Believed impossible, scientists manage to transform lead into gold
Researchers at the Large Hadron Collider (LHC), a 17-mile facility straddling the French-Swiss border, have observed a phenomenon previously relegated to the realm of alchemy: the momentary transformation of lead ions into gold. The finding, reported on July 30, 2025, stems from experiments involving collisions of ions at near light speed.
The Unexpected Creation of Gold
The analysis revealed that gold nuclei are produced during specific lead ion interactions with a frequency comparable to the rate of total hadronic collisions. This suggests that this “modern alchemy” occurs more often within the LHC tunnel than previously anticipated. Daniel Tapia Takaki, professor of physics at the University of Kansas and leader of the ALICE experiment team, explained that collider experiments typically focus on creating “lots of debris” from particle collisions.
Tapia Takaki’s team developed a method to detect events where ions merely graze each other, resulting in a remarkably clean interaction. These interactions produce a flash of light and an altered nucleus, with minimal other detectable particles.
How Does This Happen?
These transformations occur during “ultraperipheral collisions,” where atomic nuclei pass close to each other without direct contact. However, their powerful electromagnetic fields still interact. This interaction involves a burst of high-energy photons, described by the Weizsäcker Williams method, which can knock out protons from the lead nucleus. The loss of three protons results in a temporary gold-205 nucleus, lasting approximately 10⁻²³ seconds – just long enough to be detected.
Previous runs of the ALICE experiment hinted at these events, but the detector was initially optimized for head-on collisions. The team re-tuned the detector readouts and refined data analysis to isolate these events.
Implications for Physics and Future Colliders
Because photons carry no net charge, these interactions are free from the “spray of hadronic debris” that complicates other collision types. This clean environment allows physicists to study nuclear structure and test QED at previously unattainable energy levels. The team measured a gold production cross section of 6.8 barns, only 12 percent lower than the 7.67 barn rate for standard lead-lead interactions.
The analysis also revealed that knocking out even one proton transforms lead into thallium, which behaves differently in the LHC’s magnetic fields. Uncontrolled secondary particle beams, like those containing thallium, can disrupt operations and potentially damage sensitive components.
What’s Next?
The team plans to extend their analysis to include events with four and five proton emissions as more data from Run 3 becomes available. They are also collaborating with theorists to refine photonuclear models to better match observed neutron-to-proton ratios. A dedicated trigger for ultraperipheral collisions is under development, utilizing machine learning to capture these rare events more efficiently.
Frequently Asked Questions
What is a cross section in this context?
The analysis shows a gold production cross section of 6.8 barns, which is a measure of the probability of a specific interaction occurring. A higher cross section indicates a more frequent event.
What is the ALICE experiment?
ALICE is an experiment at the LHC designed to study the physics of strongly interacting matter at extreme energy densities, recreating the conditions that existed shortly after the Big Bang.
What other elements can be created in these collisions?
Beyond gold, near-miss collisions can also produce isotopes of mercury, thallium, or platinum, each offering unique insights into nuclear structure and decay paths.
Will a deeper understanding of these fleeting transformations ultimately contribute to more efficient and reliable operation of these complex scientific instruments?