Dear All, Matteo It is difficult to do post facto, but if you have a well-defined solid, foil or crystal then mapping the thickness, measuring the mass and hence determining the mass per unit area, for the exact region illuminated by the beam, provides accurate units. Usually you will need to make a measurement of the average m/A from (i) total mass and (ii) total area, and then (iii) map the whole sample with X-ray tomography and (iv) the region illuminated by the X-ray beam.
We have a series of papers which explain more than one methodology for doing that within the XERT technique. If your sample is a solution it is a bit more tricky, and I would refer you to recent JSR and JPCC papers for our Hybrid technique. Both can work well but need a bit more care than a normal XAFS measurement. Best wishes Chris ------------------------------------------------------------ Christopher Chantler, Professor, FAIP Editor-in-Chief, Radiation Physics and Chemistry Chair, International IUCr Commission on XAFS President, International Radiation Physics Society School of Physics, University of Melbourne Parkville Victoria 3010 Australia +61-3-83445437 FAX +61-3-93474783 chant...@unimelb.edu.au chant...@me.com http://optics.ph.unimelb.edu.au/~chantler/xrayopt/xrayopt.html http://optics.ph.unimelb.edu.au/~chantler/home.html ________________________________________ From: Ifeffit [ifeffit-boun...@millenia.cars.aps.anl.gov] on behalf of ifeffit-requ...@millenia.cars.aps.anl.gov [ifeffit-requ...@millenia.cars.aps.anl.gov] Sent: Saturday, 14 May 2016 3:00 AM To: ifeffit@millenia.cars.aps.anl.gov Subject: Ifeffit Digest, Vol 159, Issue 3 Send Ifeffit mailing list submissions to ifeffit@millenia.cars.aps.anl.gov To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-requ...@millenia.cars.aps.anl.gov You can reach the person managing the list at ifeffit-ow...@millenia.cars.aps.anl.gov When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..." Today's Topics: 1. How to assign measure unit to XAFS data (Matteo Busi) 2. Re: How to assign measure unit to XAFS data (Alexey Boubnov) 3. Re: How to assign measure unit to XAFS data (Matt Newville) ---------------------------------------------------------------------- Message: 1 Date: Fri, 13 May 2016 02:11:39 +0200 From: Matteo Busi <baseb...@gmail.com> To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] How to assign measure unit to XAFS data Message-ID: <CAOyEiGg1N7wL-tnzPXFBCrUYQD=6=bvsrfndnee3zaceguf...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hi Bruce, Matt, and mailing list readers, I have one question regarding the XAFS data. I have collected absorption coefficient in fluorescence regime of a CuSO4 penta hydrate sample(however my question can be generalized to any compound). Through Athena I then obtained the x\mu(eV) spectra as well as \chi(k) and \chi(R). I am wondering how can I assign a unit to the x\mu values. I would like to have it in the cm^-1 or cm^2 kg^-3 unit so than I can match it with tabulated data for the Copper absorption coefficient and proceed with my studies. In case a treatment is needed for the normalized \mu , that would also suit my situation. My idea was to divide by the thickness of the sample but I don't find a reasonable justificiation for this. I really hope I made the question clear to any reader this time, and if that is not the case I apologyze in advance. Best Regards Matteo -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20160513/ce7b5ce8/attachment-0001.html> ------------------------------ Message: 2 Date: Fri, 13 May 2016 08:29:15 +0200 From: Alexey Boubnov <alexeyboub...@gmail.com> To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov> Subject: Re: [Ifeffit] How to assign measure unit to XAFS data Message-ID: <cajzpk0vrrq2ad-mxr2q4kdzorjdt_ceavropo3m57lyus_c...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Dear Matteo, ?x that you measured is dimensionless: x in the thickness (in cm) and ? the Absorption coeffiecient (per cm). Indeed, if you want to know the Absorption coefficient ? of your sample, you should divide ?x by x. All the best, Alexey 2016-05-13 2:11 GMT+02:00 Matteo Busi <baseb...@gmail.com>: > Hi Bruce, Matt, and mailing list readers, > > I have one question regarding the XAFS data. I have collected absorption > coefficient in fluorescence regime of a CuSO4 penta hydrate sample(however > my question can be generalized to any compound). > Through Athena I then obtained the x\mu(eV) spectra as well as \chi(k) and > \chi(R). I am wondering how can I assign a unit to the x\mu values. I would > like to have it in the cm^-1 or cm^2 kg^-3 unit so than I can match it with > tabulated data for the Copper absorption coefficient and proceed with my > studies. > > In case a treatment is needed for the normalized \mu , that would also > suit my situation. > > My idea was to divide by the thickness of the sample but I don't find a > reasonable justificiation for this. > > I really hope I made the question clear to any reader this time, and if > that is not the case I apologyze in advance. > > Best Regards > Matteo > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20160513/e09233a7/attachment-0001.html> ------------------------------ Message: 3 Date: Fri, 13 May 2016 07:13:08 -0500 From: Matt Newville <newvi...@cars.uchicago.edu> To: XAFS Analysis using Ifeffit <ifeffit@millenia.cars.aps.anl.gov> Subject: Re: [Ifeffit] How to assign measure unit to XAFS data Message-ID: <ca+7esbq84zpyx9dvp8jvm7ynzo0u31jfczz-_x43b21sm43...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hi Matteo, On Thu, May 12, 2016 at 7:11 PM, Matteo Busi <baseb...@gmail.com> wrote: > Hi Bruce, Matt, and mailing list readers, > > I have one question regarding the XAFS data. I have collected absorption > coefficient in fluorescence regime of a CuSO4 penta hydrate sample(however > my question can be generalized to any compound). > Through Athena I then obtained the x\mu(eV) spectra as well as \chi(k) and > \chi(R). I am wondering how can I assign a unit to the x\mu values. I would > like to have it in the cm^-1 or cm^2 kg^-3 unit so than I can match it with > tabulated data for the Copper absorption coefficient and proceed with my > studies. > The analysis tools treat "xmu" as a dimensionless value. To get values for the mu in cm^-1 or grm/cm^2, you'll have to convert the measured values used for XAFS analysis (say, readings from ion chambers) into actual X-ray intensities, and try to account for anything else in the beam path that will attenuate the X-rays. For measurements made in transmission, this can be done. In fact, for most transmission measurements, the *change* in -ln(I0 / I1) is usually a very good measure of the change in absorption of the sample, so that if the observed jump is a value of 2, the sample really did change its absorption by Delta_xmu = 2. But the absolute values for xmu are definitely not in meaningful units. Typically, the photo-current from the ion chamber or diode is converted to a voltage and then summed over some time period in a data acquisition system. You'd have to know the details of that system to convert the "I0" and "I1" numbers into actual beam intensities. For fluorescence measurements, the situation is worse. You'd need a very good measure of the solid angle of your detector, fluorescence efficiency, and the attenuation of the fluorescence getting from the sample to the detector. Depending on the detector type, you'd also need a good assessment of the backgrounds. It's probably not impossible, but I think it would not be easy unless that was the actual point of the experiment and you made many careful measurements of the detection system. If you're asking this question here, you'd didn't make those measurements. > > In case a treatment is needed for the normalized \mu , that would also > suit my situation. > > My idea was to divide by the thickness of the sample but I don't find a > reasonable justificiation for this. > If you're measuring in fluorescence, dividing by the thickness of the sample is not what you want. > > I really hope I made the question clear to any reader this time, and if > that is not the case I apologyze in advance. > > Cheers, --Matt -------------- next part -------------- An HTML attachment was scrubbed... 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