Xray::Absorption::Henke(3pm)				User Contributed Perl Documentation			      Xray::Absorption::Henke(3pm)

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

       o   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/

perl v5.12.4							    2011-07-30					      Xray::Absorption::Henke(3pm)