Re: [Ifeffit] Ifeffit Digest, Vol 158, Issue 3

Hi Bruce, Thanks for your help, it's really appreciated. I was trying to keep it simple but it seems I'm just messing around. What I am trying to do is to perform a new developed self-absorption correction using collected fluorescence absorption coefficient data on a CuSO4 (pentahydrate) capillar (cylinder) and spherical sample with Cu as absorber, having different values of molarity and penetration depth. The correction expression requires these measured quantity: μX(E) : the absorption coefficient due to a given core excitation of the absorbing atom - I used the background function for this ( bkg(E)) μo = μ(E) : photoelectric total linear absorption coefficient of the sample at incident energy E - I used the xmu(E) for this μh = μ(E) :photoelectric total linear absorption coefficient of the sample at fluorescence emission Ef - I used the xmu(Ef) with Ef the K absorption edge of Cu ( 8.9789 eV) χ: and here I used the chi(E) values of the exported ascii .xmu file Hope it's clear now. Matteo 2016-04-02 19:00 GMT+02:00 :

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1. Re: Ifeffit Digest, Vol 158, Issue 1 (Matt Newville)

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Message: 1 Date: Fri, 1 Apr 2016 15:56:29 -0500 From: Matt Newville To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Ifeffit Digest, Vol 158, Issue 1 Message-ID: Content-Type: text/plain; charset="utf-8"

Matteo,

On Fri, Apr 1, 2016 at 8:35 AM, Matteo Busi wrote:

...

Hi Bruce, Now this is clear. In my case the correction I have to perform requires these measured/evaluated parameters: chi, mu (not sure if it's better to work with normmu here) and the background function. Is it physically meaningless to have the mu(k) and bkg(k) data? If that is not the case I would like to have these two columns exported in the ascii chi(k) file. So then I can perform the correction and re-import the new corrected chi(k) and make comparison with the uncorrected.

Kind regards, Matteo

It would certainly help (and by that I mean "help you get the answers you're looking for") if you gave us more details about what you're trying to do rather than ask for how to what you think you want to do.

Just to be clear: Converting from E to k does not involve a Fourier transform, just k = sqrt((2m*e/hbar**2)*(E-E0))

for k in Ang^-1 and E in eV, that's k ~= sqrt(0.262468*(E-E0))

I'm not sure what you're trying, but I would image you want to use normalized mu(E) or at least pre-edge subtracted mu(E). That is, what we call mu(E) is typically really -ln(I/I0) where I and I0 are not the actual intensities before and after the sample, but counts or counts per time in some detector that samples the flux. These values include more or less arbitrary scale factors (amplifier gains, etc) included. That means that (unless you very careful) mu(E) does not have meaningful units, certainly not cm^-1 or cm^2/gram.

Normalized mu(E) doesn't have such units either, but it's an easier place to start.

--Matt