Using Probe for EPMA software in "demonstration mode" to teach EPMA

[Probeman]

This year and last year my lab manager Julie Chouinard, has been utilizing the Probe for EPMA software in "demonstration mode" to teach students how to run the electron microprobe.  She's had the students install the software on their laptops so they can practice setting up runs using the "demo" mode that is enabled by default when installing the software on a new computer.

Her main goal was to reduce time spent actually on the instrument for training new users, but recently, several students have told me that working with the software on their laptops has been a big help in learning the technique in general.  I originally developed the demo mode just for my own testing, but I think it could be a good tool for teaching as well. What do you all think?

If this is true maybe it makes sense to make the "demo" mode even more realistic.  Right now one can acquire standards in "demo" mode and the software will automatically generate the correct intensities using the physics models in PFE. This allows students to "run" both primary and secondary standards for checking "accuracy" (by utilizing different matrix corrections) as described here:

http://probesoftware.com/smf/index.php?topic=508.msg2779#msg2779

On a related topic it should be mentioned that setting these parameters in the probewin.ini file

EDSSpectraInterfacePresent=1    ; non-zero EDS spectrum interface feature available (Thermo, Bruker, etc)
EDSSpectraInterfaceType=0    ; 0 = Demo, 1 = Edax, 2 = Bruker, 3 = Oxford, 4 = Unused, 5 = Thermo NSS, 6 = JEOL
EDSSpectraNetIntensityInterfaceType=0    ; 0 = Demo, 1 = Edax, 2 = Bruker, 3 = Oxford, 4 = Unused, 5 = Thermo NSS, 6 = JEOL

Allows one to also automatically acquire EDS spectra based on the actual composition, e.g., standards, using the Penepma Monte Carlo software that is automatically installed by the CalcZAF installer, as seen here:

http://probesoftware.com/smf/index.php?topic=481.msg5267#msg5267

Unfortunately I still don't have a "demo" code for stripping the background to get net intensities for EDS elements, yet...  but it occurs to me that if using PFE in "demo" mode is an effective method for teaching EPMA to students and/or new users, I wonder if making the PFE "demo" even more realistic would be a good idea...

For example, currently the wavecan acquisition in "demo" mode just shows a single large analytical peak (based on the actual element concentration!), but no other secondary peaks, or peaks from other elements.  But I realized that if I utilize the code that I wrote to generate the Monte Carlo EDS spectra, and convolve it as higher resolution for WDS, all the peaks would be there.  I have to think about how I would add higher order Bragg reflections to this Monte-Carlo spectrum, but even just the first order lines would be more realistic for teaching.

What do you all think of this?  Would using a more realistic "demo" mode in PFE be useful for teaching students and/or new users?
john

[John Donovan]

I just thought of one small "fly in the ointment" for utilizing Penepma Monte Carlo calculations for accurate "demo" mode wavescans. And that is that while this method works fine for EDS demo mode acquisitions (because as the calculation statistics improve, the full EDS spectrum is updated during the acquisition), but in the case of WDS scans, the Monte Carlo calculation will be proceeding as the WDS scan proceeds, meaning that the beginning portion of the scan will have considerably worse statistics than the later WDS points, since WDS points are acquired serially...  I have to think more about this.

Maybe I should simply pre-calculate 100 pure element spectra using Penepma and then simply synthesize them for the material in question...?   With some correction for matrix effects.  A bit brute force, but at least no further Monte Carlo calculations are required. Obviously, the beam energy is a factor that needs to be dealt with, but we could start with 15 keV and go from there...

[Probeman]

Maybe I should simply pre-calculate 100 pure element spectra using Penepma and then simply synthesize them for the material in question...?   With some correction for matrix effects.  A bit brute force, but at least no further Monte Carlo calculations are required. Obviously, the beam energy is a factor that needs to be dealt with, but we could start with 15 keV and go from there...

I believe that "synthesizing" demonstration wavescans in real time by utilizing 100 pure elements spectra pre-generated by Penepma will be the way to go forward on this. At least it will be a fun project for the holidays... so with that in mind, I've started Monte Carlo calculations of all pure elements in Penepma running one of my servers to an arbitrary level of precision (~40 hours per element).

I'll have to convolve the Penepma spectral resolution as a function of Bragg crystal 2d (and possibly spectrometer position) and also figure a way to generate higher order reflections as well... should be interesting!
john

[John Donovan]

The latest version of PfE, now displays realistic PHA scans in *demo mode* both for traditional PHA scans, and Cameca MCA PHA scans as seen here:

[Probeman]

Can anyone tell me roughly what the FWHM in eV is for the basic Bragg crystal types? The book I think it might be in, is at my UofO office and I'm working at Probe Software today!

I realize WDS spectral resolution varies over the spectrometer range, for example, the lower spectrometer angles yield worse spectral resolution because the angle of diffraction is lower (more grazing) and therefore fewer crystal lattice layers are involved in the diffraction.  But I only need rough numbers...

So in eV, what are the rough spectral resolutiuon for these Bragg crystals in eV? Or any units for that matter!

LIF:
PET:
TAP:
PC0:
PC1 or LDE1:
etc.

Thanks,
john

[Anette von der Handt]

I am actually in the process of extracting this information from the many demo data that I got, so hopefully can provide you with some numbers. But what is the book that you are thinking of? I may have it at hand.

[Probeman]

I am actually in the process of extracting this information from the many demo data that I got, so hopefully can provide you with some numbers. But what is the book that you are thinking of? I may have it at hand.

