[Ifeffit] Problem with Hephaestus at Ca L-edges (Matthew Marcus)

[Bruce Ravel]

On 09/24/2015 01:43 PM, Matthew Marcus wrote:
> See the attached ppt for the demo.  I think this gives the whole
> repeat-by and interpretation.  Am I just missing something?  That would
> not be totally surprising.

The algorithms in Hephaestus are pretty dim-witted and tuned (such as 
they are) to getting the calculations more or less right in the hard 
X-rays.  I don't even try to do calculations in the soft x-ray range 
correctly.  For example, the edge step calculations do the calculation 
at something like +/-50, which is a very stupid choice for soft x-ray 
energies.  That should explain why L2:l3 ratio is 1.  Presumably also 
why the L1 step is negative!

See, e.g. 
https://github.com/bruceravel/demeter/blob/master/lib/Demeter/UI/Hephaestus/Formulas.pm#L274

You cannot trust anything Hephaestus has to say about edge jumps below 
3-ish keV.  Since the +/-50 is hard wired in, the jump ratios will be 
nonsense for any element for which the energy difference between the L2 
and L3 edges is less than 100 eV.

The Delta mu/rho numbers that you cite are interpolated from the Elam 
(usually) tables and should reliable to whatever extent you consider the 
table reliable.

B


-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
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