# [Ifeffit] Ifeffit Digest, Vol 158, Issue 1

Matt Newville newville at cars.uchicago.edu
Fri Apr 1 15:56:29 CDT 2016

```Matteo,

On Fri, Apr 1, 2016 at 8:35 AM, Matteo Busi <basebush at gmail.com> 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
>
>
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
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