 .070 43.597 100.015
SDEV: .019 .000 .000 .000 .000 .000 .000 .000 .019
SERR: .008 .000 .000 .000 .000 .000 .000 .000
%RSD: .25 .0000 .00 .00 .00 .00 .00 .00
PUBL: 7.740 n.a. 21.190 11.650 10.900 4.910 .070 43.597 100.057
%VAR: -.55 .00 .00 .00 .00 .00 .00 .00
DIFF: -.042 --- .000 .000 .000 .000 .000 .000
STDS: 895 0 --- --- --- --- --- ---
That's an impressive extrapolation from the pure oxide to the NIST glass for both the dead time correction and the PHA tuning not to mention the atomic number correction!
Yes, for light elements the chemical effects are so large that we may still need to "peak shape match" or utilize Area Peak Factors.
But it seems to me that with a properly calibrated instrument we can accurately analyze any oxide/silicate materials with a pure oxide primary standard.
Yes, this is all preparation for the release of the FIGMAS synthetic mineral mount that Will Nachlas is working on!
I plotted up the quantitative results from the work Andrew and I did last weekend at 15 and 20 keV for Fe Ka on spectormeters 3 and 5 and aggregated the results using the aggregate intensities feature in PFE:
https://smf.probesoftware.com/index.php?topic=1316.0
because it's so easy! But I also calculated the data for each spectrometer separately but they all agree quite well, so why not improve precision if one can?
Here are results for Fe Ka using Fe metal as a primary standard measuring a pure natural pyrite as a secondary standard:
(https://smf.probesoftware.com/gallery/395_27_03_26_10_08_16.png)
The relative accuracy errors are less that 0.5% and all within the variance. Next I plotted up synthetic YIG (yttrium iron garnet) using Fe3O4 as a primary standard (because of the subtle chemical shift between oxidized and reduced iron which the LiF WDS crystal can resolve):
(https://smf.probesoftware.com/gallery/395_27_03_26_10_08_35.png)
and again excellent accuracy at both 15 and 20 keV. Now to test the dead time extrapolation and the atomic number correction we measured the NBS K-412 mineral glass again with Fe3O4 as the primary standard:
(https://smf.probesoftware.com/gallery/395_27_03_26_10_08_51.png)
Excellent accuracy at 15 keV and about a 1% relative error at 20 keV (approximately a difference of ~800 PPM from the published value, so not too bad!
Now, here's the shocking part. Let's look at the PHA scans for these two spectrometers, first we'll start with spectrometer 5 LiF (2 atm P-10):
(https://smf.probesoftware.com/gallery/395_27_03_26_10_12_16.png)
Looks pretty normal, right? Now let's see the LLIF diffractor PHA scan on spectrometer 3 (which would dominate these aggregated intensities because it's a *large* LIF):
(https://smf.probesoftware.com/gallery/395_27_03_26_10_12_35.png)
Don't be surprised. Remember, all photons to the right will be counted in integral PHA mode! The key is that your PHA peak needs to be *completely* above the PHA baseline when measuring the highest intensity you expect to measure, usually ones primary standard, in this case Fe metal, to ensure a linear response from your counting electronics.
"If one is aiming for +/-30% accuracy, well nothing really matters, though if one is looking for +/-10% accuracy, well then a few things matter, but if one is trying to obtain +/-1% accuracy, then everything matters! 🙂
Over the last few months Andrew and I have been doing some measurements on our Cameca instrument, and we're finally starting to put two and two together:
https://smf.probesoftware.com/index.php?topic=1831.0
In other words, here's the gist of why some people still think they need to "matrix match" their standard and their unknown:
1. Due to the high spectral resolution of WDS (unlike EDS!) we must at least utilize a rough "peak shift" match. That is, we must use an oxide (oxidized) standard for oxides/silicates and an elemental (reduced) standard for alloys/sulfides:
https://smf.probesoftware.com/index.php?topic=1423.msg11809#msg11809
Though interestingly we don't need to "peak shift match" if we adjust our WDS peak position for each phase:
https://smf.probesoftware.com/index.php?topic=127.msg14013#msg14013
Yes, for very light elements (e.g., O, N, C, etc.) the chemical effects are so large for WDS that we may still need to "peak shape match" or utilize Area Peak Factors.
2. But when adjusting our PHA settings, we *do not* need to "count rate match" our standard and unknown. That is, if we adjust the PHA bias/gain properly (there's the rub!) and utilize integral mode using just the baseline level. Properly tuning our PHA allows the use of high purity synthetic metal or oxide materials as primary standards when the count rates are very different compared to our unknowns, even with severe pulse height depression.
But what if there are high order spectral interferences? That's OK. Let them in and correct for them quantitatively using software! But don't use the PHA window differential to induce a non-linear response in our counting electronics!
https://smf.probesoftware.com/index.php?topic=1466.msg13955#msg13955
https://smf.probesoftware.com/index.php?topic=1831.msg14015#msg14015
3. Our quantitative accuracy will improve significantly when we no longer rely on heterogeneous natural "matrix matched" standards. Because our counting electronics response will be totally linear with this method of PHA tuning. By following these steps we can achieve high accuracy quantitative EPMA:
https://smf.probesoftware.com/index.php?topic=1831.msg14011#msg14011
https://smf.probesoftware.com/index.php?topic=1823.msg13926#msg13926
4. And of course if we no longer need to "count rate match" our standard and unknown, we need to have carefully calibrated our dead time constants using the constant k-ratio method, and possibly utilize the non-linear dead time expression:
https://smf.probesoftware.com/index.php?topic=1466.msg13255#msg13255
As I said at the beginning of this post: 2 + 2 = 4! :D
Thus, we can achieve sub 1% quantitative accuracy in EPMA if we utilize high purity, end member synthetic standards with a minimal "peak shift match" for oxidized vs. reduced chemical states, follow the PHA tuning steps described above, along with well calibrated dead time constants. Let's test this hypothesis on more instruments!
If anyone would like to see the data from our Fe Ka testing that Andrew and I did last weekend I've attached it below. See this post for some examples and conclusions:
https://smf.probesoftware.com/index.php?topic=1831.msg14015#msg14015
One comment: the chromite "standard" (#896) is a natural material I sourced from the Berkeley mineral collection back in the 1980s and should not be considered to have an accurate composition in any sense. Same goes for the pyrrhotite "standard" (#757), it's just a natural mineral with an assumed composition originally used for peak shift tests.
I found some Pb and As analyses I did back in 2015 and it appears I never posted them probably because using the Armstrong pr(z) matrix corrections they didn't come out very well (as we all know, the Pb La and As Ka overlap is the worst!).
Here is the analysis of PbS using FeS2 as the primary sulfur standard using Pb La and the Armstrong pr(z) (and Henke MACs):
St 731 Set 2 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM: S Pb As
TYPE: ANAL ANAL ANAL
BGDS: LIN EXP EXP
TIME: 80.00 80.00 80.00
BEAM: 29.88 29.88 29.88
ELEM: S Pb As SUM
333 14.997 87.319 -.148 102.167
334 14.976 87.067 -.055 101.988
335 15.051 86.071 .521 101.643
AVER: 15.008 86.819 .106 101.933
SDEV: .039 .660 .363 .266
SERR: .022 .381 .209
%RSD: .26 .76 342.11
PUBL: 13.400 86.600 n.a. 100.000
%VAR: 12.00 (.25) ---
DIFF: 1.608 (.22) ---
STDS: 730 731 662
Note that the sulfur analysis here is off by ~12% relative, so not very good. Let's switch to the FFAST MACs:
St 731 Set 2 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM: S Pb As
TYPE: ANAL ANAL ANAL
BGDS: LIN EXP EXP
TIME: 80.00 80.00 80.00
BEAM: 29.88 29.88 29.88
ELEM: S Pb As SUM
333 14.357 87.101 -.143 101.315
334 14.336 86.837 -.050 101.123
335 14.413 85.806 .537 100.756
AVER: 14.368 86.581 .115 101.065
SDEV: .040 .684 .369 .284
SERR: .023 .395 .213
%RSD: .28 .79 320.88
PUBL: 13.400 86.600 n.a. 100.000
%VAR: 7.23 (-.02) ---
DIFF: .968 (-.02) ---
STDS: 730 731 662
Well that's a little better as the error is now only ~7% relative. OK now let's try again using the Donovan and Moy DAM/PAP matrix correction using Z fractions for the backscatter correction:
St 731 Set 2 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM: S Pb As
TYPE: ANAL ANAL ANAL
BGDS: LIN EXP EXP
TIME: 80.00 80.00 80.00
BEAM: 29.88 29.88 29.88
ELEM: S Pb As SUM
333 13.218 86.664 -.132 99.750
334 13.200 86.404 -.040 99.563
335 13.285 85.339 .555 99.179
AVER: 13.234 86.136 .128 99.498
SDEV: .045 .702 .373 .291
SERR: .026 .405 .215
%RSD: .34 .82 292.39
PUBL: 13.400 86.600 n.a. 100.000
%VAR: -1.24 (-.54) ---
DIFF: -.166 (-.46) ---
STDS: 730 731 662
OK, I can live with an ~1.2% relative error!
But just for fun, lets try the DAM "zero" exponent which calculates the exponent based on Andrew Ducharme and Aurelien Moy's work:
https://smf.probesoftware.com/index.php?topic=1566.msg12051#msg12051
https://academic.oup.com/mam/article/30/Supplement_1/ozae044.088/7719396
St 731 Set 2 Galena U.C. #7400, Results in Elemental Weight Percents
ELEM: S Pb As
TYPE: ANAL ANAL ANAL
BGDS: LIN EXP EXP
TIME: 80.00 80.00 80.00
BEAM: 29.88 29.88 29.88
ELEM: S Pb As SUM
333 13.248 86.676 -.132 99.791
334 13.230 86.415 -.040 99.605
335 13.316 85.351 .556 99.223
AVER: 13.264 86.147 .128 99.539
SDEV: .045 .702 .374 .290
SERR: .026 .405 .216
%RSD: .34 .81 292.74
PUBL: 13.400 86.600 n.a. 100.000
%VAR: -1.01 (-.52) ---
DIFF: -.136 (-.45) ---
STDS: 730 731 662
OK, now we have only 1% relative error extrapolating from FeS2 to PbS. That's a difference in average atomic number between of FeS2 and PbS standard of ~20 to 67 with an ~30% atomic number correction!
