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.\" ========================================================================
.\"
.IX Title "Xray::Absorption::Henke 3pm"
.TH Xray::Absorption::Henke 3pm "2022-06-28" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Xray::Absorption::Henke \- Perl interface to the Henke tables
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&   use Xray::Absorption;
\&   Xray::Absorption \-> load("henke");
.Ve
.PP
See the documentation for Xray::Absorption for details.
.SH "DESCRIPTION"
.IX Header "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.
.PP
The data in this module, referred to as \*(L"The Henke Tables\*(R", was
published as
.PP
.Vb 2
\&  B. L. Henke, E. M. Gullikson, and J. C. Davis,
\&  Atomic Data and Nuclear Data Tables Vol. 54 No. 2 (July 1993).
.Ve
.PP
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>.
.PP
The data is contained in a database file called \fIhenke.db\fR which is
generated at install time from the flat text files of the Henke data.
The data is stored in a Storable archive using \*(L"network\*(R" ordering.
This allows speedy disk and memory access along with network and
platform portability.
.PP
The required \f(CW\*(C`File::Spec\*(C'\fR, \f(CW\*(C`Chemistry::Elements\*(C'\fR, \f(CW\*(C`Storable\*(C'\fR,
modules are available from \s-1CPAN.\s0
.SH "METHODS"
.IX Header "METHODS"
The behaviour of the methods in this module is a bit different from
other modules used by \f(CW\*(C`Xray::Absorption\*(C'\fR.  This section describes
methods which behave differently for this data resource.
.ie n .IP """get_energy""" 4
.el .IP "\f(CWget_energy\fR" 4
.IX Item "get_energy"
Example:
.Sp
.Vb 1
\&   $energy = Xray::Absorption \-> get_energy($elem, $edge);
.Ve
.Sp
This behaves similarly to the \f(CW\*(C`get_energy\*(C'\fR method of the other
resources.  When using the Henke data resource, \f(CW$edge\fR 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.
.ie n .IP """cross_section""" 4
.el .IP "\f(CWcross_section\fR" 4
.IX Item "cross_section"
Examples:
.Sp
.Vb 1
\&   $xsec = Xray::Absorption \-> cross_section($elem, $energy, $mode);
\&
\&   @xsec = Xray::Absorption \-> cross_section($elem, \e@energy, $mode);
.Ve
.Sp
This behaves slightly differently from the similar method for the
McMaster and Elam resources.  The Henke tables are actually tables of
anomalous scattering factors and do not come with coherent and
incoherent scattering cross-sections.  The photo-electric
cross-section is calculated from the imaginary part of the anomalous
scattering by the formula
.Sp
.Vb 1
\&     mu = 2 * r_e * lambda * conv * f_2
.Ve
.Sp
where, \f(CW\*(C`r_e\*(C'\fR is the classical electron radius, lamdba is the photon
wavelength, and conv is a units conversion factor.
.Sp
.Vb 5
\&     r_e    = 2.817938 x 10^\-15 m
\&     lambda = 2 pi hbar c / energy
\&     hbar*c = 1973.27053324 eV*Angstrom
\&     conv   = Avagadro / atomic weight
\&            = 6.022045e7 / weight in cgs
.Ve
.Sp
The \f(CW$mode\fR argument is different here than for the other resources.
The options are \*(L"xsec\*(R", \*(L"f1\*(R", and \*(L"f2\*(R", telling this method to return
the cross-section or the real or imaginary anomalous scattering
factor, respectively.
.Sp
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.
.Sp
Because the Henke tables do not include the coherent and incoherent
scattering terms, the value returned by \f(CW\*(C`get_energy\*(C'\fR may be a bit
smaller using the Henke tables than that from the McMaster tables.
.SH "EDGE AND LINE ENERGIES"
.IX Header "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 \s-1NSLS\s0
and on the door of just about every hutch at \s-1NSLS\s0) is in the Henke
data resource.  The Henke data comes with the same, limited set of
fluorescence energies as McMaster.
.SH "BUGS AND THINGS TO DO"
.IX Header "BUGS AND THINGS TO DO"
.IP "\(bu" 4
It would be nice to improve the inter\-/extrapolation near absorption
edges.  As it stands, these tables produce really poor \s-1DAFS\s0 output.
.SH "AUTHOR"
.IX Header "AUTHOR"
.Vb 2
\&  Bruce Ravel, bruce@phys.washington.edu
\&  http://feff.phys.washington.edu/~ravel/
.Ve