Hi Ben,
This is interesting. I ran some scans on my old SX50 on TiO2 and fluor-phlogopite and here is the scan on TiO2 on PC1 (I don't have a PC0 crystal):
(https://smf.probesoftware.com/gallery/395_13_09_17_12_22_40.png)
Looks very much like yours, no visible interference. Now here is a scan using the TAP crystal on the fluor-phlogopite:
(https://smf.probesoftware.com/gallery/395_13_09_17_12_22_59.png)
The peak shape is a bit funky probably because the TAP crystal is 30 years old! But it's at the peak position. Note that this is a pretty high precision scan because although I only ran at 15 keV, 20 nA, the count time per point was 80 secs.
Now here is another scan on the TAP crystal but this time on the TiO2 std:
(https://smf.probesoftware.com/gallery/395_13_09_17_12_23_15.png)
Whoa, so there is definitely an interference there and it doesn't look like a fluorine peak. I can't see what element could be however (Mo?). I'm going to run an EDS scan for a while and see if anything pops up that shouldn't be there...
Here is an EDS scan on my synthetic TiO2. Not much besides the Ti Ka/Kb (and sum peaks). A little Si and Al.
That tiny peak visible in the WDS is barely visible in the EDS spectrum as a change in slope where fluorine is. I wonder what it could be? I guess that just demonstrates how sensitive WDS is. And how sensitive MAN is to the background.
See attached (login to see attachments).
john
Hi John
Cool! Very interesting...
I am running some longer scans on my PC0 and TAP on my TiO2 again to see if I can replicate what you see. It must be there I guess, just that my scans were not long enough. Very quick google on manufacturing of TiO2 xtals, sounds like there can be a number of impurities depending of course on the starting material, but also on the type of manufacturing process. Just to list a few...
(Fe,Nb,Cr,Ta,V from starting materials, and Cl and/or S from some of the acidic manufacturing processes).
Looking at the positions of these relative to the F peak though, really only Ta matches up (sort of) peak position wise. Its a really obscure II order Ta intf though, and I would be surprised if there was enough Ta in the TiO2 to produce that intf...the test would be to do a wavescan over the Ta La (on LIF) position in the rutile (There is a III order intf of Ti on Ta Ma on TAP).
Will post my wavescans when its done.
Cheers
Hi John,
As requested. Here are two plots. The first includes std 140 Rutile. The second includes Mn metal and spessartine. I have noticed that Mn is the most significant thing to avoid when calibrating the MAN fit for F on our LDE1 crystal.
Cheers,
Malc.
Hi Malcolm
Thanks for that. Interesting! Your rutile std (140) also plots slightly above the fit. Would love to see the full list of standards you use in those plots as well. For a second I was about to scroll up/down in that standard list on the image...
Cheers
Hi Ben
That very much depends on the job. These plots come from two different packages. One for apatite and one for phylosilicates. The apatite run does not make use of the rutile standard for obvious reasons - we don't analyse Ti. However, there is a certain uniformity in what I get up to!!
Apatite run = 12 off = anhydrite, wilb ap, fluorite, magnetite, periclase, pyrope, tugtupite, wollastonite, dur ap, jadeite, mn metal, spessartine
bt, mus run = 21 off = wilb ap, barite, clinochlore, cr2O3, fluorite, magnetite, periclase, rutile, tugtupite, V metal, wollastonite, dur ap, corundum, jadeite, Mn metal, orthoclase, SC Ol, Kak pyrope, spessartine, biotite, muscovite.
Note.... I insert a bunch of things as refs as you might notice.
Cheers,
Malc.
Great, thanks for that Malcolm. Definitely some others in there I am going to try now and see how they go.
John, my scans on my TiO2 at F Ka peak position are attached for my LTAP and one of my other TAP xtals. I am impatient so only did 40sec count times, but the ?intf? peak is definitely there. Looking at it properly, it actually more lines up with Nb than Ta. But this is a higher order Nb IV interference. The element itself would make sense in a natural rutile given there is a niobian rutile end member. Perhaps the starting material for synthetic TiO2 isn't very pure.
The scan on my PC0 isn't finished yet.