ELEMENT ABSCOR FLUCOR ZEDCOR ZAFCOR STP-POW BKS-COR F(x)u Ec Eo/Ec MACs STDNUM uZAF/sZAF
S ka 1.3328 1.0000 .7185 .9576 .5736 1.2526 .6745 2.4720 8.0906 783.125 730 .85342
Pb la .9944 .9999 1.0869 1.0807 1.1167 .9733 .9677 13.0340 1.5344 95.6487 731 1.0016
As ka 1.0249 1.0000 .8357 .8565 .7829 1.0675 .9651 11.8670 1.6853 95.8321 662 .82411
Try it for yourself...
Quote from: Probeman on March 13, 2026, 04:02:19 PM...And yes, there are a few "black holes" in the periodic table that may require a roughly similar matrix, e.g., Si Ka in Hf due to disagreement in mass absorption coefficients. But geological silicates and oxides are pretty well handled by modern matrix corrections."
While Andrew Ducharme and I are waiting for some time on the instrument, I decided to take a look back at some old runs I did on our old SX50 (which has long been scrapped), and see if I examined any of the synthetic silicates standards we had obtained from various sources when I was at UC Berkeley. I found the following run from 2014 when I was still using differential PHA tuning, which we now know produces less accurate results as described here:
https://smf.probesoftware.com/index.php?topic=1831.msg13978#msg13978
So while we wait to re-run these materials using SiO2 as the primary standard on our Sx100, here are the results from the Evaluate program for Si Ka in these materials:
https://smf.probesoftware.com/index.php?topic=340.0
2 St 12 Set 1 MgO synthetic
3 St 14 Set 1 SiO2 synthetic
4 St 16 Set 1 ThSiO4 (Thorite)
5 St 19 Set 1 HfSiO4 (Hafnon)
6 St 25 Set 1 MnO synthetic
7 St 257 Set 1 Zircon crystal (synthetic)
8 St 263 Set 1 Fe2SiO4 (synthetic fayalite)
9 St 272 Set 1 Ni2SiO4 (synthetic)
10 St 273 Set 1 Mg2SiO4 (magnesium olivine) synthetic
11 St 274 Set 1 Co2SiO4 (cobalt olivine) synthetic
12 St 275 Set 1 Mn2SiO4 (manganese olivine) synthetic
13 St 358 Set 1 Diopside (Chesterman)
14 St 386 Set 1 Alamosite (PbSiO3)
(https://smf.probesoftware.com/gallery/395_10_04_26_2_28_37.png)
The big outlier is Si Ka in HfSiO4 (hafnon) synthesized by John Hanchar. Note the 45% relative accuracy in the quant:
St 19 Set 2 HfSiO4 (Hafnon), Results in Elemental Weight Percents
SPEC: Th Hf Pb Co Ni Zr Al Ca Ti O
TYPE: SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC
AVER: .000 65.967 .000 .000 .000 .000 .000 .000 .000 23.653
SDEV: .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
ELEM: Si Mg Mn Fe
BGDS: MAN MAN MAN MAN
TIME: 60.00 60.00 60.00 60.00
BEAM: 30.13 30.13 30.13 30.13
ELEM: Si Mg Mn Fe SUM
86 15.092 .026 .043 .032 104.813
87 15.126 .024 .030 .035 104.835
88 15.122 .029 .038 .039 104.848
89 15.094 .027 .039 .031 104.811
90 15.078 .025 .047 .030 104.799
AVER: 15.102 .026 .040 .034 104.821
SDEV: .021 .002 .006 .004 .020
SERR: .009 .001 .003 .002
%RSD: .14 6.98 15.97 10.86
PUBL: 10.380 n.a. n.a. n.a. 100.000
%VAR: 45.49 --- --- ---
DIFF: 4.722 --- --- ---
STDS: 14 12 25 395
STKF: .3884 .4222 .7420 .6869
STCT: 1002.33 906.18 379.64 336.38
UNKF: .0565 .0002 .0004 .0004
UNCT: 145.83 .35 .21 .18
UNBG: 2.03 1.43 .89 1.10
ZCOR: 2.6725 1.6261 .9765 .9241
KRAW: .1455 .0004 .0005 .0005
PKBG: 72.96 1.24 1.23 1.16
This is because of the large absorption correction due to the Si Ka line being near the Hf M edge. The MAC from FFAST is only very slightly better. Remember in cases of large absorption corrections our matrix corrections are only as good as our mass absorption coefficients!
What I did at the time was to empirically measure the MAC for Si Ka in Hf using the method of Pouchou:
https://smf.probesoftware.com/index.php?topic=1340.msg9631#msg9631
After utilizing this experimental MAC from the EMPMAC.DAT file:
we now obtain these results:
(https://smf.probesoftware.com/gallery/395_10_04_26_2_28_52.png)
Here for comparison is the HfSiO4 again:
St 19 Set 2 HfSiO4 (Hafnon), Results in Elemental Weight Percents
SPEC: Th Hf Pb Co Ni Zr Al Ca Ti O
TYPE: SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC SPEC
AVER: .000 65.967 .000 .000 .000 .000 .000 .000 .000 23.653
SDEV: .000 .000 .000 .000 .000 .000 .000 .000 .000 .000
ELEM: Si Mg Mn Fe
BGDS: MAN MAN MAN MAN
TIME: 60.00 60.00 60.00 60.00
BEAM: 30.13 30.13 30.13 30.13
ELEM: Si Mg Mn Fe SUM
86 10.924 .027 .039 .027 100.636
87 10.950 .024 .025 .030 100.649
88 10.947 .029 .034 .034 100.664
89 10.925 .027 .035 .026 100.633
90 10.914 .025 .042 .025 100.625
AVER: 10.932 .026 .035 .028 100.641
SDEV: .016 .002 .006 .004 .015
SERR: .007 .001 .003 .002
%RSD: .14 7.01 17.95 12.71
PUBL: 10.380 n.a. n.a. n.a. 100.000
%VAR: 5.32 --- --- ---
DIFF: .552 --- --- ---
STDS: 14 12 25 395
STKF: .3884 .4222 .7420 .6869
STCT: 1002.33 906.18 379.64 336.38
UNKF: .0562 .0002 .0004 .0003
UNCT: 145.00 .34 .18 .15
UNBG: 2.85 1.43 .91 1.13
ZCOR: 1.9456 1.6431 .9672 .9145
KRAW: .1447 .0004 .0005 .0005
PKBG: 51.81 1.24 1.20 1.13
5% accuracy is a lot better than 45%!
The other silicates are all around ~1 to 2% accuracy. Can't wait to re-run these materials using integral PHA mode on a more modern instrument.
Quote from: Probeman on March 27, 2026, 10:31:42 AMNow, here's the shocking part. Let's look at the PHA scans for these two spectrometers, first we'll start with spectrometer 5 LiF (2 atm P-10):
(https://smf.probesoftware.com/gallery/395_27_03_26_10_12_16.png)
Looks pretty normal, right? Now let's see the LLIF diffractor PHA scan on spectrometer 3 (which would dominate these aggregated intensities because it's a *large* LIF):
(https://smf.probesoftware.com/gallery/395_27_03_26_10_12_35.png)
Don't be surprised. Remember, all photons to the right will be counted in integral PHA mode! The key is that your PHA peak needs to be *completely* above the PHA baseline when measuring the highest intensity you expect to measure, usually ones primary standard, in this case Fe metal, to ensure a linear response from your counting electronics.
Andrew and I re-plotted all the oxide/silicate/sulfide data for Fe Ka at both 15 and 20 keV from our run the other weekend for a few materials, to visualize accuracy extrapolating from our magnetite (Fe3O4) which has wet chemistry performed by Ian Carmichael back in the 1990s, or our Fe metal standards, to test when there are large changes in the count rate and the atomic number corrections (and small absorption corrections).
These plots show data for spec 3 (LLIF), spec5 (LIF) and spec 3 and 5 aggregated intensities. The point being that although the PHA scans look quite different, spec 3 yields similar or better accuracy to spec 5!
