apt [-v] [-h]
All energies in this program are in eV. All wavelengths are in Angstroms. All distances are in microns or centimeters as described above. The buttons labeled Clear, Help, and Exit do exactly what their labels suggest, although the Clear button only clears the currently displayed notecard. These have keyboard shortcuts of control-c, control-h, and control-q respectively. Control-t is the keyboard shortcut for toggling between energy and wavelength units.
If this program is invoked with a -v switch, version information is displayed to standard output and the program quits. If -h is given, this help document is displayed to standard output and the program quits.
This notecard is used to display edge and line energies of the elements and to make simple calculations of absorption legth and attenuation. When you click on an element in the periodic table, these data about that element are displayed in the notecard.
If an energy in eV is specified, then the absorption length of the selected element at the specified energy will also be displayed. If the selected element is a gas, the absorption length is given in centimeters, otherwise it is given in microns.
If a length is also specified in the box marks "thickness", then an attenuation factor will be given for a pure sample of that length and at the specified energy. For example, if you enter 8000 eV as the energy, and "10" as the thickness then select nickel, the attenuation will be 0.64. This means that a 10 micron nickel foil absorbs 36% of the incident beam. Again, centimeters are assumed for gases. With the thickness set to 10, selecting nitrogen gives an attenuation of 0.91 at that energy. This means that a 10 centimeter ionization chamber filled with nitrogen will absorb about 9% of the beam.
Not all of the data is available for all the elements. When data is missing, the corresponding space will be left blank. For transuranic elements, only the name and atomic number are displayed.
All data used in this program comes from the Elam data resource (see the Xray::Absorption manpage and the Xray::Absorption::Elam manpage). Of all the available xray absorption data resources, the Elam resource has by far the most complete collection of edge and line energies. The edge and line energies are organized into notecards. Click on the tabs of the notecards to see the different pages. The Siegbahn and IUPAC symbols for the fluorescence lines are displayed, along with the line energy and the relative intensity of the line. The relative intensity is normlized such that the sum of intensities from lines originating in the same core state sum to 1.
The weight displayed is the isotope-averaged atomic weight. The density is for the most common pure from of the element. The density displayed for carbon is the density of graphite. (Diamond has a specific gravity of about 3.1.) The densities of fluorine, and bromine are their liquid phase densities.
The third button from the left at the bottom of the screen is used to change the units displayed in the program between eV for energy and Ansgtroms for wavelength. Clicking this button will toggle all parts of the program between these two units. Please note that the entry box labeled Energy (or Wavelength) also toggles between the two units. When you have the program set to use wavelength, you must enter wavelength values in that box. If you enter a value that seems too small for energy units or too large for wavelength units, the program will pop open a confirmation dialog.
This notecard contains a simple interface to tables of anomalous scattering factors. Simply fill in an energy range and a value for the energy step and click on an element, and the f prime and double prime functions will be displayed in the canvas on the right. Alternatively, you can select an absorption edge and click on an element, and the anomalous scattering factors will be display 100 volts above and below that edge. You can even simply click on an element. If the element is lighter than cerium, the scattering factors around the K edge will be shown, other wise the scattering factors around the L3 edge are shown.
Below the widgets allowing you to specify the energy grid and the edge are two buttons. The one labeled Save data allows you to save the most recent calculation to a file. By default the filename is fpfpp_XX.dat, where XX is the symbol of the element for which the anomalous scattering was calculated. You can change the name of the output file in the file dialog.
The Clear range button is a bit more complicated. Because it is often useful to calculate the anomalous scattering factors of one element near the absorption edge of another element, the energy range is not cleared when you press on a new element button. Instead, the energy range used for the prior calculation is used for the new calculation. If, for example, you want the calculation made around an edge of the new element, you should hit the Clear range button or the Clear button at the bottom of the page.
The button which converts between wavelengths and energies currently does nothing when the anomalous scattering notecard is displayed.
While you certainly may specify very broad energy ranges, for example to see K and L edges for an element, do remember that perl is an interpreted language and that such a request will be rather time consuming even on a speedy computer.
Thanks to Stephane Grenier and Matt Newville for their helpful sugestions and beta testing.
Bruce Ravel, email@example.com http://feff.phys.washington.edu/~ravel copyright (c) 1999 Bruce Ravel