Cheers
And the other thing I would like to raise is just how handy the MAN approach can be to dealing with interferences and such things. You will have seen Sobolev's work on trace elements in olivine. He runs up an elaborate technique to deal with Fe interference on Co, looking at counts at the Co peak position using Fe-only bearing standards and modifying the Co on peak counts off line. This interference cannot be dealt with simply by the usual correction procedure, but what Sobolev is doing (and may not know it) is simply a MAN background correction. if one sets up the MAN correction for Co in olivine using Fe only standards (Fe metal, pyrite, magnetite etc. etc) you can do precisely the same job at the press of a button. I'm not going to go into the utility of John's approach for traces....... It's pretty clear I think. The absolute flexibility of this approach to background correction is astounding if set up correctly and with sufficient forethought.
Lads.....
Just working on this new run for apatite. it's a more comprehensive thing involving some REE as well. Three plots: initial unplayed with, then including rutile (Ben ...interesting eh?), finally the working plot.
John... you might recall way back in the dark mists of time I suggested that a good addition might be to be able to specify Zed range rather than having to deselect standards from the list? Quite a lot of standards had to be deassigned to get me to the zed range I was interested in. Any chance something like this might be implemented??
Quote from: Malcolm Roberts on September 13, 2017, 06:41:15 PM
Hi John,
As requested. Here are two plots. The first includes std 140 Rutile. The second includes Mn metal and spessartine. I have noticed that Mn is the most significant thing to avoid when calibrating the MAN fit for F on our LDE1 crystal.
Cheers,
Malc.
Hi Malc,
Cool. So that is consistent with Ben's MAN plots in that there doesn't seem to be a problem with the LDE/PC crystals, just possibly the TAP crystals.
I suspect this is because the interfering line we saw in my TAP scan on Tio2 is a higher order reflection which are suppressed with the multi-layer Bragg crystals. I mean what element could it be if it's a first order reflection? I guess it could be fluorine except that the peak shift is quite large.
Do you have a TAP MAN curve for F ka with TiO2 (or Ti metal) that you can share?
Hi John
It would take an awful lot of digging around to find this. I abandoned TAP for F fairly early on as I was getting much better results from LDE1, e.g., higher on peak count rates and better LLD........
I'll see what I can find..
Watch this space.....
Cheers,
Malc.
Quote from: BenjaminWade on September 13, 2017, 07:25:54 PM
Great, thanks for that Malcolm. Definitely some others in there I am going to try now and see how they go.
John, my scans on my TiO2 at F Ka peak position are attached for my LTAP and one of my other TAP xtals. I am impatient so only did 40sec count times, but the ?intf? peak is definitely there. Looking at it properly, it actually more lines up with Nb than Ta. But this is a higher order Nb IV interference. The element itself would make sense in a natural rutile given there is a niobian rutile end member. Perhaps the starting material for synthetic TiO2 isn't very pure.
The scan on my PC0 isn't finished yet.
Cheers
Hi Ben,
Very cool that your natural TiO2 shows the same peak as my synthetic!
I guess there could be a trace Nb in my (our) TiO2. The EDS scan shows two tiny, tiny bumps at 2.1 and 2.2 keV, but they are very much in the noise.
We need to do a high precision wavescan of TiO2 at the Nb La region.
john
Quote from: Malcolm Roberts on September 13, 2017, 07:32:10 PM
And the other thing I would like to raise is just how handy the MAN approach can be to dealing with interferences and such things. You will have seen Sobolev's work on trace elements in olivine. He runs up an elaborate technique to deal with Fe interference on Co, looking at counts at the Co peak position using Fe-only bearing standards and modifying the Co on peak counts off line. This interference cannot be dealt with simply by the usual correction procedure, but what Sobolev is doing (and may not know it) is simply a MAN background correction. if one sets up the MAN correction for Co in olivine using Fe only standards (Fe metal, pyrite, magnetite etc. etc) you can do precisely the same job at the press of a button. I'm not going to go into the utility of John's approach for traces....... It's pretty clear I think. The absolute flexibility of this approach to background correction is astounding if set up correctly and with sufficient forethought.
Malcolm,
I think you have put your finger on it exactly.
That, and I would also note, this again reinforces Paul Carpenter's admonition that by using the MAN method, we learn things about our standards that we might never have suspected...
john
Hi John
As requested here are some plots for F on TAP. The first has everything. Note big problem with Cr. The second shows remaining bother from Mn and V. Note 828 is Kak hbl which has no F recorded in the database! I would remove it in real life of course!!