Here are the analyses for pyrite using Fe metal as a primary standard:
(https://smf.probesoftware.com/gallery/395_13_04_26_1_20_09.png)
Now for YIG using Fe3O4 as the primary standard:
(https://smf.probesoftware.com/gallery/395_13_04_26_1_20_51.png)
And SRM K-412 glass again using Fe3O4 as the primary standard:
(https://smf.probesoftware.com/gallery/395_13_04_26_1_21_23.png)
The NIST glass shows the worst accuracy, but still around 1% or better accuracy extrapolating from Fe3O4. Just to compare, here is the output for NIST K-411 which has a slightly higher Fe content:
Summary of All Calculated (averaged) Matrix Corrections:
St 162 Set 1 NBS K-411 mineral glass
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Fe Fe Si Mg Ca Al Mn O TOTAL
1 11.232 .000 25.382 8.847 11.057 .053 .077 43.558 100.207 Armstrong/Brown/Scott-Love (prZ)
2 11.438 .000 25.382 8.847 11.057 .053 .077 43.558 100.413 Philibert/Duncumb-Reed
3 11.104 .000 25.382 8.847 11.057 .053 .077 43.558 100.078 Heinrich/Duncumb-Reed
4 11.235 .000 25.382 8.847 11.057 .053 .077 43.558 100.209 Love-Scott I
5 11.237 .000 25.382 8.847 11.057 .053 .077 43.558 100.211 Love-Scott II
6 11.393 .000 25.382 8.847 11.057 .053 .077 43.558 100.367 Packwood Phi(prZ) (EPQ-91)
7 11.109 .000 25.382 8.847 11.057 .053 .077 43.558 100.083 Bastin (original) (prZ)
8 11.399 .000 25.382 8.847 11.057 .053 .077 43.558 100.373 Bastin PROZA Phi (prZ) (EPQ-91)
9 11.389 .000 25.382 8.847 11.057 .053 .077 43.558 100.364 Pouchou and Pichoir-Full (PAP)
10 11.398 .000 25.382 8.847 11.057 .053 .077 43.558 100.372 Pouchou and Pichoir-Simplified (XPP)
11 11.194 .000 25.382 8.847 11.057 .053 .077 43.558 100.168 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 11.285 .000 25.382 8.847 11.057 .053 .077 43.558 100.259
SDEV: .123 .000 .000 .000 .000 .000 .000 .000 .123
SERR: .037 .000 .000 .000 .000 .000 .000 .000
MIN: 11.104 .000 25.382 8.847 11.057 .053 .077 43.558 100.078
MAX: 11.438 .000 25.382 8.847 11.057 .053 .077 43.558 100.413
Percent Variances:
ELEM: Fe Fe Si Mg Ca Al Mn O
PUBL: 11.209 n.a. 25.382 8.847 11.057 .053 .077 43.558
STDS: 895 0 --- --- --- --- --- ---
ELEM: Fe Fe Si Mg Ca Al Mn O
1 .21 .00 --- --- --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 2.05 .00 --- --- --- --- --- --- Philibert/Duncumb-Reed
3 -.94 .00 --- --- --- --- --- --- Heinrich/Duncumb-Reed
4 .24 .00 --- --- --- --- --- --- Love-Scott I
5 .25 .00 --- --- --- --- --- --- Love-Scott II
6 1.64 .00 --- --- --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 -.89 .00 --- --- --- --- --- --- Bastin (original) (prZ)
8 1.69 .00 --- --- --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 1.61 .00 --- --- --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 1.69 .00 --- --- --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 -.13 .00 --- --- --- --- --- --- PAP/Donovan and Moy BSC/BKS (prZ)
AVER: .67 .00 .00 .00 .00 .00 .00 .00
SDEV: 1.10 .00 .00 .00 .00 .00 .00 .00
SERR: .33 .00 .00 .00 .00 .00 .00 .00
MIN: -.94 .00 .00 .00 .00 .00 .00 .00
MAX: 2.05 .00 .00 .00 .00 .00 .00 .00
The moral of this story is that we no longer need to matrix match our primary standards to our unknown if we have:
1. Calibrated our dead times accurately using the constant k-ratio method:
https://smf.probesoftware.com/index.php?topic=1466.msg11102#msg11102
2. Checked our WD spectrometer alignments using the Bragg order k-ratio method:
https://smf.probesoftware.com/index.php?topic=1739.0
3. Properly tuned our PHA electronics using integral mode with enough gain (or bias) to keep our PHA *completely* above the baseline level at the highest count rate (generally the highest concentration at highest beam current) we expect to observe:
https://smf.probesoftware.com/index.php?topic=1475.msg11330#msg11330
4. Utilize a modern matrix correction with a Z based backscatter correction for large changes in average atomic number:
https://smf.probesoftware.com/index.php?topic=1566.0
5. Utilize high purity synthetic end member minerals/materials which can be distributed globally and replenished "ad infinitum":
https://smf.probesoftware.com/index.php?topic=1415.msg10368;topicseen#msg10368
Every lab should be taking these steps immediately for best accuracy EPMA... what are you waiting for?
Quote from: Probeman on April 10, 2026, 02:42:38 PMWhile Andrew Ducharme and I are waiting for some time on the instrument, I decided to take a look back at some old runs I did on our old SX50 (which has long been scrapped), and see if I examined any of the synthetic silicates standards we had obtained from various sources when I was at UC Berkeley. I found the following run from 2014 when I was still using differential PHA tuning, which we now know produces less accurate results as described here:
We got a run going yesterday for these same synthetic silicates that I ran back in 2014, but this time I also acquired some end member primary standards, specifically SiO2 for Si Ka, Fe3O4 for Fe Ka, MgO for Mg Ka and MnO for Mn Ka.
By the way, with these synthetic silicates I am just assuming formula stoichiometry for the compositions. The only natural materials are the Fe3O4 and that was analyzed for FeO and Fe2O3 using wet chemistry by Ian Carmichael and traces using the probe and the alamosite (PbSiO3) which is a crystal clear material and assumed stoichiometric.
Here are a few analyses using the new baseline integral PHA tuning method discussed in previous posts in this topic, first Fe2SiO4 at 15 keV:
Summary of All Calculated (averaged) Matrix Corrections:
St 263 Set 1 Fe2SiO4 (synthetic fayalite)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Mn Fe O TOTAL
1 13.943 -.002 -.007 55.362 31.407 100.703 Armstrong/Brown/Scott-Love (prZ)
2 13.445 -.002 -.007 55.755 31.407 100.599 Philibert/Duncumb-Reed
3 13.994 -.002 -.007 55.210 31.407 100.602 Heinrich/Duncumb-Reed
4 13.723 -.002 -.007 55.358 31.407 100.480 Love-Scott I
5 13.857 -.002 -.007 55.364 31.407 100.619 Love-Scott II
6 12.947 -.002 -.007 55.582 31.407 99.927 Packwood Phi(prZ) (EPQ-91)
7 13.649 -.002 -.007 55.221 31.407 100.268 Bastin (original) (prZ)
8 13.709 -.002 -.007 55.569 31.407 100.676 Bastin PROZA Phi (prZ) (EPQ-91)
9 13.588 -.002 -.007 55.556 31.407 100.542 Pouchou and Pichoir-Full (PAP)
10 13.590 -.002 -.007 55.561 31.407 100.550 Pouchou and Pichoir-Simplified (XPP)
11 13.894 -.002 -.007 55.320 31.407 100.612 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 13.667 -.002 -.007 55.442 31.407 100.507
SDEV: .292 .000 .000 .173 .000 .225
SERR: .088 .000 .000 .052 .000
MIN: 12.947 -.002 -.007 55.210 31.407 99.927
MAX: 13.994 -.002 -.007 55.755 31.407 100.703
Percent Variances:
ELEM: Si Mg Mn Fe O
PUBL: 13.785 n.a. n.a. 54.809 31.407
STDS: 14 12 25 395 ---
ELEM: Si Mg Mn Fe O
1 1.14 --- --- 1.01 --- Armstrong/Brown/Scott-Love (prZ)
2 -2.46 --- --- 1.73 --- Philibert/Duncumb-Reed
3 1.51 --- --- .73 --- Heinrich/Duncumb-Reed
4 -.45 --- --- 1.00 --- Love-Scott I
5 .52 --- --- 1.01 --- Love-Scott II
6 -6.08 --- --- 1.41 --- Packwood Phi(prZ) (EPQ-91)
7 -.99 --- --- .75 --- Bastin (original) (prZ)
8 -.55 --- --- 1.39 --- Bastin PROZA Phi (prZ) (EPQ-91)
9 -1.43 --- --- 1.36 --- Pouchou and Pichoir-Full (PAP)
10 -1.41 --- --- 1.37 --- Pouchou and Pichoir-Simplified (XPP)
11 .79 --- --- .93 --- PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -.85 .00 .00 1.15 .00
SDEV: 2.12 .00 .00 .31 .00
SERR: .64 .00 .00 .09 .00
MIN: -6.08 .00 .00 .73 .00
MAX: 1.51 .00 .00 1.73 .00
Si and Fe are within 1% relative accuracy, so that is pretty good for extrapolating from SiO2 and Fe3O4! Now let's try Fe2SiO4 at 20 keV:
Summary of All Calculated (averaged) Matrix Corrections:
St 263 Set 2 Fe2SiO4 (synthetic fayalite)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Mn Fe O TOTAL
1 13.769 -.008 -.005 54.802 31.407 99.965 Armstrong/Brown/Scott-Love (prZ)
2 13.189 -.007 -.005 55.238 31.407 99.821 Philibert/Duncumb-Reed
3 13.561 -.008 -.005 54.683 31.407 99.638 Heinrich/Duncumb-Reed
4 13.557 -.008 -.005 54.809 31.407 99.760 Love-Scott I
5 13.705 -.008 -.005 54.810 31.407 99.909 Love-Scott II
6 12.602 -.007 -.006 55.276 31.407 99.271 Packwood Phi(prZ) (EPQ-91)
7 13.444 -.008 -.005 54.895 31.407 99.733 Bastin (original) (prZ)
8 13.507 -.008 -.005 55.064 31.407 99.965 Bastin PROZA Phi (prZ) (EPQ-91)
9 13.357 -.008 -.005 55.045 31.407 99.797 Pouchou and Pichoir-Full (PAP)
10 13.331 -.008 -.005 55.051 31.407 99.775 Pouchou and Pichoir-Simplified (XPP)
11 13.735 -.008 -.005 54.793 31.407 99.922 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 13.433 -.008 -.005 54.951 31.407 99.778
SDEV: .329 .000 .000 .195 .000 .197
SERR: .099 .000 .000 .059 .000
MIN: 12.602 -.008 -.006 54.683 31.407 99.271
MAX: 13.769 -.007 -.005 55.276 31.407 99.965
Percent Variances:
ELEM: Si Mg Mn Fe O
PUBL: 13.785 n.a. n.a. 54.809 31.407
STDS: 14 12 25 395 ---
ELEM: Si Mg Mn Fe O
1 -.12 --- --- -.01 --- Armstrong/Brown/Scott-Love (prZ)
2 -4.32 --- --- .78 --- Philibert/Duncumb-Reed
3 -1.62 --- --- -.23 --- Heinrich/Duncumb-Reed
4 -1.65 --- --- .00 --- Love-Scott I
5 -.58 --- --- .00 --- Love-Scott II
6 -8.58 --- --- .85 --- Packwood Phi(prZ) (EPQ-91)
7 -2.47 --- --- .16 --- Bastin (original) (prZ)
8 -2.02 --- --- .47 --- Bastin PROZA Phi (prZ) (EPQ-91)
9 -3.10 --- --- .43 --- Pouchou and Pichoir-Full (PAP)
10 -3.30 --- --- .44 --- Pouchou and Pichoir-Simplified (XPP)
