NAME

Xray::FluorescenceEXAFS - Corrections for fluorescence EXAFS data

DESCRIPTION

This provides class methods for computing corrections to fluorescence EXAFS data due to normalization, I0, and self-absorption effects. The corrections are computed from x-ray absorption coefficients provided by the Xray::Absorption package.

METHODS

Note that the values returned for all methods depend on the data resource used. See Xray::Absorption.

mcmaster

This is called mcmaster for historical reasons. It calculates the normalization correcion for a given element.

  $sigma_mm = Xray::FluorescenceEXAFS->mcmaster($element, $edge);

It takes the central atoms tag and the alphanumeric edge symbol as arguments and returns the normalization correction in units of Angstrom squared.

normalization and edgestep are aliases for this method.

i0

This calculates the correcion due to the I0 fill gases in a fluorescence experiment.

  $gases = {nitrogen=>$nitrogen, argon=>$argon, krypton=>$krypton};
  $sigma_i0 = Xray::FluorescenceEXAFS->i_zero($central, $edge, $gases);

It takes the central atoms tag, the alphanumeric edge symbol, and a reference to a hash containing the volume percentages of the three gases as arguments. It assumes that any remaining volume is filled with helium and it correctly accounts for the fact that nitrogen is a diatom. It returns the I0 correction in units of Angstrom squared.

i_zero and izero are aliases for this method.

self

This calculates the correcion due to self-absorption fluorescence experiment. It assumes that the sample is infinately thick and that the entry and exit angles of the photons are the same.

  $contents = {Y=>1, Ba=>2, Cu=>3, O=>7};
  ($amp_i0, $sigma_i0) = Xray::FluorescenceEXAFS->self($central, $edge, $contents);

It takes the central atoms tag, the alphanumeric edge symbol, and a reference to a hash which counts the atoms in the unit cell. It returns a list whose zeroth element is the multiplicative amplitude correction and whose first element is the sigma^2 correction in units of Angstrom squared.

overabsorption is an aliases for this method.

BUGS AND LIMITATIONS

Fourth cumulant corrections are not calculated.
Geometry and thickness effects are not included in the self absorption calculation

Please report problems to the Ifeffit Mailing List (http://cars9.uchicago.edu/mailman/listinfo/ifeffit/)

Patches are welcome.

AUTHOR

Bruce Ravel, http://bruceravel.github.io/home

http://bruceravel.github.io/demeter/

LICENCE AND COPYRIGHT

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.