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.