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Medieval alchemists dreamt of turning lead into gold. At the Switzerland-based European Organization for Nuclear Research, known as CERN, scientists just did it, though not in a way that would fill a treasure chest.
Scientists observed lead atoms transforming into gold during high-speed near-collisions inside the Large Hadron Collider. While the gold existed for only a fraction of a second and in vanishingly small quantities, the experiment has offered a striking example of how extreme physics can change the identity of matter.
The research, published in Physical Review Journals by the ALICE collaboration, revealed that when lead nuclei raced past each other at nearly the speed of light inside the LHC, they generated powerful electromagnetic fields.
These near-miss encounters, where the nuclei didn’t collide directly but passed very close, sometimes knocked out three protons from a lead nucleus, turning it into a gold nucleus. Lead and gold have different numbers of protons in their nuclei, making them distinct elements; lead has 82 protons, whereas gold has 79.
Unlike the dreams of medieval alchemists, who believed that chemical processes could turn base metals into gold, this transformation was entirely nuclear. It relied on a process called electromagnetic dissociation, where a burst of photons ( or powerful particles of light) triggered changes in the nucleus, ejecting neutrons and protons.
To identify these rare events, the ALICE detector used its zero degree calorimeters to count how many protons and neutrons were ejected in each interaction. Emissions of three protons and at least one neutron pointed to the formation of gold. The team also recorded similar processes that produced thallium and mercury, which required the loss of fewer protons.
During LHC’s Run 2 between 2015 and 2018, the ALICE experiment estimated that 86 billion gold nuclei were formed. However, these nuclei fragmented almost instantly upon hitting the machine’s internal surfaces. The total mass of gold created was just 29 picograms — around one trillionth the mass of a human hair.
Even though the LHC has since ramped up its power and doubled gold production in Run 3, the total amount remains far too small for commercial use. “It is impressive to see that our detectors can handle head-on collisions producing thousands of particles, while also being sensitive to collisions where only a few particles are produced at a time, enabling the study of electromagnetic ‘nuclear transmutation’ processes,” Marco Van Leeuwen, ALICE spokesperson, said in a statement.
Beyond the fascination with gold, the study offered valuable insights into the physics of ultra-peripheral collisions and helped improve models that predict energy losses in particle accelerators, an important factor for designing future machines.
Uliana Dmitrieva of the ALICE collaboration in a statement said this analysis is the first to experimentally and systematically detect and study the signature of gold production at the LHC. “The results also test and improve theoretical models of electromagnetic dissociation which, beyond their intrinsic physics interest, are used to understand and predict beam losses that are a major limit on the performance of the LHC and future colliders,” added John Jowett, also of the ALICE collaboration.