Hi Anette,
It's a small, slim volume with an orange book sleeve. I think it was called something like "Principles of X-ray Spectrometery" or a variation on that.
john

[Anette von der Handt]

Hi John,
I only have a slim orange volume for "Electron Beam Analysis" and it does not list it. However I could pull the numbers from Virtual WDS. I picked one element at the high and the low range for each crystal type Let me know if you need any others one in particular.

TAP F: 0.0012
TAP Si: 0.0019

PET Si: 0.0012
PET Mn: 0.0023

LIF Ca: 0.0012
LIF Fe: 0.0013
LIF Br: 0.0021

LDE1 C: 0.0012
LDE1 F: 0.0018

LDE2 B: 0.0012
LDE2 N: 0.0016

I guess the unit is keV

Btw, even if you don't have Virtual WDS, you can get a trial version if you want to peruse it yourself.

Hope this helps for now.

Cheers,
Anette

[Probeman]

TAP F: 0.0012
TAP Si: 0.0019

PET Si: 0.0012
PET Mn: 0.0023

LIF Ca: 0.0012
LIF Fe: 0.0013
LIF Br: 0.0021

LDE1 C: 0.0012
LDE1 F: 0.0018

LDE2 B: 0.0012
LDE2 N: 0.0016

I guess the unit is keV

Hi Anette,
This can't be correct.  For example, I know that LIF has better resolution than TAP, but this table has them being all about the same.   And certainly the multi-layer diffractors are *much* lower resolution than even TAP.  Just think about F Ka on TAP vs. LDE1.

See Ti Ka scanned on LIF and PET attached below.  The LIF scan is clearly resolving at higher resolution. In fact if I plot them in keV units I see FWHM values around 27 eV for PET and 11 eV for LIF.
john

PS I guess I partially answered my own question!   But I'd be interested if anyone has actually measured these themselves for the other crystals, TAP, LDE/PC...

[Brian Joy]

See Ti Ka scanned on LIF and PET attached below.  The LIF scan is clearly resolving at higher resolution. In fact if I plot them in keV units I see FWHM values around 27 eV for PET and 11 eV for LIF.

When I guesstimate FWHM for Ti Ka1 measured using LiF with 550-micron detector slit (see plot below), I get ~3.7 eV (and ~5.0 eV for Ba La1).  I've also attached the original Excel file, which contains a molybdenite WDS/PET versus EDS example as well.  I haven't compared with results from large-area and "high intensity" crystals.

[Probeman]

See Ti Ka scanned on LIF and PET attached below.  The LIF scan is clearly resolving at higher resolution. In fact if I plot them in keV units I see FWHM values around 27 eV for PET and 11 eV for LIF.

When I guesstimate FWHM for Ti Ka1 measured using LiF with 550-micron detector slit (see plot below), I get ~3.7 eV (and ~5.0 eV for Ba La1).  I've also attached the original Excel file, which contains a molybdenite WDS/PET versus EDS example as well.  I haven't compared with results from large-area and "high intensity" crystals.

That is much closer to what I would expect. In fact my Ti Ka scan on LIF shows both the Ka1 and Ka2, so my FWHM guess is wider than it should be.

And if I plot it in keV space and measure more carefully above the Ka1 Ka2 split, I get about 5 eV for the Ti ka FWHM which is closer to your guess:



john

[Anette von der Handt]

When I guesstimate FWHM for Ti Ka1 measured using LiF with 550-micron detector slit (see plot below), I get ~3.7 eV (and ~5.0 eV for Ba La1).

Very good guesstimate. I get 3.2 eV for Ti ka and 4.8 eV for Ba La on Brian's data (thanks for providing the raw data).

[Anette von der Handt]

I am slowly making my way through my wavescans. I hope I can give a proper list soon.

[Probeman]

Anette and Brian,
I am doing something wrong or there is something very different between JEOL and Cameca spectrometers (the Cameca spectrometers have just a fixed slit which makes it easier to test for one thing!). 

I simply went into the PFE Plot! window, selected the wavescan and then clicked the kilovolts option for the x-axis and for PET I get this:



Note that the Si Ka satellite lines are well resolved away from the main Si Ka peak! Using the mouse cursor the display indicates a FWHM of ~0.002 keV or ~2 eV.  If I now plot the same peak using TAP I get this:



Note that the Si Ka satellite lines on PET are now convolved *with* the Si ka main peak!  And the Si Kb line is now visible! 

Again using the mouse cursor data control I estimate the FWHM at 0.01 or ~ 10 eV.

Could the JEOL and Cameca spectrometers really have this much difference for PET and TAP?  Do you two have any scans of Si Ka like this?

Anette: please try the kilovolts option in the PFE Plot! window and see what you get.   I've attached the MDB file below if you want to play with my data in PFE.

This is very strange.
john

[Brian Joy]

Hi John,

Below is a comparison of scans across the Si Ka peak that I collected on "pure" Si using TAP and PETL crystals; I used the 550 and 500 micron detector slits, respectively.  I tend to leave the slits in the 500/550 micron position (tab lifted fully) over the long term because 1) I don't really like sticking the "screwdriver" into the spectrometers except for crystal alignments, 2) sometimes the tab doesn't lock securely into the desired position, and 3) this slit provides a good balance between resolution and count rate.  For Si Ka on PETL, I get FWHM = 2.34 eV, and, for Si Ka on TAP, I get FWHM = 6.78 eV.