[Ifeffit] Preparation help with fly ash sample with diluted Tl
"Dr. Dariusz A. Zając"
kicaj at ifj.edu.pl
Fri Sep 30 01:32:38 CDT 2011
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"
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...
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.
> 2011/9/29 "Dr. Dariusz A. Zając"<kicaj at 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...
>> 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,
>>> On Thu, Sep 29, 2011 at 9:39 AM, Mengling Yi Stuckman
>>> <stuckman.12 at osu.edu> wrote:
>>>> Dear Ifeffit Community,
>>>> I am currently working on project "Evaluating Speciation of Thallium in
>>>> 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
>>>> 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
>>>> I understand that I should use Hephaestus, but I don't know how to do
>>>> 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
>>>> Any input would be highly appreciated,
>>>> Ifeffit mailing list
>>>> Ifeffit at millenia.cars.aps.anl.gov
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