–With a feat harking back to ancient alchemist fantasies, physicists in CERN’s Large Hadron Collider (LHC) have succeeded in transforming lead into gold. Using the sophisticated ALICE (A Large Ion Collider Experiment) detector, researchers measured the production of some 86 billion nuclei of gold during 2015-2018 LHC. Though gold made weighs an infinitesimal 29 picograms—trillionths of a gram—and persists for fractions of a second, this achievement is one for modern nuclear physics, providing profound insight into particle collision and elemental forces shaping our universe. Released today in Physical Review C, May 7, 2025, these findings not only realize a centuries-long dream but advance understanding of nuclear transmutation and electromagnetic interactions at speeds approaching light.
The Alchemy Dream Encounters Modern Science
Alchemists for centuries pursued chrysopoeia, a legendary alchemy by which base metals would transform themselves into gold, through primitive chemical manipulation and magical incantations. Their quest, despite being driven out of curiosity for nature’s secrets, was bound for failure under the limits of medieval science. Today, physicists have achieved that vision—not using potions or philosopher’s stones but using the earth’s most massive particle accelerator, CERN’s 27-kilometer circumference underground tunnel under the France-Switzerland border.
The LHC accelerates heavy ions, including lead nuclei, to dizzyingly high speeds—99.999993% of light speed—in circumstances where matter’s fundamentals can be toyed around with. Lead has 82 protons and an atomic number 82, gold 79 protons and an atomic number 79. These are tantalizingly proximate in the periodic table. Take a few protons and neutrons out of a lead nucleus and scientists can make a gold nucleus in essentially converting one element into another. The act of nuclear transmutation requires colossal amounts of energy and accuracy only in a place like the LHC, at the limits of what mankind can technologically achieve.
The Process: From Lead to Gold
The gold was formed in the ultra-peripheral collisions (UPCs), which are a type of interaction in the LHC where lead nuclei pass each other by without colliding head-on. The 82 protons in one lead nucleus at these relativistic speeds produce an intense electromagnetic field aligned perpendicularly to the direction of motion of the nucleus by relativistic effects. When lead nuclei pass by one another, this field generates a burst of virtual photons—light-like particles that are charged with electromagnetic energy.
These photons can interact with a different lead nucleus and excite the nucleus’ internal structure and cause electromagnetic dissociation. The nucleus becomes unstable and ejects some protons and neutrons in doing this. When a lead-208 nucleus (82 protons, 126 neutrons), for instance, loses three protons and two neutrons, a gold-203 nucleus (79 protons, 124 neutrons) results. This is a nuclear reaction rather than one of chemistry, rearranging the atom’s identity.
One of the nine LHC experiments, the ALICE detector played an intrinsic part in observing this event. The Zero Degree Calorimeters (ZDCs) of the detector are placed remotely from where collisions occur and can detect particles ejected near zero degrees relative to the direction of the beam. Through counting the number of emitted protons (0, 1, 2, or 3) in conjunction with one or more neutrons, the collaboration in ALICE discovered the following products
- 0 released protons: Lead remains lead.
- Releasing 1 proton: Thallium (81
- 2 protons emitted: Mercury (80 protons).
- 3 protons emitted: Gold has 79 protons.
This accurate count allowed scientists to determine the production of gold in a rate of around 89,000 nuclei per second in lead-lead collisions near the collision point in ALICE. “Due to the special properties of the ALICE ZDCs, this measurement is the first experimental investigation of the gold production signature in a systematic manner in an LHC experiment,” notes ALICE physicist Uliana Dmitrieva.
A Passing Glint: The Truth of the Gold
Its dazzling makeover comes with serious caveats. The number of gold nuclei created—86 billion—is a paltry 29 picograms, an amount that is given in units of bacteria. To place it in context, a gram of gold contains sextillions (10^21) of atoms, making the output of the LHC minuscule by any useful measure. Even more strikingly, the gold nuclei last but microseconds before impacting the LHC beam pipe or collimators and being shredded into a burst of protons, neutrons, and electrons.
Such a fleeting existence would have dismayed medieval alchemists who were seeking to amass material wealth. The procedure is also astoundingly inefficient, taking a multi-billion-dollar particle accelerator, enormous amounts of energy, and highly advanced apparatus. As compared to conventional means of gold procurement—mining it, refining it from ore, or even recycling it, for that matter—the LHC’s method is the least practical possible. So the experiment is hardly about creating gold for profit and rather about revealing mysteries of the subatomic world.
