The downside of non-energy resolving detectors in this context is the huge background from elastic, as well as everything else. You would need to have exquisitely good normalization to get decent data after background subtraction on something that dilute. OTOH, Fred M. implies a good point about micro XAS which I'll make explicit: if the Tl is present as hotspots, then the local concentration is much higher than 13ppm, so you still might get something even though you can't throw as many photons at it as you could on a bulk line. Further, depending on how the Pb is distributed, you might even get lucky and avoid the Pb, if it's also present as independent big particles. There are some beamlines which have high-rate detectors. The one I know best, ALS 10.3.2, has a 7-element detector which can easily count up to 300k cts/sec total, which may be enough after Al-foil filtration. Other beamlines have up to 32 elements or even more. New detectors being developed will really blow past the count-rate barriers. An advantage of multiple-element detectors is if the sample is highly crystalline, you can get Bragg beams thrown at the detector at certain energies, causing peaks in your data. Often, these peaks will appear in only a subset of detector elements, so you can mask them off. Another possibility is a bent-Laue analyzer or other crystal optic. You'd have to have one made specifically for Tl, but it should work nicely. That energy range is a good one for these devices. mam On 9/29/2011 10:49 PM, fred.mosselmans@diamond.ac.uk wrote:

Dear Mengling,

As Caroline Peacock from Leeds has successfully done Tl L3 microXAFS on some samples on I18 at diamond, I Have a little experience.

She has a paper on the work currently in review.

As Matt says if you have Pb in the sample your data is limited to just under 350 eV (10 k). Micro EXAFS past 10 k is quite hard but feasible and the big advantage is your localised concs. are possibly (probably?) a lot higher than for the bulk. If the Tl was equally distributed at 13 ppm max then micro Xanes might work, XAFS wont – but i think that’s not likely. Thus with a local high concentration you might with time get 12 k XAFS from the Tl.

As for using a total yield detector the big advantage is that they are count rate unlimited so you don’t have to worry about count rate saturating your detector and can have it dead close to the sample to get the maximum Tl counts. Even with Al attenuation which will remove the Fe signal quicker than the Tl you are throwing away some Tl counts. Hence for XANES in particular it may be advantageous.

Cheers

Fred

Prof. J F W Mosselmans

Principal Beamline Scientist I18

Diamond Light Source

Diamond House

Harwell Campus

Didcot

Oxon

OX11 ODE

UK

T 00 44 1235 778568

M 00 44 7785510211

E fred.mosselmans@diamond.ac.uk

F 00 44 1235 778448

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