New method for generating and directing X-rays

An artist’s impression of X-rays (purple) released by the new type of X-ray source, where a layered structure directing the beam is bombarded by electrons (yellow). Credit: Julius Hilbig

Physicists at the University of Göttingen develop a method in which beams are simultaneously generated and driven by a ‘sandwich structure’.

X-rays are usually difficult to direct and direct. X-ray physicists at the University of Göttingen have developed a new method by which X-rays can be emitted more accurately in one direction. To do this, scientists use a structure of thin layers of materials with different electron densities to simultaneously deflect and concentrate the generated rays. The results of the study were published in the journal Science Advances.

To generate X-rays in ordinary X-ray tubes, electrons that have been accelerated by a high voltage collide with a metal anode. Atoms in metal deflect and slow down electrons in their path, or electrons excite metal atoms to release radiation as they collide with each other. Both the deceleration of electrons and the excitation of metal atoms result in the emission of X-rays that are emitted. Unfortunately, the radiation is emitted evenly in all directions and then it is difficult to direct it in a focused beam. In addition, the front of the emitted X-ray waves is completely random and irregular.

Tim Salditt and Malte Vassholz

Tim Salditt (left) and Malta Vassholz. Credit: University of Göttingen

Physicists at the Institute for X-ray Physics at the University of Göttingen have now observed a new effect when the anode is replaced by a suitable structure of thin layers of materials with different electron densities. The thickness of the “sandwich structure” should be several million millimeters. If a particular layer sequence is selected, X-rays can be directed.

“When accelerated electrons hit this sandwich structure, the angular spectrum of the X-rays generated changes,” says Malte Vassholz, the first author of the paper. He goes on to say: “X-rays are preferentially created and run parallel to the layers, which act as a waveguide, similar to an optical fiber.”

Detailed numerical calculations allow the results to be reproduced in a model and calculated for a given choice of structure. “According to our calculations, the effect can be further improved by optimizing the structure. “This would allow us to generate X-ray radiation with a higher brightness,” adds Professor Tim Salditt.

The hope is that X-ray measurements, which until now have only been possible at large accelerators such as the electron synchrotron in Hamburg, can be brought ‘in the laboratory’ to some extent. “The applications of X-ray images to microscopically small, low-contrast objects – such as biological soft tissues – are particularly interesting,” says Salditt.

Reference: “Observation of characteristic electron-induced x-rays and radiation of the lung band from a guiding cavity” by Malte Vassholz and Tim Salditt, 22 January 2021, Advances in Science.
DOI: 10.1126 / sciadv.abd5677

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