bionic (3) Xray::Absorption::Chantler.3pm.gz
NAME
Xray::Absorption::Chantler - Perl interface to the Chantler tables
SYNOPSIS
use Xray::Absorption;
Xray::Absorption -> load("chantler");
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
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
http://physics.nist.gov/PhysRefData/FFast/Text/cover.html
The Chantler data is available on the web at
http://physics.nist.gov/PhysRefData/FFast/html/form.html
More information can be found on the personal web page of C.T. Chantler
http://optics.ph.unimelb.edu.au/~chantler/home.html
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.
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 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.
"cross_section"
Example:
$xsec = Xray::Absorption -> cross_section($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.
EDGE AND LINE ENERGIES
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.
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/software/Absorption