Scientists at CERN have achieved what medieval alchemists only dreamed of: turning lead into gold. Credit: SciTechDaily.com
An experiment has measured gold formation from lead nuclei during near-miss collisions in the Large Hadron Collider.
These high-speed interactions trigger electromagnetic processes that occasionally eject three protons, yielding gold atoms. Billions are made, but only for a split second.
Lead to Gold: A Modern Alchemical Feat at CERN
In a newly published study in Physical Review Journals, scientists from CERN’s ALICE experiment have observed something extraordinary: the transformation of lead into gold inside the powerful Large Hadron Collider (LHC).
For centuries, alchemists dreamed of turning lead into gold. Known as chrysopoeia, this ancient quest was based on the idea that both metals were heavy and shared similar properties. Of course, we now know that lead and gold are completely different elements, and no chemical process can turn one into the other.
A New Kind of Alchemy—Powered by Physics
In the 20th century, nuclear physics revealed that atoms could change from one element into another. This could happen naturally through radioactive decay or be triggered in laboratories using high-energy particles like neutrons or protons. Gold has been made this way before, but now, the ALICE team has measured a completely new method of element-changing magic—this time using near misses between high-speed lead atoms.
When two lead nuclei race through the LHC at nearly the speed of light, they sometimes just miss each other. Instead of colliding head-on, they pass close enough to trigger intense electromagnetic forces. These interactions can generate bursts of energy that change the very identity of atomic nuclei, including turning lead into gold.
Picture of the ALICE detector. Credit: CERN
Photon Bursts and Nuclear Shifts
The electromagnetic field emanating from a lead nucleus is particularly strong because the nucleus contains 82 protons, each carrying one elementary charge. Moreover, the very high speed at which lead nuclei travel in the LHC (corresponding to 99.999993% of the speed of light) causes the electromagnetic field lines to be squashed into a thin pancake, transverse to the direction of motion, producing a short-lived pulse of photons. Often, this triggers a process called electromagnetic dissociation, whereby a photon interacting with a nucleus can excite oscillations of its internal structure, resulting in the ejection of small numbers of neutrons and protons. To create gold (a nucleus containing 79 protons), three protons must be removed from a lead nucleus in the LHC beams.
“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,” says Marco Van Leeuwen, ALICE spokesperson.
Counting Gold Atoms in the Particle Smash
The ALICE team used the detector’s zero degree calorimeters (ZDC) to count the number of photon–nucleus interactions that resulted in the emission of zero, one, two and three protons accompanied by at least one neutron, which are associated with the production of lead, thallium, mercury and gold, respectively. While less frequent than the creation of thallium or mercury, the results show that the LHC currently produces gold at a maximum rate of about 89,000 nuclei per second from lead–lead collisions at the ALICE collision point. Gold nuclei emerge from the collision with very high energy and hit the LHC beam pipe or collimators at various points downstream, where they immediately fragment into single protons, neutrons, and other particles. The gold exists for just a tiny fraction of a second.
A Fleeting Treasure: Billion Gold Atoms, But No Jewelry
The ALICE analysis shows that, during Run 2 of the LHC (2015–2018), about 86 billion gold nuclei were created at the four major experiments. In terms of mass, this corresponds to just 29 picograms (2.9 ×10-11 g). Since the luminosity in the LHC is continually increasing thanks to regular upgrades to the machines, Run 3 has produced almost double the amount of gold that Run 2 did, but the total still amounts to trillions of times less than would be required to make a piece of jewellery. While the dream of medieval alchemists has technically come true, their hopes of riches have once again been dashed.
Beyond Gold: Improving Collider Physics
“Thanks to the unique capabilities of the ALICE ZDCs, the present analysis is the first to systematically detect and analyse the signature of gold production at the LHC experimentally,” says Uliana Dmitrieva of the ALICE collaboration.
“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,” adds John Jowett, also of the ALICE collaboration.
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DOI: 10.1103/PhysRevC.111.054906
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