Institute of Applied and technical Physics, Vienna University of Technology, Vienna, Austria
Non-withstanding the merits of distant-teaching, the package was primarily developed with the intent to assist a teacher present in a class of present
students, not to replace him/her. The main reason for this is, that for students of physics the context with basic principles should always be kept
alive, which requires active intercation with a class.
It might be interesting to note that programming the simulation of a more simplified analytical spectroscopical instrument (and data-evaluation) is
also part of a computer/software-oriented class given by the author. Great advantage was taken in the development of the discussed VXRF-package from
discussion with these students and several of them have mentioned their interest to participate in the further completion of VXRF.
Background.
X-ray fluorescence analysis (XRF) is among the most widely used industrial methods of chemical element analysis and therefore covered in most
university-classes on materials characterization for students of chemistry and physics. Compared to other spectroscopical methods in the infrared,
visible and ultraviolet ranges, its main advantage is that the excitation of fluorescent radiation in a specimen can be fully described by relatively
simple physical/mathematical ("fundamental parameter") models, which are independent of the chemical state of the involved atoms. Such models are
used frequently in practical applications for non-routine analytical problems, particularly for those where analyzed standards are not available
and for complex thin film structures. The alternative method is based on comparing the unknown with analyzed standards by using flexible
multi-dimensional fit-functions ("empirical parameter methods," "work-functions"), as in other spectroscopical methods. Empirical parameter
methods are naturally generally less suitable for explaining physical relationships.The package.
Virtual-XRF is a software package intended to provide a multimedia-based assistant for a teacher introducing XRF. Its main component is a virtual
(wavelength dispersive) spectrometer operated via a control panel with almost the full functionality of a real system. The virtual spectrometer
simulates fluorescent spectra based on fundamental parameter models combined with Monte-Carlo techniques, and an evaluation package displays
them and allows their qualitative as well as quantitative interpretation. Most experimental parameters can be set and varied by the user. For
example, vacuum conditions can be set in order to illustrate absorption of (softer) x-rays in air, counting time to study statistics, and furthermore
detectors, analyzer crystals, collimators (affecting beam divergence and resolution), and filters. Graphics routines illustrate important basic
relationships, such as spectra emitted from various types of x-ray tubes, as well as various fundamental parameters, such as photo-effect cross
sections, scattering cross sections, transition probabilities, Auger probabilities, emission line energies, and absorption edge energies as a
function of energy (or wavelength) and/or atomic number, as appropriate. Monte-Carlo simulations can be used to make photon (and electron) paths
visible, which is particularly illustrative in inhomogeneous specimens. The software is made available to all students of a class for copying to any
computers of their preference.
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