NAME

Ifeffit::Demeter::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 Bruce Ravel (bravel AT bnl DOT gov)

Patches are welcome.

AUTHOR

Bruce Ravel (bravel AT bnl DOT gov)

http://cars9.uchicago.edu/~ravel/software/

LICENCE AND COPYRIGHT

Copyright (c) 2006-2008 Bruce Ravel (bravel AT bnl DOT gov). All rights reserved.

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

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.