FEPA News

FEPA NEWS 45 47 Developments in Philately Energy Dispersive X-Ray Fluorescence Spectroscopy (ED-XRF) Spectroscopic and chemical examinations of the red and brown vignettes of the Orient Express Ute Dorr FRPSL and Dr. rer. nat. Elmar Dorr FRPSL write: 1 This examination arises from a question addressed by Prof. Dr. Ulrich Ferchenbauer in the fourth volume of his Austria Monography. Was there a brown vignette of the Orient Express or is this a result of environmental influences? Ferchenbauer speaks of oxidation. 2 The scientific method 2.1 Spectroscopy of the red colour With the help of modern spectroscopy, which made possible a non-destructive examination of the vignette, so that no parts of the vignette had to be dissolved and thus irreparably lost, the method presented here leaves the vignette undamaged and in its original condition. It is based on the fact that atoms of a chemical element each have a distinctive electronic structure. This electronic structure (as, by the way, also the structure of the nucleus of the atom) is characterised by the position of the element, and thus the atom representing it, in the “Periodic System of the Elements” (PSE). The Danish physicist, Nils Bohr, recognised this at an early stage and used this knowledge to formulate his findings in the similarly named atom model, in that he postulated the energy level of the electrons as shells around the atomic nucleus. The nearer the shell, in which the electron is located, is to the core of the atom, the lower is its (electron) energy. Therefore, the electron shell further out represents correspondingly higher energy levels – always depending on the distance from the core of the atom. From Konrad Röntgen’s work, we know that electrons of the lowest energy level – the electrons which are the closest to the atomic nucleus – can be knocked out of this shell through high-energy radiation (high-energy electrons or also X-radiation). One then speaks of a K-electron emission. One may say that a hole then occurs in the K-shell and an electron from the next shell (next higher energy level) – that of the L-shell – can now leave its higher energy level and occupy a place in the energetically more favourable, and thus more stable, K-level. The atom concerned emits the difference in energy () between the K- and L-shells in the form of X-radiation (characterised by the wavelength and frequency (), where h is the Planck effect quantum and c the speed of light in a vacuum) which can be measured by an energy-dispersive spectrometer. We thus get a characteristic X-ray fluorescence spectrum. The following illustrations present the above principle schematically: Fig. 1a: Schematic energy level (term scheme) of an atom for the energy difference between the L- and K-shells