Yes Kakanui Hbd definitely has fluorine in it. With Fe and Mg intf on I still return anywhere from 500-1000 ppm in mine.
Latest on the mystery peak, definitely not Nb. Detailed wavescan at Nb La peak position on the rutile returns nothing, and given the size of the "intf" peak at F Ka peak position, if it was Nb it should be quite a reasonable peak.
The detailed wavescan at F peak position on rutile on PC0 also finished and is attached, but its confusing me. I don't see any interfering peak there at all like we do in the TAP scans, yet in my MAN fits for PC0 my rutile definitely sits above the fitted line, and those MAN fits were constructed using only peak counting times of 12 seconds, so I should definitely see it in the wavescan where it was 40 seconds per point? I am now thoroughly confused...
Although my Titanium metal is probably oxidised, I am going to run detailed scans on that as well to see if I see any peak on PC0/TAP. Given there isn't any problem with oxygen apparent from the rutile scans I am assuming my oxidised Ti metal will be OK...
Quote from: BenjaminWade on September 13, 2017, 11:56:59 PM
The detailed wavescan at F peak position on rutile on PC0 also finished and is attached, but its confusing me. I don't see any interfering peak there at all like we do in the TAP scans, yet in my MAN fits for PC0 my rutile definitely sits above the fitted line, and those MAN fits were constructed using only peak counting times of 12 seconds, so I should definitely see it in the wavescan where it was 40 seconds per point? I am now thoroughly confused...
Hi Ben,
The TiO2 in the F Ka MAN plots on PC1/PC0 don't look much like an outlier to me. Plot them with their error bars and see if you agree.
This makes some sense to me because, if the peak we are seeing is a higher order reflection, the multi-layer crystals will suppress their reflection. Whereas the TAP crystal reflects higher orders quite well.
john
Hmm I agree with your reasoning, but not sure if I would agree with the TiO2 being within error. Looking at the attached MAN plot with 3 sigma error bars, I think I would argue its definitely outside of error. Also if I now go back and have a look at all my other MAN fits, TiO2 is consistently systematically higher. Having said that I cannot explain why I can't see any peak in PC0 though....
I ran the wavescan on Ti metal (attached) and as you can see the peak is there but higher intensity. I guess we have to conclude that its probably a obscure Ti interference not in the database. I did end up running detailed wavescans over the Nb, Mo, Ta, W, Cd, P peak positions, but nothing there. I guess probably Nb would have been the only realistic option given that it can be many 1000's ppm in rutile.
The PC0 is till bugging me though. I might try some different MP acquisitions on TiO2 and see if I can measure it.
cheers
Quote from: BenjaminWade on September 14, 2017, 05:01:23 PM
Hmm I agree with your reasoning, but not sure if I would agree with the TiO2 being within error. Looking at the attached MAN plot with 3 sigma error bars, I think I would argue its definitely outside of error. Also if I now go back and have a look at all my other MAN fits, TiO2 is consistently systematically higher. Having said that I cannot explain why I can't see any peak in PC0 though....
I ran the wavescan on Ti metal (attached) and as you can see the peak is there but higher intensity. I guess we have to conclude that its probably a obscure Ti interference not in the database. I did end up running detailed wavescans over the Nb, Mo, Ta, W, Cd, P peak positions, but nothing there. I guess probably Nb would have been the only realistic option given that it can be many 1000's ppm in rutile.
The PC0 is till bugging me though. I might try some different MP acquisitions on TiO2 and see if I can measure it.
cheers
Hi Ben,
Awesome work- I was just making a (hopeful) guess on the PC1/PC0 MAN curves. I agree TiO2 still looks outside of the error range on PC0. But since the PC (and LDE) crystals do suppress higher order relfections, the peak may still be there, just much lower in intensity than TAP. And indeed TiO2 is a higher outlier on the TAP MAN plots...
Note that I ran my wavescans at 80 sec because one often acquires say 3 or 4 points on each MAN standard and if one is using a 20 sec count time that is pretty high precision (the MAN intensities are the average of all points in each MAN standard). Did you run your wavescan on TiO2 (or Ti) using PC0/PC1 with that sort of precision?
OK, this is interesting. If I look at the x-ray database table in CalcZAF and increase the order limit to 20th order reflections I *do* see a Ti Kb1 and Kb3 lines, but *below* F Ka (not above as we are observing). But this table isn't corrected for refractive index of the Bragg crystal, as it is in the PFE Plot! window!