Byproducts and Broader Outcomes
Gold was not the only product in these collisions. The thallium (81 protons) and mercury (80 protons) were formed in significantly larger amounts since expelling fewer protons is more probable. The fact that these products are separated out by the detector is a function of the resolution of the ALICE detector in being able to handle high-multiplicity collisions that produce thousands of particles as well as infrequent events that produce a small number of particles.
It is incredible that our detectors can handle head-on collisions that produce thousands of particles and simultaneously are sensitive in collisions where a few particles are produced in a single event and thus enable one to probe rare electromagnetic ‘nuclear transmutation’ processes,” particle physicist Marco van Leeuwen from Utrecht University and spokesperson for the ALICE collaboration told.
The principal scientific merit of the experiment is the refinement of electromagnetic dissociation models that describe nuclei emitting particles in highly energetic environments. These models are crucial for determining beam losses in particle accelerators, one of the key performance limitations for these instruments. With measurement of gold, thallium, and mercury production, the ALICE collaboration provides data that can help future colliders be optimized in design in order that more difficult experiments can examine the underlying properties of the universe.
Historical Background: From Alchemy To Nuclear Physics
Transmutation of lead into gold is not new. As far back as 1980, a Nobel laureate Glenn Seaborg conducted the same procedure by bombarding bismuthic nuclei with high-energy particles, and lead-to-gold transmutations were carried out in 2002-2004 in CERN’s Super Proton Synchrotron. The innovation in the experiment in ALICE is in systematic recording of gold formation in ultra-peripheral collisions using the record energy of the LHC and in the accuracy of ZDCs.
This achievement resonates throughout nuclear physics’ broader history as well. Alchemists had attempted gold through chemistry before, but science knows nowadays that transmutation is about altering the nucleus—a 20th-century breakthrough through radioactivity and nuclear reaction discovery. The LHC manipulation of nuclei in velocities close to that of light is the ultimate expression of this process well beyond what even our medieval predecessors dreamed.
Implications for Science and Beyond
The results of the ALICE experiment in Physical Review C (DOI: 10.1103/PhysRevC.111.054906) provide several contributions
- Nuclear Physics: The results validate models of photon-nucleus interactions that are key in understanding nuclei under extreme conditions.
- Accelerator Technology: More efficient and longer-lived particle accelerators would result from improved electromagnetic dissociation models, enabling even more accurate experiments.
- Astrophysics: Interactions between photons and nuclei are employed in processes such as nucleosynthesis in stars wherein nuclear processes produce heavy elements.
- Fundamental Research: Though its long-term goal is studying quark-gluon plasma, an earlier state of matter in the universe, these findings indicate versatility in detection device.
Aside from their technical significance, the results amaze the imagination. The transformation of lead into gold even from microscopic dimensions crosses hopes in days of yore and science in the present times and reminds one about mankind’s ancient pursuit after a mastery and comprehension of nature.
The Larger Context: CERN’s Mission The CERN
The Large Hadron Collider is an international collaboration of nearly 10,000 scientists from over 100 countries. Experiments CMS, ATLAS, ALICE, and LHCb are attempting some of the most profound unsolved mysteries of the universe from the composition of the Higgs boson particle to what matter does when heated and compressed to extreme temperatures and densities. The 10,000-tonne device 56 meters underground near St Genis-Pouilly in France, the ALICE detector, is specifically designed for analyzing heavy-ion collisions recreating conditions a fraction of a second after the Big Bang. Although CERN’s gold-creation experiment is a fascinating sideline of its work, it is indicative of what CERN does overall: pushing the frontiers of human knowledge. Being able to identify and measure obscure nuclear transformations is a testament to the LHC’s record-breaking precision and the brilliance of its sensors, and it opens the door to discoveries down the line that may someday rewrite our understanding of the universe. Conclusion: A Golden Moment in Science It is a milestone of science that mixes frontier physics and historical romance in its alchemy of transforming lead into gold. Though its 29 picograms of gold product are fleeting and worthless, its real worth comes from what it accomplishes for nuclear physics, accelerator technology, and for what we know of the subatomic realm. By measuring gold production in ultra-peripheral collisions in an orderly fashion, the collaboration has achieved not just an alchemist’s fantasy but has moved the frontier of humanity’s knowledge. As we gaze in awe at this new alchemy, we are awestruck by the capability of the LHC in piercing into matter and energy’s unseen worlds and enabling us to glimpse what underlies our universe. To scientists as well as dreamers, it is proof of a boundless quest for discovery—one nucleus at a time.
