Hi Matt. Thanks for the hints, they are very useful. What would you suggest to use if not the bkg? Regarding the xmu(E) I have been using exactly the values exported through the .xmu ascii file. I have been reading though the Athena's user guide and I didn't find any hint about which unit I could assign to them. Anyway I would like to get them with the cm^-1 units which would suit with the correction expression I want to perform. How can this be done? My idea was to divide the xmu data by the penetration depth in the sample (i.e. the radius of the capillar sample). Is this correct? Can this be applied to the bkg data aswell? Moreover the data I have is not scanned through the Cu fluorescence energy you have mentioned (8046 eV). Would you recommend to use data from Chantler or Cromer-Liberman? And how can I merge it with my other measured data to make it unit meaningful? Thanks and regards, Matteo I report our previous conversation for reference:

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: ?X(E) : the absorption coefficient due to a given core excitation of the absorbing atom - I used the background function for this ( bkg(E))

Wouldn't using bkg(E) suppress the fine-structure you are trying to recover? Anyway what are the units, are you normalizing bkg(E) to something meaningful? I would suggest using data from Chantler or Cromer-Liberman here. Or perhaps match mu(E) or bkg(E) to these.

?o = ?(E) : photoelectric total linear absorption coefficient of the sample at incident energy E - I used the xmu(E) for this

Again, be mindful of what the units are.

?h = ?(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)

I am pretty sure that this is not what you want. You probably want mu(E) at the Cu fluorescence energy (8.046 keV). This can make a significant difference.