11 -.36 --- --- -.03 --- PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -2.56 .00 .00 .26 .00
SDEV: 2.39 .00 .00 .36 .00
SERR: .72 .00 .00 .11 .00
MIN: -8.58 .00 .00 -.23 .00
MAX: -.12 .00 .00 .85 .00
OK, now that sort accuracy is just silly! :D
Let's get really crazy now and analyze the PbSiO3 for Si, which is an enormous atomic number extrapolation from SiO2:
Summary of All Calculated (averaged) Matrix Corrections:
St 386 Set 1 Alamosite (PbSiO3)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Mn Fe Pb O TOTAL
1 10.288 -.009 -.004 -.001 73.151 16.939 100.365 Armstrong/Brown/Scott-Love (prZ)
2 8.856 -.008 -.004 -.001 73.151 16.939 98.934 Philibert/Duncumb-Reed
3 9.961 -.008 -.004 -.001 73.151 16.939 100.038 Heinrich/Duncumb-Reed
4 9.595 -.008 -.004 -.001 73.151 16.939 99.673 Love-Scott I
5 9.665 -.008 -.004 -.001 73.151 16.939 99.742 Love-Scott II
6 8.170 -.007 -.004 -.001 73.151 16.939 98.249 Packwood Phi(prZ) (EPQ-91)
7 10.315 -.009 -.004 -.001 73.151 16.939 100.391 Bastin (original) (prZ)
8 9.591 -.008 -.004 -.001 73.151 16.939 99.668 Bastin PROZA Phi (prZ) (EPQ-91)
9 9.493 -.008 -.004 -.001 73.151 16.939 99.570 Pouchou and Pichoir-Full (PAP)
10 9.375 -.008 -.004 -.001 73.151 16.939 99.453 Pouchou and Pichoir-Simplified (XPP)
11 9.808 -.009 -.004 -.001 73.151 16.939 99.885 PAP/Donovan and Moy BSC/BKS (prZ)
AVER: 9.556 -.008 -.004 -.001 73.151 16.939 99.633
SDEV: .617 .001 .000 .000 .000 .000 .616
SERR: .186 .000 .000 .000 .000 .000
MIN: 8.170 -.009 -.004 -.001 73.151 16.939 98.249
MAX: 10.315 -.007 -.004 -.001 73.151 16.939 100.391
Percent Variances:
ELEM: Si Mg Mn Fe Pb O
PUBL: 9.910 n.a. n.a. n.a. 73.151 16.939
STDS: 14 12 25 395 --- ---
ELEM: Si Mg Mn Fe Pb O
1 3.82 --- --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 -10.64 --- --- --- --- --- Philibert/Duncumb-Reed
3 .51 --- --- --- --- --- Heinrich/Duncumb-Reed
4 -3.18 --- --- --- --- --- Love-Scott I
5 -2.47 --- --- --- --- --- Love-Scott II
6 -17.56 --- --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 4.09 --- --- --- --- --- Bastin (original) (prZ)
8 -3.22 --- --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 -4.21 --- --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 -5.40 --- --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 -1.03 --- --- --- --- --- PAP/Donovan and Moy BSC/BKS (prZ)
AVER: -3.57 .00 .00 .00 .00 .00
SDEV: 6.22 .00 .00 .00 .00 .00
SERR: 1.88 .00 .00 .00 .00 .00
MIN: -17.56 .00 .00 .00 .00 .00
MAX: 4.09 .00 .00 .00 .00 .00
OK, a bit over 1% relative accuracy but still, take a look at the other matrix corrections... though it is a bit interesting that the ancient Heinrich method does so well in this one particular instance!
We re-ran the synthetic silicate standards again at both 15 and 20 keV (30 nA). Here are the full set of analyses for the two days (no disabled points), using Armstrong/DAM matrix corrections with FFAST MACs:
(https://smf.probesoftware.com/gallery/395_20_04_26_10_56_05.png)
There was one single point just above 1% error (and the average of that sample was well within 1% accuracy), but all the other points were well within 1% relative accuracy.
Now just to "knock your socks off" here was the PHA tuning we used for Fe Ka:
(https://smf.probesoftware.com/gallery/395_20_04_26_11_04_44.png)
Do you want to "break" the EPMA 1% accuracy barrier? You need to make sure your PHA peaks are completely above the baseline level at the highest count rate you anticipate measuring and be in *integral* PHA mode. And you should follow the steps outlined here and above posts:
1. Calibrate our dead times accurately using the constant k-ratio method:
https://smf.probesoftware.com/index.php?topic=1466.msg11102#msg11102
2. Check our WD spectrometer alignments using the Bragg order k-ratio method:
https://smf.probesoftware.com/index.php?topic=1739.0
3. Properly tune our PHA electronics using integral mode with enough gain (or bias) to keep our PHA *completely* above the baseline level at the highest count rate (generally the highest concentration at highest beam current) we expect to observe:
https://smf.probesoftware.com/index.php?topic=1475.msg11330#msg11330
4. Utilize a modern matrix correction with a Z based backscatter correction for large changes in average atomic number, specifically the Armstrong/DAM (Donovan and Moy) backscatter correction in Probe for EPMA:
https://smf.probesoftware.com/index.php?topic=1566.0
5. Utilize high purity synthetic end member minerals/materials which can be distributed globally and replenished "ad infinitum":
https://smf.probesoftware.com/index.php?topic=1415.msg10368;topicseen#msg10368
It's so easy! What are you waiting for? Please show us what your instrument can do with regards to high accuracy EPMA...
Looking at Mg2SiO4 synthetic (similar material to what Will Nachlas is obtaining for the MAS standard effort), we see this for Mg Ka in Mg2SiO4 using MgO as the primary standard at both 15 and 20 keV:
(https://smf.probesoftware.com/gallery/395_21_04_26_12_06_22.png)
Pretty much all within 1% relative accuracy. Now looking at Si Ka in Mg2SiO4 using SiO2 as the primary standard:
(https://smf.probesoftware.com/gallery/395_21_04_26_12_07_05.png)
The 15 keV Si Ka data are all within 1% relative error but the 20 keV data are only within about 2% relative error. Though it is interesting that the data are centered around the published value...
Continuing with our "Breaking the EPMA 1% accuracy barrier" of the day post we have first, Si Ka in Fe2SiO4 (synthetic) using SiO2 (synthetic) as a primary standard at both 15 and 20 keV:
(https://smf.probesoftware.com/gallery/395_22_04_26_9_41_13.png)
and just for fun, Si Ka in Mn2SiO4 (synthetic) again, using SiO2 as the primary standard, at 15 and 20 keV:
(https://smf.probesoftware.com/gallery/395_22_04_26_9_38_10.png)
Quote from: Probeman on April 20, 2026, 11:09:55 AMNow just to "knock your socks off" here was the PHA tuning we used for Fe Ka:
(https://smf.probesoftware.com/gallery/395_20_04_26_11_04_44.png)
Do you want to "break" the EPMA 1% accuracy barrier? You need to make sure your PHA peaks are completely above the baseline level at the highest count rate you anticipate measuring and be in *integral* PHA mode.
Paul Carpenter, 2008: "Avoid tight PHA window, use integral mode unless a PHA interference is observed" and "Use integral mode unless PHA energy discrimination required" (https://epmalab.uoregon.edu/Workshop2/Carpenter_Oregon_Workshop_2007.pdf)
Quote from: aducharme on April 27, 2026, 12:08:51 AMQuote from: Probeman on April 20, 2026, 11:09:55 AMDo you want to "break" the EPMA 1% accuracy barrier? You need to make sure your PHA peaks are completely above the baseline level at the highest count rate you anticipate measuring and be in *integral* PHA mode.
Paul Carpenter, 2008: "Avoid tight PHA window, use integral mode unless a PHA interference is observed" and "Use integral mode unless PHA energy discrimination required" (https://epmalab.uoregon.edu/Workshop2/Carpenter_Oregon_Workshop_2007.pdf)
Nice find.
Yes, Paul has been saying this all along, but there's a critical component that I'm not seeing in his presentation.
For example, he says: "Low energy pulses must be discriminated from baseline noise. Need proper setting of noise threshold, baseline, and window settings of WDS pulse height analyzer."
And that is certainly true. But it would be better to merely say: make sure that the PHA peak is completely above the baseline level at the highest count rate that one intends to measure.
Then there is no need to perform "count rate matching" as he claims a bit later on: "Pulse energy shift with varying count rate results in instability. At high count rates pulses are poorly discriminated from baseline noise.
Use similar count rates on standard and sample". I say we don't need to "count rate match" if we tune our PHAs properly...
Also, it's not "instability" that occurs with "pulse energy shift" or what I would call "pulse height depression". What occurs when the PHA peaks starts to shift lower (at higher count rates) or shifts higher (at lower count rates), is not "instability" but rather "non-linearity". This is exactly why people seem to think that they need to "count rate match" their standard and unknown, but it is simply not necessary as long as one sets their PHA gain or bias high enough so that the PHA peak is *completely* above the baseline level
at the highest count rate that one expects to measure (usually the highest concentration (primary std) at the highest beam current to be utilized).
That is, as the PHA shifts higher or lower, the baseline either cuts off pulse counts or includes more pulse counts from the left side tail of the PHA peak, thus introducing a non-linear response as a function of count rate.
Paul then mentions this: "Avoid tight PHA window, use integral mode unless a PHA interference is observed." But I would modify this to say: Because the use of PHA differential mode does not help with same Bragg order interferences, instead allow all interferences (same or higher order) to be counted and deal with the interferences properly using the quantitative interference correction.
I say this because, even in the case of higher order interferences, one cannot be sure that the interference pulses are cleanly separated from the interfered pulses.
