[NewCandle] Nick's new pics

[John Winterflood]

Hi Nick, all,

Nick Reiter wrote:
> Good morning, John and all,
>
> Thank you for pointing out some aspects I will surely
> check into.
>
> The software I use in the EDS has the feature of being
> able to show the different excitation lines for the
> bands such as Kalpha, Lalpha, Lbeta.  Unless the
> double excitation of the Al is an artifact that is
> apart from the known excitation spectra, then it
> seemed pretty pristine to me.
>   
I am not sure quite what you mean by this last sentence.  But if you 
take a careful look at plots 3 and 5 where you have a particularly 
strong "Ag" peak, you might notice a cyan colored outline traced over 
the top.  My guess is that this cyan trace is the instrument telling you 
what an Ag peak should look like if it was real - ie in accompaniment 
with the strong (100%) peak at 2984, there should *always* be a (56%) 
smaller peak beside it at 3151.  Your high peaks at ~2984 do not have 
this validating neighboring peak => therefore I think they are not Ag!
> I run the EDS at 30 kV typically, sacrificing delicate
> surface analysis for a full look at heavier species -
> in my "day job" I typically have to look for Cd, Te,
> Sn, Mo.
>   
Ok, so if you operate at 30kv on Ag you should be able to see a pair of 
peaks near 22kev and a feeble one near 25kev.  These would be well worth 
checking for.
> I guess I have a couple of counterpoints to yours:
>
> 1.  A scan taken of the same foil in a control or
> un-processed state - a witness piece - at similar mags
> and same kV does not show the presumed Ag peak in
> question, even with the vertical scale stretched out,
> as I did on some shots showing the Ag.
>   
Under very similar operating conditions, I can not think of any reason 
why these double energy (they are called "pile-up") peaks would not be 
present.  But if the count rate or beam current (for instance) is 
reduced then it is quite possible that the peak may disappear below the 
background level.

Also it is possible that the software can (and should!) make allowance 
for these peaks by noting the pulse length and arrival rate and 
subtracting an appropriately estimated number of pulses from the 
spectrum in regions and at twice the energy of any main peaks present.  
Maybe this software doesn't do such a good job of removing these pile-up 
peaks when the main peaks are so high that they are strongly clipped?  
(I am just guessing).

By the way, another trap to watch for is the so-called "escape" peaks 
which are always present ~1.75kev below main peaks (I seem to recall 
being caught by one of them before!).  I don't think there are any 
obvious ones present in your spectra however.
> 2.  The Yttrium peak, also quite significant IMO, is
> as well something that appears to be genuinely related
> to the processed material in question, not an artifact
> of the process.  I attempted to scrutinize it to the
> same dgree as the Ag, by using the different spectral
> lines of neighboring elements to look for overlay,
> etc.
>   
I'd like to see what phosphorus (2014ev) peak overlay would look like on 
this supposed Yttrium (1922ev) one.  While I can't see much more reason 
for phosphorus impurity (or transmutation!) over and above Yttrium, it 
seems that there is scarcely any peak at 15kev - which Yttrium should 
have.  Phosphorous on the other hand has no high energy peaks and may 
have a more prosaic explanation (such as sodium or calcium phosphate in 
your table salt?).  Mind you I really don't recall the typical relative 
magnitudes of high energy compared to low energy peaks.

Kindest regards.

J.