Author Topic: Questions about MAN background use  (Read 14123 times)

BenjaminWade

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Re: Questions about MAN background use
« Reply #90 on: September 13, 2017, 06:45:28 pm »
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

Malcolm Roberts

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Re: Questions about MAN background use
« Reply #91 on: September 13, 2017, 07:09:47 pm »
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.

BenjaminWade

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Re: Questions about MAN background use
« Reply #92 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.

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Malcolm Roberts

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Re: Questions about MAN background use
« Reply #93 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 Roberts

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Re: Questions about MAN background use
« Reply #94 on: September 13, 2017, 08:24:42 pm »
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??

Probeman

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Re: Questions about MAN background use
« Reply #95 on: September 13, 2017, 08:34:36 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?
The only stupid question is the one not asked!

Malcolm Roberts

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Re: Questions about MAN background use
« Reply #96 on: September 13, 2017, 08:40:24 pm »
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.

Probeman

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Re: Questions about MAN background use
« Reply #97 on: September 13, 2017, 08:41:34 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
« Last Edit: September 13, 2017, 08:45:13 pm by Probeman »
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Probeman

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Re: Questions about MAN background use
« Reply #98 on: September 13, 2017, 08:43:59 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
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Malcolm Roberts

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Re: Questions about MAN background use
« Reply #99 on: September 13, 2017, 11:20:35 pm »
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!!

BenjaminWade

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Re: Questions about MAN background use
« Reply #100 on: September 13, 2017, 11:56:59 pm »
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...

Probeman

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Re: Questions about MAN background use
« Reply #101 on: September 14, 2017, 08:44:22 am »
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
« Last Edit: September 14, 2017, 09:34:43 am by Probeman »
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BenjaminWade

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Re: Questions about MAN background use
« Reply #102 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

Probeman

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Re: Questions about MAN background use
« Reply #103 on: September 14, 2017, 05:54:08 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:



So the mystery emission line does not reveal its true identity easily!  Who will solve this conundrum?    :D
john
« Last Edit: September 14, 2017, 06:43:14 pm by Probeman »
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BenjaminWade

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Re: Questions about MAN background use
« Reply #104 on: September 14, 2017, 07:06:43 pm »
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?