It is far better to obtain a linear response from our detectors/counting electronics and deal with any interference corrections in software. The one exception I can think of is maybe analyzing trace oxygen in a Na compound because it's difficult to find a material containing a known amount of Na but no oxygen, for use as an interference standard!
Here's an example from a week ago where we analyzed PbSiO3 (natural Alamosite assumed stoichiometry) using SiO2 as the primary standard. Here are the results for all 11 matrix corrections:
Summary of All Calculated (averaged) Matrix Corrections:
St 386 Set 8 Alamosite (PbSiO3)
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Mn Fe Pb O TOTAL
1 10.370 -.013 -.005 .011 73.151 16.939 100.454 Armstrong/Brown/Scott-Love (prZ)
2 9.228 -.010 -.005 .011 73.151 16.939 99.314 Philibert/Duncumb-Reed
3 9.691 -.011 -.005 .012 73.151 16.939 99.777 Heinrich/Duncumb-Reed
4 9.302 -.011 -.005 .011 73.151 16.939 99.388 Love-Scott I
5 9.423 -.011 -.005 .011 73.151 16.939 99.509 Love-Scott II
6 8.037 -.010 -.004 .010 73.151 16.939 98.123 Packwood Phi(prZ) (EPQ-91)
7 10.056 -.012 -.005 .012 73.151 16.939 100.141 Bastin (original) (prZ)
8 9.481 -.011 -.005 .011 73.151 16.939 99.566 Bastin PROZA Phi (prZ) (EPQ-91)
9 9.314 -.011 -.005 .011 73.151 16.939 99.399 Pouchou and Pichoir-Full (PAP)
10 9.146 -.011 -.005 .011 73.151 16.939 99.232 Pouchou and Pichoir-Simplified (XPP)
11 9.996 -.012 -.005 .011 73.151 16.939 100.080 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 9.459 -.011 -.005 .011 73.151 16.939 99.544
SDEV: .612 .001 .000 .000 .000 .000 .612
SERR: .185 .000 .000 .000 .000 .000
MIN: 8.037 -.013 -.005 .010 73.151 16.939 98.123
MAX: 10.370 -.010 -.004 .012 73.151 16.939 100.454
Percent Variances:
ELEM: Si Mg Mn Fe Pb O
PUBL: 9.910 n.a. n.a. n.a. 73.151 16.939
STDS: 14 12 25 395 --- ---
ELEM: Si Mg Mn Fe Pb O
1 4.65 --- --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 -6.88 --- --- --- --- --- Philibert/Duncumb-Reed
3 -2.21 --- --- --- --- --- Heinrich/Duncumb-Reed
4 -6.13 --- --- --- --- --- Love-Scott I
5 -4.91 --- --- --- --- --- Love-Scott II
6 -18.90 --- --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 1.47 --- --- --- --- --- Bastin (original) (prZ)
8 -4.33 --- --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 -6.01 --- --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 -7.71 --- --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 .87 --- --- --- --- --- Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: -4.55 .00 .00 .00 .00 .00
SDEV: 6.18 .00 .00 .00 .00 .00
SERR: 1.86 .00 .00 .00 .00 .00
MIN: -18.90 .00 .00 .00 .00 .00
MAX: 4.65 .00 .00 .00 .00 .00
That's pretty wild, right?
Note the magnitude of the atomic number correction (from DebugMode in PFE or CalcZAF), for the last data point:
SAMPLE: 2545, ITERATIONS: 3, Z-BAR: 48.30882
ELEMENT ABSCOR FLUCOR ZEDCOR ZAFCOR STP-POW BKS-COR F(x)u Ec Eo/Ec MACs STDNUM uZAF/sZAF
Si ka 1.6104 .9949 .7741 1.2402 .6403 1.2089 .5346 1.8390 10.8755 1355.02 14 1.0382
Mg ka 2.4771 1.0000 .7735 1.9161 .6260 1.2358 .3264 1.3050 15.3257 2742.98 12 1.3592
Mn ka 1.1342 1.0000 .8759 .9935 .8040 1.0894 .8562 6.5390 3.0586 356.758 25 .95158
Fe ka 1.1032 .9854 .8580 .9327 .7936 1.0811 .8833 7.1120 2.8121 289.657 395 .88853
ELEMENT K-RAW K-RATIO ELEMWT% OXIDWT% ATOMIC% FORMULA TAKEOFF KILOVOL
Si ka .20530 .08033 9.962 ----- 20.085 .000 40.00 20.00
Mg ka -.00019 -.00008 -.016 ----- -.037 .000 40.00 20.00
Mn ka -.00008 -.00006 -.006 ----- -.006 .000 40.00 20.00
Fe ka .00024 .00016 .015 ----- .015 .000 40.00 20.00
Pb 73.151 ----- 19.993 .000
O 16.939 ----- 59.950 .000
TOTAL: 100.045 ----- 100.000 .000
And here for those interested are the analysis for all data points using the Armstrong/Donovan and Moy matrix correction:
St 386 Set 8 Alamosite (PbSiO3)
TakeOff = 40.0 KiloVolt = 20.0 Beam Current = 30.0 Beam Size = 10
(Magnification (analytical) = 20000), Beam Mode = Analog Spot
(Magnification (default) = 1000, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
Tsumeb, South West Africa
From Mineralogical Research, CA
(assumed stoichiometric)
Number of Data Lines: 6 Number of 'Good' Data Lines: 6
First/Last Date-Time: 04/19/2026 10:56:41 PM to 04/19/2026 11:08:42 PM
Average Total Oxygen: .000 Average Total Weight%: 100.080
Average Calculated Oxygen: .000 Z-Bar (Z Fraction^0.7): 48.289
Average Excess Oxygen: .000 Average Atomic Weight: 56.630
Average ZAF Iteration: 3.00 Average Quant Iterate: 2.00
St 386 Set 8 Alamosite (PbSiO3), Results in Elemental Weight Percents
ELEM: Si Mg Mn Fe Pb O
TYPE: ANAL ANAL ANAL ANAL SPEC SPEC
BGDS: LIN LIN LIN LIN
TIME: 60.00 60.00 60.00 60.00 --- ---
BEAM: 29.88 29.88 29.88 29.88 --- ---
ELEM: Si Mg Mn Fe Pb O SUM
2540 10.013 -.014 -.001 .008 73.151 16.939 100.096
2541 10.000 -.007 -.011 .011 73.151 16.939 100.083
2542 10.020 -.009 -.001 .009 73.151 16.939 100.109
2543 10.001 -.020 -.005 .009 73.151 16.939 100.074
2544 9.982 -.009 -.003 .014 73.151 16.939 100.074
2545 9.962 -.016 -.006 .015 73.151 16.939 100.045
AVER: 9.996 -.012 -.005 .011 73.151 16.939 100.080
SDEV: .021 .005 .004 .003 .000 .000 .022
SERR: .009 .002 .001 .001 .000 .000
%RSD: .21 -38.89 -76.31 27.89 .00 .00
PUBL: 9.910 n.a. n.a. n.a. 73.151 16.939 100.000
%VAR: .87 --- --- --- --- ---
DIFF: .086 --- --- --- --- ---
STDS: 14 12 25 395 --- ---
STKF: .3913 .4276 .7418 .6867 --- ---
STCT: 2304.52 745.26 466.57 1036.19 --- ---
UNKF: .0806 -.0001 .0000 .0001 --- ---
UNCT: 474.75 -.11 -.03 .18 --- ---
UNBG: 11.48 1.53 1.62 5.04 --- ---
ZCOR: 1.2402 1.9158 .9936 .9328 --- ---
KRAW: .2060 -.0002 -.0001 .0002 --- ---
PKBG: 42.37 .93 .98 1.04 --- ---
Here's your 1% EPMA accuracy from pure oxide primary standards post of the day!
Si Ka in albite using SiO2 as a primary standard:
(https://smf.probesoftware.com/gallery/395_28_04_26_9_27_34.png)
Yes, this albite is a natural specimen, but it was assumed stoichiometric minus the traces... now here is Al Ka in the same albite, using Al2O3 as the primary standard:
(https://smf.probesoftware.com/gallery/395_28_04_26_9_28_38.png)
This is good because Will Nachlas will probably be using a natural (alpine) albite from Julien Allaz for the FIGMAS standard mount. This albite might be the only natural mineral in the FIGMAS mount because there doesn't seem to be any synthetic (beam stable and water insoluble) Na minerals commercially available.
Unless anyone knows of something?
Now let's look at accuracy when measuring Ti Ka extrapolating from TiO2 at 15 and 20 keV. Let's start with SrTiO3:
(https://smf.probesoftware.com/gallery/395_30_04_26_12_55_10.png)
All points close to 1% relative accuracy! Now for RbTiOPO4 again at 15 and 20 keV:
(https://smf.probesoftware.com/gallery/395_30_04_26_12_55_33.png)
Again, very close to 1% accuracy!
I'm sure many of you have synthetic TiO2 and SrTiO3 materials, and I'll bet a few of you have RbTiOPO4, which by the way can be obtained from Marc Schier for $100 a gram:
https://calchemist.com/
and makes a wonderful Rb standard and is completely beam stable. So what are you waiting for? Just be sure to tune your PHAs properly. Here's what Andrew and I used for these measurements:
(https://smf.probesoftware.com/gallery/395_30_04_26_12_55_59.png)
Note that the PHA peak is completely above the baseline level. Yes, we had to amplify the detector a bit to get this accomplished, but with this gain/bias setting and in PHA integral mode, you will get 1% accuracy on suitable standards extrapolating from pure synthetic oxides!
More "breaking the EPMA 1% accuracy barrier" of the day. Here's Si Ka measured in natural diopside (assumed stoichiometry minus traces) extrapolated from SiO2:
(https://smf.probesoftware.com/gallery/395_01_05_26_11_26_58.png)
and here is Mg Ka extrapolated from the MgO primary std:
(https://smf.probesoftware.com/gallery/395_01_05_26_11_27_27.png)
Wouldn't it be nice if every EPMA lab in the world were using the same synthetic SiO2, MgO, Fe3O4, TiO2, Al2O3, etc., primary standards? And we could check them against secondary standards such as synthetic MgAl2O4, Mg2SiO4, SrTiO3, etc?