Alas, if we plot the F Ka in TiO2 on TAP data with the Ti KLM markers on:
(https://smf.probesoftware.com/gallery/395_14_09_17_5_48_17.png)
So the mystery emission line does not reveal its true identity easily! Who will solve this conundrum? :D
john
Hi John
Yes you are right, I forgot the MAN point is the average of my 4 repeat analyses. I am only using 12 sec peak count times for those MAN fits though, and my wavescan was 40sec/pt so would have thought I may have still seen it. I guess I should repeat it with 80sec just to make doubly sure!
Interesting, yes I played around cranking it to XX as well but didn't see anything there. But it still has to be Ti doesn't it given we see it on the Ti metal scan?
A Ti emission line seems possible. But I looked in a Penepma 40 hour simulation and I see no Ti lines near 675 eV. Can't be oxygen since the mystery peak got larger in Ti metal.
Just to show how tiny this mystery peak is, here a scan of fluor-phlogopite and TiO2 on TAP:
(https://smf.probesoftware.com/gallery/395_15_09_17_6_31_03.png)
I figured I will post my MAN question under this thread. I've been doing some extensive MANing recently and I thought I would take a more systematic approach to see how each of my crystals and spectrometers respond. I haven't gotten around the the LDE crystals yet, however. The PET and LiF crystals I have perform beautifully and make a fairly straight line across the standards I have been using. My issue is with my TAP crystal. They all are showing some very non-linear behaviour. I have attached a file to show what I mean. I am a bit stumped to explain what's happening. Any suggestions or thoughts would be really appreciated!
Quote from: DavidAdams on October 04, 2017, 10:48:13 AM
I figured I will post my MAN question under this thread. I've been doing some extensive MANing recently and I thought I would take a more systematic approach to see how each of my crystals and spectrometers respond. I haven't gotten around the the LDE crystals yet, however. The PET and LiF crystals I have perform beautifully and make a fairly straight line across the standards I have been using. My issue is with my TAP crystal. They all are showing some very non-linear behaviour. I have attached a file to show what I mean. I am a bit stumped to explain what's happening. Any suggestions or thoughts would be really appreciated!
Hi Dave,
This is an entirely appropriate topic to ask these questions. The emission lines on the TAP crystal are lower energy and hence more subject to absorption (and surface contamination).
If you go back a few pages you can find Julien Allaz discussing MAN using TAP crystals here:
http://smf.probesoftware.com/index.php?topic=4.msg5295#msg5295
And Ben Buse discussing F Ka on TAP versus LDE1 using MAN here:
http://smf.probesoftware.com/index.php?topic=4.msg6230#msg6230
So *without* a blank correction the accuracy of the MAN method in silicates and oxides is limited to about 100 to 200 PPM. The accuracy will be less in higher Z materials due to the larger background correction.
But remember, the MAN correction can never overestimate your background correction, it can only underestimate it, that is if you have a subtle interference (or previously unsuspected contamination) in your standards used for the MAN calibration).
By the way I just run some trace elements in quartz using MAN (20 keV, 200 nA and 450 seconds count time) and here are the calculated detection limits for 5 points on my quartz standard (1.4 PPM Ti, 6 PPM Fe, 15 PPM Al and 0.03 PPM K from ICP-MS):
Un 7 std 14 as unk
TakeOff = 40.0 KiloVolt = 20.0 Beam Current = 200. Beam Size = 20
(Magnification (analytical) = 24000), Beam Mode = Analog Spot
(Magnification (default) = 600, Magnification (imaging) = 616)
Image Shift (X,Y): .00, .00
Number of Data Lines: 5 Number of 'Good' Data Lines: 5
First/Last Date-Time: 10/04/2017 01:02:50 AM to 10/04/2017 01:40:49 AM
