At CERN, the alchemists' dream, lead transformed into gold

The world's largest particle accelerator, the Large Hadron Collider at CERN , has realized the alchemists' dream: turning lead into gold . But the gold produced only existed for fractions of a second before breaking into protons and neutrons, a dynamic observed by detectors in the Alice experiment and described in detail for the first time in the study published in the journal Physical Review C.

For centuries it was believed that lead and gold were somehow two different forms of the same material, or that they were somehow connected, and for this reason it was thought possible to transform one into the other, but without success. Only in the 1900s, with the understanding of the structure of the atom, was the difference between the two elements understood, whose nuclei differed in the number of protons, 82 in lead and 79 in gold . But by accelerating their nuclei to speeds very close to that of light , LHC researchers have succeeded in recent years in doing what the alchemists were chasing, a transformation that has now been analyzed in detail thanks to the highly sensitive instruments of Alice , one of the 4 large detectors that are located along the path of the LHC.

By producing reactions called photon-nucleus interactions on lead nuclei, it was possible to ' expel ' some protons, thus producing nuclei of thallium, mercury and gold from lead . Reactions that were produced on several occasions, both during the so-called second Run of the LHC, i.e. the first session of activity of the large accelerator that took place between 2015 and 2018, and in the third Run. It is estimated that in the first occasion about 86 billion gold nuclei were created and more than double in the second, an apparently high quantity but which corresponds to a few billionths of a gram. Furthermore, those nuclei lasted only a few moments before fragmenting into a sort of rain of single protons and neutrons.