Hi Matt,
I didn't know what kind of detector is on 5-BM-D beamline and what the
size of the beam is, so my answer was more general, and bases on my
experience from Hasylab. I have checked now: Canberra 13-element SSD and
15x5mm2 unfocused. So, I would follow your suggestion and start with
13-element detector. Making a pellet, I suppose, will help for "broad"
unfocused beam.
Unfortunately I have no comparable results for PFY and TFY detection,
but I have tried to measure fresco's pigments and it didnt work with
7-pixel Si(Li) Gresham but worked with PIPS diode.
There is one more idea, but I do not know if this sample is crystalline
or amorphous. In the first case maybe DAFS could help. I suppose it is
possible at 5-BM-D...
kicaj
W dniu 11-09-30 01:51, Matt Newville pisze:
Hi Dariusz,
Thanks, those are good suggestions. I was assuming that they'd use a
solid state (say 10+ element Ge) detector for concentrations at and
below 10 ppm. A large diode detector might work OK -- they can
often take higher total count rate at the expense of energy
discrimination. I'd be happy to be shown a comparison, but my guess
is that electronically removing the Fe and Compton scattering would be
worth the effort for these concentrations.
--Matt
2011/9/29 "Dr. Dariusz A. Zając"<ki...@ifj.edu.pl>:
Dear Matt,
this is very good introduction for fluorescence measurements on diluted
samples... Like a tutorial...
I just want to add small comments: as I understood the sample is an ash, so
maybe will be possible to condense it, e.g. press it into the pellet. If
there will be no possible to measure exafs (due to heavier elements), and is
needed to focus on xanes, than I suggest to use non-energy dispersive
detector, e.g. PIPS diode. It is very often more sensitive than regular
fluorescence detectors, and can take higher count-rate.
please correct me if I am wrong...
kicaj
W dniu 11-09-29 17:02, Matt Newville pisze:
Dear Mengling,
The basic issues are: will there be enough Tl fluorescence counts in
the detector, and will you be able to see a decent edge. From you
spreadsheet of concentrations, the elements that stand out are: Fe
and to a lesser extent Zn, and Pb.
The Fe and Zn will dominate the fluorescence getting to your detector.
This hurts sensitivity to Tl because the solid-state detectors can
handle a limited flux themselves (typically on the order of 100K Hz).
The high Fe concentration means the Fe Kalpha will dominate the
emission when you shine 12.7keV x-rays on the sample. The
simple-but-effective remedy is to put aluminum foil on the detector,
as aluminum will absorb Fe fluorescence (at 6.4keV) about 4x more than
the Tl fluorescence (at 10.3keV). You might need a few hundred
microns of aluminum foil, and may need to try a few different amounts
to cut down the Fe counts sufficiently.
The other issue is Pb. The Tl L3 edge is at 12.658keV. once you hit
the Pb L3 edge, at 13.1 keV, the Pb Lalpha fluorescence will dominate
the Tl Lalpha fluorescence -- these lines (10.3 and 10.5 keV,
respectively) are too close together to effectively filter
electronically. Even well below the Pb L3 edge, you'll start to see
some Pb Lalpha fluorescence. Since the Pb concentration might be 100x
the Tl concentration, that would be something to look for, but there's
not a lot that can be done about it. Anyway, that really only limits
the EXAFS, not so much the ability to get XANES. The Tl
concentrations are low, but I think that at a good APS BM line like
5-BM, getting Tl L3 XANES is just a matter of time.
Hope that helps,
--Matt
On Thu, Sep 29, 2011 at 9:39 AM, Mengling Yi Stuckman
<stuckman...@osu.edu> wrote:
Dear Ifeffit Community,
I am currently working on project "Evaluating Speciation of Thallium in
Coal
Fly Ash". The project was accepted by APS and we will conduct our
measurement on beamline 5-BM-D.
My fly ash sample has Tl concentration ranging from 0.5ppm to 13ppm. How
can
I know whether the sample can generate enough photon counts if using
fluorescence mode? what would be the appropriate sample preparation
procedure I should follow? Is there any interference I should pay
attention
to?
I understand that I should use Hephaestus, but I don't know how to do
that
if my sample contains lots of different oxides. I attached the elemental
composition in this email. Most metals should be in form of oxides, or
sulfates.
Any input would be highly appreciated,
Mengling
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