[Ifeffit] how to use the data in the XAN library to estimate the transmission of an x-ray filter

pereira ninorpereira at gmail.com
Tue Apr 12 21:08:13 CDT 2016

Hi All,

new to this list and to the field, so please be patient and kind
and helpful in any response you may have. So far everyone I've
reached on this topic has been extraordinary good. I still have to
learn the lore though.

I'd like to compute the x-ray transmission as function of the x-ray
energy, for a particular mass per unit area of a substance, say Zn.
In the XAS data base I find Zn foil at room temperature, recently measured
and even more recently put into the data base just in time for
my purpose. Thank you!  The question is:  is there a ready-made program
to use those data? I see that your community has a whole slew of
programs that do the opposite, go from the attenuation and/or fluorescence
measured on a beam line to the attenuation coefficient, apparently without
having to know the mass per unit area of the filter. I see Demeter,
Athena, Larch, and various others but they all seem to go the wrong
way for (and much further than) what I need.

Instead, I'd like to pick up the data you guys measured on the synchrotron,
and convert those into the X-ray transmission of a filter for which I select
the mass per unit area.

In trying to figure out how to do this I look at the graphs in the database,
and the numbers behind Zn foil.xdi.

The graph on the top left side gives the "Raw XAFS" (y, say) as function 
of energy.
I interpret that as y = - ln (itrans/i0), where i0 and itrans are in    
  Zn foil.xdi
as the intensity of the incoming x-ray beam, and the beam behind the
particular filter. Far from the edge, at 9600 eV, I see i0=93769.049842
and itrans=56429.849906, so that y=0.508. I can't tell from the graph 
whether this
is indeed the case, so I go to the NIST tables. They give 35.05 cm^2/g 
on the
low side of the edge. Then, the mass per unit area of this particular foil
must have been 14.5 mg/cm^2.

At 10000 eV the same thing gives y=3.603. This is pretty close to what I
see in the graph, so I'm tempted to think that guessing "Raw XAFS"= 
However, for (mu/rho) NIST gives 233.1 cm^2/g, so I get for the foil's mass
per unit area 16 mg/cm^2. Not quite right.

Any comments on what I might have done wrong?

It seems to me that by measuring the transmission of a particular filter on
some X-ray source we might have available would then in effect measure
the mass per unit area, so that this can be taken into account by simply
exponentiating itrans/i0 with the right exponent ( = multiplying the
logs with the right factor).

Is something like this already implemented in one of your programs? If so,
which one?

Thank you,


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