WARNING- No MAN Background Count Data Calculated for ti ka
WARNING- Using Blank Trace Correction
WARNING- Using Alternating On and Off Peak Acquisition
WARNING- Using Aggregate Intensities for Duplicate Elements
Average Total Oxygen: 53.257 Average Total Weight%: 100.000
Average Calculated Oxygen: 53.257 Average Atomic Number: 10.805
Average Excess Oxygen: .000 Average Atomic Weight: 20.029
Average ZAF Iteration: 1.00 Average Quant Iterate: 4.00
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Element Si is Calculated by Difference from 100%
Un 7 std 14 as unk, Results in Elemental Weight Percents
ELEM: Ti Fe Al Ti K Si O
TYPE: ANAL ANAL ANAL ANAL ANAL DIFF CALC
BGDS: MAN MAN MAN MAN MAN
TIME: 450.00 450.00 450.00 .00 450.00 --- ---
BEAM: 200.37 200.37 200.37 .00 200.37 --- ---
AGGR: 2 --- ---
ELEM: Ti Fe Al Ti K Si O SUM
XRAY: (ka) (ka) (ka) (ka) (ka) () ()
98 .00016 .00043 .00180 .00000 -.00015 46.7411 53.2567 100.000
99 -.00005 .00080 .00198 .00000 .00004 46.7408 53.2564 100.000
100 .00013 .00081 .00193 .00000 .00025 46.7406 53.2563 100.000
101 .00021 .00078 .00129 .00000 -.00022 46.7413 53.2566100.0000
102 .00021 .00018 .00112 .00000 .00006 46.7417 53.2567 100.000
AVER: .00013 .00060 .00162 .00000 .00000 46.741 53.257 100.000
SDEV: .00011 .00028 .00039 .00000 .00018 .000 .000 .00000
SERR: .00005 .00013 .00018 .00000 .00008 .00020 .00007
%RSD: 79.9429 47.4139 24.1568 .0000 -8046.5 .00096 .00031
STDS: 22 395 374 0 374 --- ---
STKF: .5616 .6862 .0628 .0000 .1102 --- ---
STCT: 71054.0 32507.0 3454.7 .0 3953.0 --- ---
UNKF: .0000 .0000 .0000 .0000 .0000 --- ---
UNCT: .1 .2 .7 .0 .0 --- ---
UNBG: 89.4 34.1 34.6 .0 15.9 --- ---
ZCOR: 1.1969 1.1746 1.3479 .0000 1.2098 --- ---
KRAW: .00000 .00001 .00019 .00000 .00000 --- ---
PKBG: 1.00160 1.00712 1.01917 .00000 .99996 --- ---
INT%: ---- ---- ---- ---- ---- --- ---
BLNK#: 7 7 7 0 7 --- ---
BLNKL: .000140 .000600 .001500 0 .000000 --- ---
BLNKV: -.00181 -.00314 -.00262 0 .001041 --- ---
Detection limit at 99 % Confidence in Elemental Weight Percent (Single Line):
ELEM: Ti Fe Al Ti K
98 .00022 .00053 .00053 .00000 .00049
99 .00033 .00053 .00053 .00000 .00049
100 .00033 .00053 .00053 .00000 .00049
101 .00033 .00053 .00053 .00000 .00049
102 .00033 .00053 .00053 .00000 .00049
AVER: .00030 .00053 .00053 .00000 .00049
SDEV: .00005 .00000 .00000 .00000 .00000
SERR: .00002 .00000 .00000 .00000 .00000
Detection Limit (t-test) in Elemental Weight Percent (Average of Sample):
ELEM: Ti Fe Al Ti K
60ci .00005 .00015 .00022 --- .00011
80ci .00009 .00024 .00035 --- .00017
90ci .00012 .00034 .00049 --- .00024
95ci .00016 .00044 .00064 --- .00032
99ci .00026 .00073 .00106 --- .00052
Note that Ti is acquired on two spectrometers using the aggregate method, but it bests my previous record of 2-3 PPM using off-peak measurements on all *five* spectrometers for Ti. That is a 2.6 PPM t-test detection limit on Ti isn't too bad, using MAN on only two spectrometers!
What I think you are seeing in your TAP MAN plots (going up to Z = 90?), are very small spectral interferences (or contamination in some cases). Remember, those high order Bragg reflections are ubiquitous on TAP crystals...
The fact that they show some beautiful "progressions" with Z, tells me these are spectra interferences.
Here's what I tell my students: because background is *by definition* the lowest thing we can measure, any points that plot above the trend are either interference or contamination (or a little of both). Therefore, you can only remove those standards that plot above the trend in the MAN calibration curve.
Because the MAN intensities are corrected for absorption, there should be no sample absorption edges, so the lowest points should represent the actual background.
john
Hey, at least one can only have interferences on the on-peak intensities when using MAN background methods!
