NAME

       Xray::Absorption::Henke - Perl interface to the Henke tables

SYNOPSIS

          use Xray::Absorption;
          Xray::Absorption -> load("henke");

       See the documentation for Xray::Absorption for details.

DESCRIPTION

       This module is inherited by the Xray::Absorption module and provides access to the data
       contained in the Henke tables of anomalous scattering factors and line and edge energies.

       The data in this module, referred to as "The Henke Tables", was published as

         B. L. Henke, E. M. Gullikson, and J. C. Davis,
         Atomic Data and Nuclear Data Tables Vol. 54 No. 2 (July 1993).

       The Henke data is available on the web at http://www-cxro.lbl.gov/optical_constants/ and
       more information about the data can be obtained from Eric Gullikson <EMGullikson@lbl.gov>.

       The data is contained in a database file called henke.db which is generated at install
       time from the flat text files of the Henke data.  The data is stored in a Storable archive
       using "network" ordering.  This allows speedy disk and memory access along with network
       and platform portability.

       The required "File::Spec", "Chemistry::Elements", "Storable", modules are available from
       CPAN.

METHODS

       The behaviour of the methods in this module is a bit different from other modules used by
       "Xray::Absorption".  This section describes methods which behave differently for this data
       resource.

       "get_energy"
           Example:

              $energy = Xray::Absorption -> get_energy($elem, $edge);

           This behaves similarly to the "get_energy" method of the other resources.  When using
           the Henke data resource, $edge can be any of K, L1-L3, M1-M5, N1-N7, O1-O7, or P1-P3.
           Line energies are not supplied with the Henke data set.  The line energies from the
           McMaster tables are used.

       "cross_section"
           Examples:

              $xsec = Xray::Absorption -> cross_section($elem, $energy, $mode);

              @xsec = Xray::Absorption -> cross_section($elem, \@energy, $mode);

           This behaves slightly differently from the similar method for the McMaster and Elam
           resources.  The Henke tables are actually tables of anomalous scattering factors and
           do not come with coherent and incoherent scattering cross-sections.  The photo-
           electric cross-section is calculated from the imaginary part of the anomalous
           scattering by the formula

                mu = 2 * r_e * lambda * conv * f_2

           where, "r_e" is the classical electron radius, lamdba is the photon wavelength, and
           conv is a units conversion factor.

                r_e    = 2.817938 x 10^-15 m
                lambda = 2 pi hbar c / energy
                hbar*c = 1973.27053324 eV*Angstrom
                conv   = Avagadro / atomic weight
                       = 6.022045e7 / weight in cgs

           The $mode argument is different here than for the other resources.  The options are
           "xsec", "f1", and "f2", telling this method to return the cross-section or the real or
           imaginary anomalous scattering factor, respectively.

           The values for f1 and f2 are computed by linear interpolation of a semi-log scale.
           Care is taken to avoid the discontinuities at the edges.

           Because the Henke tables do not include the coherent and incoherent scattering terms,
           the value returned by "get_energy" may be a bit smaller using the Henke tables than
           that from the McMaster tables.

EDGE AND LINE ENERGIES

       The Henke data resource provides a fairly complete set of edge energies.  Any edge
       tabulated on the Gwyn William's Table of Electron Binding Energies for the Elements
       (that's the one published by NSLS and on the door of just about every hutch at NSLS) is in
       the Henke data resource.  The Henke data comes with the same, limited set of fluorescence
       energies as McMaster.

BUGS AND THINGS TO DO

       •   It would be nice to improve the inter-/extrapolation near absorption edges.  As it
           stands, these tables produce really poor DAFS output.

AUTHOR

         Bruce Ravel, bruce@phys.washington.edu
         http://feff.phys.washington.edu/~ravel/