That is exactly what Will Nachlas is working towards... hopefully he can give us an update on his global FIGMAS mount.
Quote from: wonachlas on November 22, 2021, 09:02:30 AMThe Focused Interest Group on MicroAnalytical Standards (FIGMAS), a FIG of the Microscopy Society of America (MSA) and co-sponsored by the Microanalysis Society (MAS), is organizing a series of round robin exercises to begin investigating synthetic standard materials for developing a universal standards mount and accompanying database of community k-ratios. Details of the round robin and a survey to express interest are included in the link below. All labs who meet the stated criteria are welcome to participate.
https://docs.google.com/forms/d/e/1FAIpQLSd8nttQYcex9UmnHJyD3iHE-vpL7gG5XVpNumX8-fqrWrgb9A/viewform
Continuing with our "Limits of EPMA Accuracy" posts, here are analyses of NIST K-412 mineral glass analyzed using MgO and SiO2 as primary standards. First Mg Ka:
(https://smf.probesoftware.com/gallery/395_05_05_26_1_09_11.png)
Around 1% accuracy extrapolating from pure oxide primary standards. Now for Si ka:
(https://smf.probesoftware.com/gallery/395_05_05_26_1_09_39.png)
Better than 1% accuracy at both 15 and 20 keV!
This is doable using the constant k-ratio dead time calibrations, aligned spectrometers, properly tuned PHA settings, and the Donovan and Moy matrix correction with FFAST MACs!
Following up with NIST SRM K-412 we have Fe Ka extrapolated from Fe3O4:
(https://smf.probesoftware.com/gallery/395_11_05_26_2_54_30.png)
Again, ~1% relative accuracy. Now for Al Ka:
(https://smf.probesoftware.com/gallery/395_11_05_26_2_55_05.png)
Now this is interesting. At 15 keV we are close, ~1% accuracy, but at 20 keV (in the middle) we are off by ~4%, though that's only an absolute difference of 0.2 wt%:
St 160 Set 2 NBS K-412 mineral glass
TakeOff = 40.0 KiloVolt = 20.0 Beam Current = 30.0 Beam Size = 10
(Magnification (analytical) = 20000), Beam Mode = Analog Spot
(Magnification (default) = 1000, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
SRM 470, NIST
C.M. Taylor (Photometry?) FeO 2.77, Fe2O3 8.15
Total as FeO 10.10, Excess O 0.815
Na = 430 PPM (EPMA by JJD)
Number of Data Lines: 6 Number of 'Good' Data Lines: 6
First/Last Date-Time: 04/25/2026 05:36:42 PM to 04/25/2026 05:49:20 PM
Average Total Oxygen: .000 Average Total Weight%: 100.253
Average Calculated Oxygen: .000 Z-Bar (Z Fraction^0.7): 12.035
Average Excess Oxygen: .000 Average Atomic Weight: 21.987
Average ZAF Iteration: 4.00 Average Quant Iterate: 2.00
St 160 Set 2 NBS K-412 mineral glass, Results in Elemental Weight Percents
ELEM: Si Mg Fe Al Ti Ca Mn O
TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC
BGDS: LIN LIN LIN LIN LIN
TIME: 60.00 60.00 60.00 60.00 60.00 --- --- ---
BEAM: 29.86 29.86 29.86 29.86 29.86 --- --- ---
ELEM: Si Mg Fe Al Ti Ca Mn O SUM
721 21.176 11.703 7.790 5.115 .000 10.899 .077 43.597 100.357
722 21.148 11.671 7.748 5.085 -.001 10.899 .077 43.597 100.224
723 21.189 11.676 7.739 5.112 .008 10.899 .077 43.597 100.298
724 21.158 11.712 7.773 5.086 -.002 10.899 .077 43.597 100.300
725 21.130 11.661 7.699 5.122 -.003 10.899 .077 43.597 100.181
726 21.100 11.646 7.712 5.117 .008 10.899 .077 43.597 100.157
AVER: 21.150 11.678 7.743 5.106 .002 10.899 .077 43.597 100.253
SDEV: .032 .025 .035 .016 .005 .000 .000 .000 .078
SERR: .013 .010 .014 .007 .002 .000 .000 .000
%RSD: .15 .21 .45 .32 308.92 .00 .00 .00
PUBL: 21.199 11.657 7.742 4.906 n.a. 10.899 .077 43.597 100.077
%VAR: -.23 .18 .02 4.08 --- --- --- ---
DIFF: -.049 .021 .001 .200 --- --- --- ---
STDS: 14 3012 395 3013 22 --- --- ---
STKF: .3913 .4281 .6867 .4056 .5626 --- --- ---
STCT: 2263.58 751.78 1072.35 948.82 169.10 --- --- ---
UNKF: .1422 .0649 .0668 .0295 .0000 --- --- ---
UNCT: 822.93 114.02 104.35 69.05 .00 --- --- ---
UNBG: 4.41 .71 1.42 .92 .14 --- --- ---
ZCOR: 1.4869 1.7986 1.1589 1.7298 1.1913 --- --- ---
KRAW: .3636 .1517 .0973 .0728 .0000 --- --- ---
PKBG: 187.44 160.90 74.60 75.86 1.03 --- --- ---
Interestingly all the matrix corrections are off for Al at 20 keV, some over and some under (except for Packwood, and then, all the other elements are off by 3 to 4%!):
Summary of All Calculated (averaged) Matrix Corrections:
St 160 Set 2 NBS K-412 mineral glass
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Fe Al Ti Ca Mn O TOTAL
1 21.151 11.673 7.752 5.104 .002 10.899 .077 43.597 100.256 Armstrong/Brown/Scott-Love (prZ)
2 21.127 11.461 7.940 5.065 .002 10.899 .077 43.597 100.167 Philibert/Duncumb-Reed
3 21.222 11.591 7.680 5.110 .002 10.899 .077 43.597 100.178 Heinrich/Duncumb-Reed
4 21.291 11.696 7.763 5.142 .002 10.899 .077 43.597 100.467 Love-Scott I
5 21.213 11.714 7.760 5.128 .002 10.899 .077 43.597 100.390 Love-Scott II
6 20.469 11.301 8.024 4.924 .002 10.899 .077 43.597 99.293 Packwood Phi(prZ) (EPQ-91)
7 21.135 11.651 7.798 5.044 .002 10.899 .077 43.597 100.203 Bastin (original) (prZ)
8 21.320 11.724 7.906 5.152 .002 10.899 .077 43.597 100.677 Bastin PROZA Phi (prZ) (EPQ-91)
9 21.227 11.679 7.894 5.131 .002 10.899 .077 43.597 100.506 Pouchou and Pichoir-Full (PAP)
10 21.066 11.586 7.905 5.077 .002 10.899 .077 43.597 100.209 Pouchou and Pichoir-Simplified (XPP)
11 21.150 11.678 7.743 5.106 .002 10.899 .077 43.597 100.253 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 21.125 11.614 7.833 5.089 .002 10.899 .077 43.597 100.236
SDEV: .230 .129 .106 .064 .000 .000 .000 .000 .353
SERR: .069 .039 .032 .019 .000 .000 .000 .000
MIN: 20.469 11.301 7.680 4.924 .002 10.899 .077 43.597 99.293
MAX: 21.320 11.724 8.024 5.152 .002 10.899 .077 43.597 100.677
Percent Variances:
ELEM: Si Mg Fe Al Ti Ca Mn O
PUBL: 21.199 11.657 7.742 4.906 n.a. 10.899 .077 43.597
STDS: 14 3012 395 3013 22 --- --- ---
ELEM: Si Mg Fe Al Ti Ca Mn O
1 -.23 .14 .14 4.03 --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 -.34 -1.68 2.56 3.24 --- --- --- --- Philibert/Duncumb-Reed
3 .11 -.57 -.80 4.15 --- --- --- --- Heinrich/Duncumb-Reed
4 .43 .34 .27 4.81 --- --- --- --- Love-Scott I
5 .07 .49 .24 4.52 --- --- --- --- Love-Scott II
6 -3.44 -3.06 3.65 .37 --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 -.30 -.05 .73 2.82 --- --- --- --- Bastin (original) (prZ)
8 .57 .58 2.12 5.01 --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 .13 .19 1.97 4.58 --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 -.63 -.61 2.10 3.48 --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 -.23 .18 .02 4.08 --- --- --- --- Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: -.35 -.37 1.18 3.74 .00 .00 .00 .00
SDEV: 1.08 1.10 1.36 1.30 .00 .00 .00 .00
SERR: .33 .33 .41 .39 .00 .00 .00 .00
MIN: -3.44 -3.06 -.80 .37 .00 .00 .00 .00
MAX: .57 .58 3.65 5.01 .00 .00 .00 .00
The Fe result for the Donovan and Moy correction is also very impressive.
Looking at the 15 keV data, yes, Al is off by ~1.4% relative, but that's only a difference of 700 PPM!