As opposed to the off-peak method which can have interferences both on the peak and also on the off-peak positions!
By the way, in the above run I only had Al ka on TAP, and while one could wish for more intermediate points around Z = 14 to 18, the fit is pretty smooth:
(https://smf.probesoftware.com/gallery/395_04_10_17_1_19_59.png)
Unfortunately my TiO2 has about 100 PPM of Al so it cannot be used.
john
Quote from: Owen Neill on October 04, 2017, 03:04:10 PM
Quote from: John Donovan on October 04, 2017, 01:22:30 PM
Unfortunately my TiO2 has about 100 PPM of Al so it cannot be used.
john
If you have an Al-free piece of V2O5, that's at about clocks in at Zbar ~ 16.4, or one of the synthetic Cl-apatites (~14.5).
Is that 100ppm real, or is that the Ti Ka III? Even in diff mode with a tight-ish window, I usually ended up excluding Ti-bearing standards from Al MAN curves.
Hi Owen,
The Al in TiO2 could certainly could be an interference from Ti Ka III, but the note in my standard database says that the 110 PPM Al is an "interference corrected" value... but that measurement was performed over 25 years ago so it should probably be revisited!
My V2O3 is from Purdue University:
Harrison, et al. 1980, Mat. Res. Bull., v. 15, pp. 571-580
It's behind a paywall so I can't read it and see how much Al might be present. I have no mention of Al in my standard database for this material.
john
QuoteA question by John Fournelle was particularly interesting and I had some additional thoughts on it. His question was: you said that background is generally the lowest thing we can measure, does the MAN correction handle situations where there are "holes" in the continuum?
Actually I wasn't referring to a "hole in the background" explicitly, rather to a "low spot" in the monazite bkg wavescan you showed, where the modeled background was higher than that low spot....I figured there must be some reason for the low spot, which could perhaps be a hole or perhaps not, but something else which might have another physical explanation.
Quote from: JohnF on October 25, 2017, 02:51:19 PM
Actually I wasn't referring to a "hole in the background" explicitly, rather to a "low spot" in the monazite bkg wavescan you showed, where the modeled background was higher than that low spot....I figured there must be some reason for the low spot, which could perhaps be a hole or perhaps not, but something else which might have another physical explanation.
OK, that is probably the Ar absorption edge from the detector (unlike the hole near the Au La from secondary Bragg diffraction). This paper by Jercinovic does discuss the issue of absorption edges creating "holes" in the continuum (see fig 23 for example):
http://www.geology.wisc.edu/~johnf/g777/AmMin/Jercinovic_2005.pdf
Of course this is the reason (traditional off-peaks or multi-point bgds), we generally don't want to interpolate off-peak measurements across an absorption edge. Wow, absorption edges from the sample, absorption edges from the Bragg crystal and absorption edges also from the detector. It's a jungle out there!
The interesting thing to me was that if the "hole" in the background is due to secondary diffraction from the Bragg crystal (or the Ar absorption edge from the detector), it won't affect the MAN method, but holes in the background due to an absorption edge in the sample could.
Though now that I think about it more, I am going to bet that the continuum absorption correction in the MAN background correction will take care of these sample absorption edges automatically! I mean that's what an absorption correction is for, right? But I wouldn't try the MAN bgd correction for monazite because it would be too difficult to obtain a suitable blank for checking accuracy. But assuming one can find a suitable blank, the MAN method might deal with all three types of absorption edges automatically!
I can't wait to get back in the lab and try measuring Au La in pyrite using MAN. I've never tried it, but my pure pyrite standard will make a great blank so it's worth a try...
Last month Ben Wade posted this interesting observation of a mystery emission line near F Ka in TiO2:
http://smf.probesoftware.com/index.php?topic=4.msg6305#msg6305
Here is a plot of fluor-phlogopite and TiO2 normalized intensity. I wanted to see if I could say whether the mystery line was a first order emission line or not:
(https://smf.probesoftware.com/gallery/395_31_10_17_6_39_17.png)
Just eyeballing it I'd say it looks about as wide as the F Ka emission, so yes, I think it is a first order line, but next I'll try some really high precision wavescans.
john
I have a question about the shape of the MAN background calibration curve. Sometimes when one plots up a large range of average Z, the trends show a positive curvature where the continuum intensities decrease with increasing Z as seen here:
http://smf.probesoftware.com/index.php?topic=4.msg5136#msg5136
For light elements or other low energy emission lines this could be due to increasing absorption in higher Z matrices, but the MAN absorption correction should deal with that I would think. So what else could it be? Obviously there is more backscatter at high Z, so there are fewer electrons staying in the matrix and hence less continuum x-ray generation. Also higher Z elements tend to produce less intensity for a given emission line since there are so many other probabilities for absorption and fluorescence (and emission).
