Visualizing energy deposited by 35 MeV protons in lithium fluoride films on silicon

What is it about?

Lithium fluoride (LiF) is a salt which can host crystalline defects caused by the energy deposited in it by ionizing radiation (x-rays, gamma-rays, ions, protons, electrons, etc.). Some families of these defects emit red and green light when excited with blue light. Such a property is here exploited to visualize, for the first time in thin films of LiF over a silicon substrate, the energy-deposition profile (the "Bragg curve") of accelerated protons (energy of 35 MeV). Our work demonstrates that the substrate material and the proton-beam grazing angle heavily influence the shape of the Bragg curve.

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Photo by Misael Moreno on Unsplash

Photo by Misael Moreno on Unsplash

Why is it important?

Our findings demonstrate that a LiF film can store a photoluminescent image, induced by the energy released by impinging protons, whose maximum-intensity region (the "Bragg peak") is located in a position determined by the characteristics of the underlying substrate. Therefore, by observing the LiF film, one can experimentally visualize where protons release most of their energy in the substrate material, something that otherwise would be not possible by optical means. Information on the Bragg-peak positions allows estimating the energy of the proton beam.