St 160 Set 1 NBS K-412 mineral glass
TakeOff = 40.0 KiloVolt = 15.0 Beam Current = 30.0 Beam Size = 10
(Magnification (analytical) = 20000), Beam Mode = Analog Spot
(Magnification (default) = 1000, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
SRM 470, NIST
C.M. Taylor (Photometry?) FeO 2.77, Fe2O3 8.15
Total as FeO 10.10, Excess O 0.815
Na = 430 PPM (EPMA by JJD)
Number of Data Lines: 6 Number of 'Good' Data Lines: 6
First/Last Date-Time: 04/25/2026 01:30:21 PM to 04/25/2026 01:42:59 PM
Average Total Oxygen: .000 Average Total Weight%: 100.133
Average Calculated Oxygen: .000 Z-Bar (Z Fraction^0.7): 12.033
Average Excess Oxygen: .000 Average Atomic Weight: 21.981
Average ZAF Iteration: 4.00 Average Quant Iterate: 2.00
St 160 Set 1 NBS K-412 mineral glass, Results in Elemental Weight Percents
ELEM: Si Mg Fe Al Ti Ca Mn O
TYPE: ANAL ANAL ANAL ANAL ANAL SPEC SPEC SPEC
BGDS: LIN LIN LIN LIN LIN
TIME: 60.00 60.00 60.00 60.00 60.00 --- --- ---
BEAM: 30.07 30.07 30.07 30.07 30.07 --- --- ---
ELEM: Si Mg Fe Al Ti Ca Mn O SUM
625 21.314 11.603 7.704 4.999 -.006 10.899 .077 43.597 100.187
626 21.295 11.556 7.679 4.950 .002 10.899 .077 43.597 100.055
627 21.317 11.573 7.690 4.978 .005 10.899 .077 43.597 100.137
628 21.343 11.616 7.697 5.013 -.004 10.899 .077 43.597 100.239
629 21.287 11.542 7.723 4.937 .007 10.899 .077 43.597 100.069
630 21.299 11.543 7.718 4.977 -.001 10.899 .077 43.597 100.110
AVER: 21.309 11.572 7.702 4.976 .001 10.899 .077 43.597 100.133
SDEV: .020 .031 .017 .029 .005 .000 .000 .000 .071
SERR: .008 .013 .007 .012 .002 .000 .000 .000
%RSD: .09 .27 .22 .57 734.52 .00 .00 .00
PUBL: 21.199 11.657 7.742 4.906 n.a. 10.899 .077 43.597 100.077
%VAR: .52 -.73 -.52 1.42 --- --- --- ---
DIFF: .110 -.085 -.040 .070 --- --- --- ---
STDS: 14 3012 395 3013 22 --- --- ---
STKF: .4129 .4791 .6790 .4399 .5564 --- --- ---
STCT: 1650.58 634.29 492.16 768.23 90.08 --- --- ---
UNKF: .1648 .0783 .0654 .0344 .0000 --- --- ---
UNCT: 658.65 103.70 47.39 60.14 .00 --- --- ---
UNBG: 3.77 .63 .84 .83 .09 --- --- ---
ZCOR: 1.2934 1.4774 1.1781 1.4449 1.1800 --- --- ---
KRAW: .3990 .1635 .0963 .0783 .0000 --- --- ---
We reproduced the Mg and Si analyses in Mg2SiO4:
https://smf.probesoftware.com/index.php?topic=1831.msg14120#msg14120
and got very similar results as before:
(https://smf.probesoftware.com/gallery/395_22_05_26_2_00_35.png)
for Mg Ka within 1% at both 15 and 20 keV, and for Si Ka within 1% for 15 keV, but only within 2% at 20 keV:
(https://smf.probesoftware.com/gallery/395_22_05_26_1_58_09.png)
At 15 keV, both Armstrong/Brown matrix corrections do better than PAP:
Summary of All Calculated (averaged) Matrix Corrections:
St 273 Set 3 Mg2SiO4 (magnesium olivine) synthetic
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Fe Al Ti O TOTAL
1 20.038 34.423 .004 .004 .004 45.486 99.959 Armstrong/Brown/Scott-Love (prZ)
2 20.436 34.361 .004 .004 .005 45.486 100.295 Philibert/Duncumb-Reed
3 20.324 34.509 .004 .004 .004 45.486 100.332 Heinrich/Duncumb-Reed
4 20.149 34.444 .004 .004 .004 45.486 100.091 Love-Scott I
5 20.028 34.413 .004 .004 .004 45.486 99.939 Love-Scott II
6 19.929 34.315 .004 .004 .005 45.486 99.743 Packwood Phi(prZ) (EPQ-91)
7 20.258 34.417 .004 .004 .004 45.486 100.173 Bastin (original) (prZ)
8 20.410 34.513 .004 .004 .005 45.486 100.421 Bastin PROZA Phi (prZ) (EPQ-91)
9 20.303 34.482 .004 .004 .005 45.486 100.284 Pouchou and Pichoir-Full (PAP)
10 20.211 34.442 .004 .004 .005 45.486 100.152 Pouchou and Pichoir-Simplified (XPP)
11 20.046 34.422 .004 .004 .004 45.486 99.967 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 20.194 34.431 .004 .004 .004 45.486 100.123
SDEV: .169 .059 .000 .000 .000 .000 .205
SERR: .051 .018 .000 .000 .000 .000
MIN: 19.929 34.315 .004 .004 .004 45.486 99.743
MAX: 20.436 34.513 .004 .004 .005 45.486 100.421
Percent Variances:
ELEM: Si Mg Fe Al Ti O
PUBL: 19.960 34.554 n.a. n.a. n.a. 45.486
STDS: 14 3012 395 3013 22 ---
ELEM: Si Mg Fe Al Ti O
1 .39 -.38 --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 2.38 -.56 --- --- --- --- Philibert/Duncumb-Reed
3 1.82 -.13 --- --- --- --- Heinrich/Duncumb-Reed
4 .95 -.32 --- --- --- --- Love-Scott I
5 .34 -.41 --- --- --- --- Love-Scott II
6 -.15 -.69 --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 1.49 -.40 --- --- --- --- Bastin (original) (prZ)
8 2.25 -.12 --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 1.72 -.21 --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 1.26 -.33 --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 .43 -.38 --- --- --- --- Armstrong/Donovan and Moy BSC/BKS (prZ)
But at 20 keV, both Armstrong methods seem to do a bit worse for Si Ka in Mg2SiO4:
Summary of All Calculated (averaged) Matrix Corrections:
St 273 Set 2 Mg2SiO4 (magnesium olivine) synthetic
FFAST Chantler (NIST v 2.1, 2005)
Elemental Weight Percents:
ELEM: Si Mg Fe Al Ti O TOTAL
1 19.616 34.466 .003 .001 -.002 45.486 99.571 Armstrong/Brown/Scott-Love (prZ)
2 19.831 34.359 .003 .001 -.002 45.486 99.678 Philibert/Duncumb-Reed
3 19.740 34.499 .003 .001 -.002 45.486 99.727 Heinrich/Duncumb-Reed
4 19.982 34.536 .003 .001 -.002 45.486 100.006 Love-Scott I
5 19.762 34.505 .003 .001 -.002 45.486 99.755 Love-Scott II
6 19.407 34.332 .003 .001 -.002 45.486 99.227 Packwood Phi(prZ) (EPQ-91)
7 19.931 34.500 .003 .001 -.002 45.486 99.920 Bastin (original) (prZ)
8 20.094 34.568 .003 .001 -.002 45.486 100.151 Bastin PROZA Phi (prZ) (EPQ-91)
9 20.066 34.556 .003 .001 -.002 45.486 100.111 Pouchou and Pichoir-Full (PAP)
10 19.833 34.483 .003 .001 -.002 45.486 99.804 Pouchou and Pichoir-Simplified (XPP)
11 19.630 34.467 .003 .001 -.002 45.486 99.585 Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: 19.809 34.479 .003 .001 -.002 45.486 99.776
SDEV: .208 .074 .000 .000 .000 .000 .268
SERR: .063 .022 .000 .000 .000 .000
MIN: 19.407 34.332 .003 .001 -.002 45.486 99.227
MAX: 20.094 34.568 .003 .001 -.002 45.486 100.151
Percent Variances:
ELEM: Si Mg Fe Al Ti O
PUBL: 19.960 34.554 n.a. n.a. n.a. 45.486
STDS: 14 3012 395 3013 22 ---
ELEM: Si Mg Fe Al Ti O
1 -1.72 -.25 --- --- --- --- Armstrong/Brown/Scott-Love (prZ)
2 -.65 -.57 --- --- --- --- Philibert/Duncumb-Reed
3 -1.10 -.16 --- --- --- --- Heinrich/Duncumb-Reed
4 .11 -.05 --- --- --- --- Love-Scott I
5 -.99 -.14 --- --- --- --- Love-Scott II
6 -2.77 -.64 --- --- --- --- Packwood Phi(prZ) (EPQ-91)
7 -.14 -.16 --- --- --- --- Bastin (original) (prZ)
8 .67 .04 --- --- --- --- Bastin PROZA Phi (prZ) (EPQ-91)
9 .53 .01 --- --- --- --- Pouchou and Pichoir-Full (PAP)
10 -.64 -.21 --- --- --- --- Pouchou and Pichoir-Simplified (XPP)
11 -1.66 -.25 --- --- --- --- Armstrong/Donovan and Moy BSC/BKS (prZ)
AVER: -.76 -.22 .00 .00 .00 .00
SDEV: 1.04 .21 .00 .00 .00 .00
SERR: .31 .06 .00 .00 .00 .00
MIN: -2.77 -.64 .00 .00 .00 .00
MAX: .67 .04 .00 .00 .00 .00
Though Mg Ka looks great.
Re-running Mg Ka and Al Ka on our MgAl2O4 synthetic using MgO and Al2O3 as primary standards we obtain this for Mg Ka:
(https://smf.probesoftware.com/gallery/395_28_05_26_1_44_23.png)
Both 15 and 20 (center) keV analyses are close to 1% relative accuracy. Here for Al Ka:
(https://smf.probesoftware.com/gallery/395_28_05_26_1_43_17.png)
Again, close to 1% relative accuracy extrapolating from pure oxide primary standards.
Here are the full set of analyses at 15 and 20 keV for the Si Ka in PbSiO3 extrapolated from SiO2 as the primary standard, I showed previously:
https://smf.probesoftware.com/index.php?topic=1831.msg14152#msg14152
(https://smf.probesoftware.com/gallery/395_31_05_26_9_55_58.png)
It's interesting that the 15 keV analyses are all around ~1% low and the 20 keV analyses are all around 1% high.
Does that mean if we ran them again at 18 keV, they would be even better accuracy? I think I will try doing another run with a range of keVs and plotting accuracy vs keV when I get a chance!
