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


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

       See the documentation for Xray::Absorption for details.


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

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

         C. T. Chantler
         Theoretical Form Factor, Attenuation, and Scattering Tabulation
            for Z = 1 - 92 from E = 1 - 10 eV to E = 0.4 - 1.0 MeV
         J. Phys. Chem. Ref. Data 24, 71 (1995)

       This can be found on the web at

       The Chantler data is available on the web at

       More information can be found on the personal web page of C.T. Chantler

       The data contained in a database file called chantler.db which is
       generated at install time from the flat text files of the Chantler
       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", and "Storable"
       modules are available from CPAN.


       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.


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

           This behaves similarly to the "get_energy" method of the other
           resources.  When using the Chantler data resource, $edge can be any
           of K, L1-L3, M1-M5, N1-N7, O1-O5, or P1-P3.  Line energies are not
           supplied with the Chantler data set.  The line energies from the
           McMaster tables are used.


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

           This behaves slightly differently from the similar method for the
           McMaster and Elam resources.  The Chantler tables contain anomalous
           scattering factors and the sum of the  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", "f2", "photo", and "scatter" telling
           this method to return the full cross-section cross-section, the
           real or imaginary anomalous scattering factor, just the
           photoelectric crosss-section, or just the coherent and incoherent
           scattering, respectively.

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


       The Chantler 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 Chantler data
       resource.  The Chantler data comes with the same, limited set of
       fluorescence energies as McMaster.


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


         Bruce Ravel,

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