From that same zircon run above here is the MAN curve for Hf Ma (a relatively low energy emission line) with the continuum absorption correction applied:
(https://smf.probesoftware.com/gallery/395_20_11_17_2_24_17.png)
and here is the same data without the continuum absorption correction applied:
(https://smf.probesoftware.com/gallery/395_20_11_17_2_25_07.png)
But the difference in curvature is slight. We need a suite of low energy x-ray emission lines measured over a large range of average Z to see better what is going on with continuum emission.
Quote from: Probeman on October 31, 2017, 06:43:32 PM
Last month Ben Wade posted this interesting observation of a mystery emission line near F Ka in TiO2:
http://smf.probesoftware.com/index.php?topic=4.msg6305#msg6305
Here is a plot of fluor-phlogopite and TiO2 normalized intensity. I wanted to see if I could say whether the mystery line was a first order emission line or not:
(https://smf.probesoftware.com/gallery/395_31_10_17_6_39_17.png)
Just eyeballing it I'd say it looks about as wide as the F Ka emission, so yes, I think it is a first order line, but next I'll try some really high precision wavescans.
john
Remember we noticed that we were seeing a very weak peak (possibly Ti) interfering with F Ka, but only for TAP crystals? The above plot scan is from my SX50 which just has normal sized TAP crystals (but using 60 sec per point), so I thought I would try again on my SX100 using the LTAP crystal and double the counting time expecting to see some even nicer looking peaks (we used 15 keV and 50 nA for all scans).
My first attempt surprised my students and I because there was no peak there! Here is using a LTAP crystals and 120 sec per point for TiO2 and Ti metal:
(https://smf.probesoftware.com/gallery/395_28_11_17_4_14_03.png)
So then I said, OK let's try 300 sec per point, and we got this:
(https://smf.probesoftware.com/gallery/395_28_11_17_4_14_19.png)
Pretty disappointing. This tells me that this peak is spectrometer/crystal dependent but still related to Ti content. I would guess that some cracks in the Bragg crystal are causing a secondary diffraction from some Ti emission and that is what we are seeing.
Here is a summary of Ti, TiO2, SrTiO3 and FeS2 with fluor-phlogopite as a F ka peak reference:
(https://smf.probesoftware.com/gallery/395_28_11_17_4_14_35.png)
I expect that my old Sx50 has a more cracked TAP and that is why this mystery peak artifact is more visible even at much shorter counting times.
I don't know what else to say...
john
Hi John
That is interesting. I guess that means both my TAP and LTAP are cracked or have defects then, much more so than your LTAP, as I see the mystery peak quite large at relatively on both. I have another TAP on sp2 I haven't checked but chances are its on that as well. Going by Owen's poor LTAP it looks like it could be quite prevalent. Would TAP xtals be more susceptible to internal stresses/damage over time than other crystals with different d-spacing? I couldn't imagine why really. Perhaps its on all xtals to some extent.
cheers
Quote from: BenjaminWade on November 28, 2017, 05:36:48 PM
Hi John
That is interesting. I guess that means both my TAP and LTAP are cracked or have defects then, much more so than your LTAP, as I see the mystery peak quite large at relatively on both. I have another TAP on sp2 I haven't checked but chances are its on that as well. Going by Owen's poor LTAP it looks like it could be quite prevalent. Would TAP xtals be more susceptible to internal stresses/damage over time than other crystals with different d-spacing? I couldn't imagine why really. Perhaps its on all xtals to some extent.
cheers
Hi Ben,
I really have no idea. If this peak is indeed merely a diffraction artifact, then the defects in the Bragg crystal might not even be visible to the eye.
john
Sorry for bringing up an old post, but I can confirm that this artifact is also visible on all our TAP crystals on SX100 and SXFiveFE. So it is rather not the mere artifact, but some systematic artifact. It reminds me a bit terrible systematic artifacts on all of our LPET's, which I guess are X-ray reflection from backside of diffracting crystal.