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.\"
.IX Title "Xray::Absorption::CL 3pm"
.TH Xray::Absorption::CL 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::CL \- Perl interface to the Cromer\-Liberman tables
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&   use Xray::Absorption;
\&   Xray::Absorption \-> load("cl");
.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 Cromer-Liberman tables of anomalous
scattering factors and line and edge energies.
.PP
The data in this module and the Fortran code which it calls as a
shared library, referred to as \*(L"The \s-1CL\s0 Tables\*(R", was published as
.PP
.Vb 2
\&  S. Brennan and P.L. Cowen, Rev. Sci. Instrum, vol 63,
\&  p.850 (1992)
.Ve
.PP
More information about these data is available on the Web at
.PP
.Vb 1
\&   http://www.slac.ssrl.stanford.edu/absorb.html.
.Ve
.PP
The values for the anomalous scattering factors are calculated by
calls to the Ifeffit library by Matt Newville.
.PP
The values of edge and line energies are contained in a database file
called \fIcl.db\fR which is generated at install time from the flat
text files of the these 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 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, $edge);
.Ve
.Sp
This behaves similarly to the \f(CW\*(C`get_energy\*(C'\fR method of the other
resources.  When using the \s-1CL\s0 data resource, \f(CW$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 \s-1CL\s0 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"
Example:
.Sp
.Vb 1
\&   $xsec = Xray::Absorption \-> cross_section($elem, $energy, $mode);
\&
\&   @xsec = Xray::Absorption \-> cross_section($elem, \e@energy, $mode);
.Ve
.Sp
For this data resource, one call in list context is considerably
faster than repeated calls in scalar context.  It is well worth the
trouble of organizing your code to make a single call in list context
and store the results for later use.
.Sp
This behaves slightly differently from the similar method for the
McMaster and Elam resources.  The \s-1CL\s0 tables are actually tables of
anomalous scattering factors and do not come with coherent and
incoherent scattering cross-sections.  The photo-electric
cross-section is calculated from the imaginary part of the anomalous
scattering by the formula
.Sp
.Vb 1
\&     mu = 2 * r_e * lambda * conv * f_2
.Ve
.Sp
where, \f(CW\*(C`r_e\*(C'\fR is the classical electron radius, lamdba is the photon
wavelength, and conv is a units conversion factor.
.Sp
.Vb 5
\&     r_e    = 2.817938 x 10^\-15 m
\&     lambda = 2 pi hbar c / energy
\&     hbar*c = 1973.27053324 eV*Angstrom
\&     conv   = Avagadro / atomic weight
\&            = 6.022045e7 / weight in cgs
.Ve
.Sp
The \f(CW$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 \s-1CL\s0 tables do not include the coherent and incoherent
scattering terms, the value returned by \f(CW\*(C`get_energy\*(C'\fR is a bit smaller
using the \s-1CL\s0 tables than using the others.
.SH "EDGE AND LINE ENERGIES"
.IX Header "EDGE AND LINE ENERGIES"
The \s-1CL\s0 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 \s-1CL\s0 data resource.
The \s-1CL\s0 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"
None that I know about...
.SH "AUTHOR"
.IX Header "AUTHOR"
.Vb 2
\&  Bruce Ravel, bruce@phys.washington.edu
\&  http://feff.phys.washington.edu/~ravel/software/Absorption
.Ve