The ALICE experiment at the Large Hadron Collider (LHC) investigates the outcomes when heavy ions collide. Primarily, this research aims to comprehend the quark-gluon plasma that was present during the earliest instants following the Big Bang. However, colliding lead ions can also decompose these atoms into more familiar elements, like transforming lead into gold.
This process isn’t about transforming lead into gold through alchemical means; rather, it involves nuclear transmutation. Lead contains 82 protons along with approximately 126 neutrons within its nucleus. In contrast, gold consists of only 79 protons—three less than lead. To achieve this transformation, you would need to remove three protons from every single lead atom.
The Large Hadron Collider (LHC) isn’t designed for this purpose, but by colliding lead nuclei at 99.999993 percent of the speed of light, you can produce intriguing outcomes. Not every single nucleus will collide with another; hence, there will still be free-moving lead ions circulating within the collider. The intense electromagnetic fields inside the LHC have the potential to generate fleeting yet potent bursts of radiation, which could strip away three protons from each lead ion, effectively transforming them into gold nuclei. This transformation process is particularly thrilling because it allows us to observe these events directly.
It’s remarkable how our detectors manage both head-on collisions that generate thousands of particles and those with just a few particles emerging sequentially,” noted Marco van Leeuwen, the ALICE spokesperson. “This sensitivity allows us to investigate rare electromagnetic ‘nuclear transmutation’ phenomena.
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The focus was not solely on gold. The researchers utilized the detector’s zero-degree calorimeters (ZDC) to examine collisions involving high-energy photons and the nuclei of lead ions. Their objective was to observe emissions consisting of zero, one, two, and three protons along with a missing neutron. What they discovered were reactions resulting in lead deficient in neutrons as well as the presence of elements such as thallium, mercury, and gold.
While gold appears less often, each collision generates approximately 89,000 gold nuclei per second from among the 174 billion lead atoms within the beam. However, this won’t spark a gold rush at CERN. Despite being an almost immeasurable amount—amounting to just a tiny fragment of a gram—the gold particles ultimately collide with great force against the walls of the accelerator, causing them to disintegrate.
“Thanks to the distinctive features of the ALICE ZDCs, this current analysis marks the first time we have systematically detected and examined evidence of gold production at the LHC through experimental means,” said Uliana Dmitrieva from the ALICE collaboration.
“The findings further validate and refine theoretical models of electromagnetic dissociation. These models, apart from their inherent scientific importance, help us comprehend and forecast beam losses, which significantly constrain the efficiency of the LHC and upcoming particle accelerators,” explained John Jowett, who is part of the ALICE collaboration as well.
The details of the work are published in
Physical Review C
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