Using light to describe the ancient world

Happy birthday XRF!

On this day in 1922, Lise Meitner described the principal behind x-ray fluorescence.

Meitner’s single authored paper, “Über die Entstehung der β-Strahl-Spektren radioaktiver Substanzen” [Google translate: “One the origin of β-ray spectra of radioactive substances”]  was published 90 years ago in Zeitschrift für Phsyik A: Hadrons and Nuclei. Although it is termed the ‘Auger effect’, and named for a French scientist who independently discovered it in 1923, this principle was first presented to the world in 1922 by the undersung Lise Meitner. The Auger effect can be used to measure elemental composition. In essence, x-rays are generated by an instrument and shot at a sample. Some of the incoming x-rays punch electrons out of the atoms in that sample, creating “gaps” in electron shells. Higher energy electrons in the same atom rush to fill these gaps, but they are too energetic – their extra energy is what got them promoted to the higher energy shells in the first place. These higher shell electrons lose this extra energy so that they can fit into the lower energy shells. The energy that is lost in this process is emitted in the form of an x-ray – an x-ray with an energy characteristic of the atom where all of this is taking place. By detecting these emitted x-rays, we can determine which atoms (i.e. elements) are present in the sample. So, x-rays in, different x-rays out, elemental composition revealed.

Energy dispersive x-ray fluorescence is a spectroscopy that is routinely used in studies of fossils. Much of this work relates to diagenesis. Living bone incorporates a broad array of elements, but most of these are at low concentrations. If a fossil bone is rich in certain elements, like uranium or iron, then it is likely that the fossil has had an intimate relationship with groundwater. Water can dissolve away useful biological components, like anions and their isotopic compositions, so it can be a good idea to assess the interaction between fossils and groundwater. We can do this with energy dispersive spectroscopy, thanks to Lise Meitner 90 years ago today.

Photo credit: BobPetUK. Images compile from here and here.


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