Just a quick note that we've added a new menu under the Probe for EPMA Help menu on tuning PHA settings for best accuracy that links to a pdf:
(https://smf.probesoftware.com/gallery/1_03_06_26_5_30_29.png)
Right now this pdf only has examples for Cameca EPMA instruments, so we would very much appreciate any screen captures of PHA scans for JEOL instruments tuned in a similar manner to the spec 3 LLIF at high currents.
Update PFE from the Help menu to see this most recent document.
The recent improvements in Probe-for-EPMA are impressive, particularly in the areas of matrix corrections, background fitting and the resultant accuracy.
However, I suggest that matrix matching, where possible can still provide slight improvements in accuracy.
As an example I provide actual average analyses of troilite, alabandite, and pyrite, using two different standards for the Fe and S - pyrrhotite (Fe7S8) and marcasite (FeS2).
(https://smf.probesoftware.com/gallery/406_04_06_26_12_31_41.jpeg)
(or attached PDF)
For troilite and alabandite, the Fe & S standard that gives the best results is pyrrhotite.
(Admittedly, the differences for alabandite are trivial).
Whereas for pyrite, the Fe & S standard that gives the best results is marcasite.
In these analyses, it is iron that is most affected by the choice of standard.
Because of this behavior, matrix matching for Fe is still an improvement in this system.
Cheers, Andrew
Quote from: AndrewLocock on June 04, 2026, 12:41:54 PMThe recent improvements in Probe-for-EPMA are impressive, particularly in the areas of matrix corrections, background fitting and the resultant accuracy.
However, I suggest that matrix matching, where possible can still provide slight improvements in accuracy.
Thanks! It would also be nice to see some percent relative errors for these analyses...
Yes, I completely agree that "matrix matching" ones standard to ones unknown, can minimize the matrix correction. But the real problem I think that so called "matrix matching" is addressing is not really the matrix correction,
but rather it is "count rate matching".
Because using a standard with a similar matrix means the concentrations are probably similar, and therefore the count rates are also similar. Therefore "count rate matching" also minimizes the dead time correction and makes pulse height depression less of an issue, so that helps when count rates differ between the standard and the unknown.
This, I think, is the real reason many analysts are selecting a standard with a similar matrix to their unknown!The other problem is whether the "matrix matched" standard one selects is actually what it is claimed to be. For example, is the assumed stoichiometry of pyrrhotite actually what it is? We know that the natural San Carlos olivine (even when sourced from the Smithsonian) has a significantly variable composition as reported by John Fournelle and others. Which we suspect explains why various EPMA labs around the world report reproducible
intra-lab results, but consistently different
inter-lab results (see Wieser et al, Barometers behaving badly, 2023). So much so that geologists have taken to creating laboratory "correction factors" for each lab! Is this really what we want?
https://smf.probesoftware.com/index.php?topic=1831.msg13974#msg13974
What we need are globally distributed high purity end member synthetic minerals, but also have our instrument well calibrated so they can handle standards and unknowns with very different count rates.
Look, I get it. If one performs the dead time, Bragg order k-ratio calibrations and the PHA integral-baseline tuning method I have suggested in this topic, one could use high purity synthetic MgO as a Mg Ka standard for analyzing olivines, but one could also use a high purity synthetic Mg2SiO4. And you know what? Both will be included in the FIGMAS mount that Will Nachlas is putting together with support from MAS. Because then we can measure k-ratio consensus (consensi?) between labs, once these mounts are distributed globally!
As stated above, the real reason I think that many users find "matrix matched" standards to be superior, is because they are actually "count rate matching" to their unknowns. Why is this? Because their dead time constants are not calibrated properly and they are not using the integral baseline PHA tuning method (described above) to obtain a linear response from their electronics. So they *have* to use "count rate matched" standards, even when we know they are heterogeneous from grain to grain.
Does anyone remember when Gene Jarosewich said that if you use the Smithsonian mineral standards you should average at least 10 grams for standardizing to obtain an accurate comparison to his wet chemistry? Does *anyone* do that? No, they use their "favorite" grain...
The more important question is, have they run the constant k-ratio dead time calibration method on their instruments? Probably not. See the pdf in the Help menu of Probe for EPMA and here:
https://smf.probesoftware.com/index.php?topic=1466.msg11102#msg11102
Have they checked their effective take off angles? (Though probably not a major issue for Fe ka!) See the pdf in the Help menu of Probe for EPMA and here:
https://smf.probesoftware.com/index.php?topic=1739.0
Also, have they tried the integral baseline PHA tuning method? Again see the pdf in the Help menu of the latest Probe for EPMA version as discussed in the post above. This integral baseline PHA tuning method allows one to have vastly different count rates between their standard and their unknown and still achieve ~1% relative accuracy. For example:
(https://smf.probesoftware.com/gallery/395_05_06_26_7_14_46.png)
Yes, the new backscatter loss matrix correction method works really well, as do the FFAST MACs, but these are just part of the problem of why different labs are consistently reporting different results for the same materials and I think "matrix matched" heterogeneous natural standards is part of the problem.
Let's start with some k-ratio calibrations and get this sorted out by "failure" testing our instrument calibrations by extrapolating from a high purity synthetic primary standard to a much different secondary standard. Fe metal to pyrite might be good if we can assume the pyrite material is stoichiometric.
MgO to NIST glass is another good extrapolation... I've posted many other examples in this topic.
Here's a plot of S Ka in ZnS using FeS2 as a primary standard over a range of keVs for three different analytical models:
(https://smf.probesoftware.com/gallery/395_10_06_26_11_14_36.png)
Some of you may be wondering why we haven't shown any accuracy tests using a JEOL instrument, with the new PHA tuning method described here:
https://smf.probesoftware.com/index.php?topic=1854.msg14402#msg14402
I did finally recruit a JEOL expert (thanks to Emma Bullock!) and we were able to show that once the PHA peak for Fe ka was fully above the baseline level, the count rate remained the same even when we doubled the gain from 64 to 128 (see near the end of this long post):
https://smf.probesoftware.com/index.php?topic=1854.msg14406#msg14406
But, when we first attempted to analyze our NIST K-412 glass, we were low by ~3% relative! I was pretty dismayed by this result as you might imagine!
But then I noticed that Emma has chosen a magnetite standard that only had a 92% total as entered in the standard database (it was missing the excess oxygen), so I was starting to suspect that maybe this magnetite wasn't entered properly in the compositional database or that it wasn't as pure as it should be. So I asked Emma if she had another magnetite standard and she said she would do that.
So the next day she wrote and said she used their normal magnetite standard and the results were "much better". Well, "much better" is a bit of an understatement as it turns out!
St 44 Set 1 K412, Results in Elemental Weight Percents
ELEM: Fe Mg Al Si Ca O
TYPE: ANAL SPEC SPEC SPEC SPEC CALC
BGDS: LIN
TIME: 30.00 --- --- --- --- ---
BEAM: 19.97 --- --- --- --- ---
ELEM: Fe Mg Al Si Ca O SUM
104 7.696 11.657 4.911 21.198 10.899 43.560 99.921
105 7.770 11.657 4.911 21.198 10.899 43.581 100.016
106 7.779 11.657 4.911 21.198 10.899 43.584 100.027
107 7.685 11.657 4.911 21.198 10.899 43.557 99.906
108 7.800 11.657 4.911 21.198 10.899 43.590 100.054
AVER: 7.746 11.657 4.911 21.198 10.899 43.574 99.985
SDEV: .052 .000 .000 .000 .000 .015 .067
SERR: .023 .000 .000 .000 .000 .007
%RSD: .67 .00 .00 .00 .00 .03
PUBL: 7.742 11.657 4.911 21.198 10.899 43.573 99.980
%VAR: .05 --- --- --- --- ---
DIFF: .004 --- --- --- --- ---
STDS: 7 --- --- --- --- ---
STKF: .6820 --- --- --- --- ---
STCT: 472.79 --- --- --- --- ---
UNKF: .0657 --- --- --- --- ---
UNCT: 45.58 --- --- --- --- ---
UNBG: .82 --- --- --- --- ---
ZCOR: 1.1782 --- --- --- --- ---
KRAW: .0964 --- --- --- --- ---
PKBG: 56.59 --- --- --- --- ---
First of all I'll just say: 0.05% relative error isn't too bad! :D But I think we got a bit lucky cause this is just 5 points. So I'd like to see more measurements on JEOL instruments. Contact me off-line and I'm happy to walk you through this new PHA tuning producedure.
Using the new plot option of relative percent variance (i.e., accuracy) in Probe for EPMA from the Output | Plot Standard and Unknown XY plots menu dialog:
https://smf.probesoftware.com/index.php?topic=40.msg14388#msg14388
we can quickly evaluate our secondary standard accuracy. Here for Mg Ka in MgAl2O4 using MgO as a primary standard in the FIGMAS mount from Will Nachlas:
(https://smf.probesoftware.com/gallery/395_14_07_26_1_56_12.png)
All within 1% relative accuracy. But since we're plotting relative percent accuracy, we can plot more than a single compound, here Ti Ka in SrTiO3 and RbTiOPO4 using TiO2 as a primary standard:
(https://smf.probesoftware.com/gallery/395_14_07_26_1_56_32.png)
And here for Fe ka in a multitude of compounds using Fe metal as the primary standard for the sulfides, and magnetite as a primary standard for the oxides, silicates and glasses:
(https://smf.probesoftware.com/gallery/395_14_07_26_1_56_53.png)
Note that only the natural chromite is significantly outside the 1% variance accuracy limits.
In order to utilize the accuracy checks shown in the above plots, one must run their secondary standards as standard samples. Therefore, some of you have asked: how do I run my standards more than once?
Well first, to re-run ones standard samples a second time, just check the "Acquire Standard samples (again)" checkbox. Even if you don't have an unknown sample selected, the standards will run a second time.
To run your standard even more replicates, just create an unknown sample and check the Re-Standardization Interval checkbox and enter a short interval (in hours) as seen here:
(https://smf.probesoftware.com/gallery/1_15_07_26_2_21_35.png)
Say every hour or so. That's easy, right?