The writer is a scientific commentator
For more than a decade, a remarkable facility has been taking shape in southern Sweden. The European Spallation Source, which is nearing completion in Lund and is funded by 13 European countries including the UK, will use the world's most powerful linear proton accelerator to produce the world's most powerful neutron source.
This is very important for science: neutrons, the electrically neutral particles that exist alongside positively charged protons in the nucleus of an atom, can be used to explore the nature and structure of materials, just as X-rays once revealed the double helical structure of the atom. DNA. There are many neutron facilities around the world, including the United States, the United Kingdom, and Japan.
But the superpower of ESS, which will undergo initial testing this year in preparation for experiments starting in 2026, may also provide a glimpse of something special: a neutron transforming into its antimatter equivalent, an antineutron. Discovering this could solve one of the biggest mysteries in fundamental physics: why is there more matter than antimatter in the universe?
“We shouldn’t be there,” Valentina Santoro, a particle physicist and chief scientist at ESS, told me. She explains that the Big Bang should have produced equal amounts of matter and antimatter, which then cancel each other out. “So, perhaps after the Big Bang, the majority of the universe was wiped out and only a little matter was left.”
The challenge is explaining the leftovers. One possibility is that matter can “oscillate” into antimatter and vice versa, and that this process somehow led to the excess we see today. Even individual observation of such a neutron conversion would be a Nobel Prize.
Neutrons, which scatter from nuclei like balls swinging on a billiard table, have long been used to look into the heart of matter and matter. Scientists can infer the shapes and sizes of particles and crystals by pointing neutrons at them, and measuring how the particles change energy, speed and direction after colliding. The more intense the neutron beam, the more detailed the structural information. In preparation, a data and software management center is being built in neighboring Denmark; The two Nordic countries are the main contributors to the €3.5 billion cost.
Neutrons have advantages over x-rays and electrons, such as being non-destructive. This makes it a valuable tool for examining fragile artifacts. In 1991, researchers at Oak Ridge National Laboratory in Tennessee used neutrons to study hair samples from Zachary Taylor, the 12th president of the United States, to refute theories that he was killed by arsenic poisoning.
Neutrons can also “see” small atoms such as hydrogen, making them useful for studying samples such as fuel cells. Its magnetic spin can be harnessed to probe magnetic materials. One planned application, for example, is the development of more sensitive magnetic resonance imaging (MRI) scanners, used in cancer detection.
However, regulating neutrons is not an easy task; It requires the division of atomic nuclei. This cracking can be done by nuclear reactors, or, as in the case of ESS, by a process known as nuclear fragmentation. The latter involves accelerating protons to almost the speed of light, then ramming them into a heavy metal target (the ESS target is a rotating disk containing three tons of tungsten). This collision causes the neutrons to be “split up” or ejected. The liberated neutrons are then slowed down, cooled and directed for scientific use. Because of the limitations of the reactor, fragmentation is viewed as the future of neutron science.
Santoro says the ESS facility will operate at 2 megawatts initially, twice the power of current sources; It will then rise to 5 megawatts, producing 10 billion trillion neutrons annually. A more intense neutron beam should provide higher-resolution results and speed up experiments; The facility is expected to accelerate the development of more efficient batteries and environmentally friendly plastics. Particle physicists around the world are also working to integrate ESS into future research plans, with the “big science” facility seen as a complement to CERN in Geneva.
Santoro and his colleagues need just one of those countless neutrons to transform into an antineutron, creating a distinctive high-energy signature. “It's like flipping a huge number of coins, but we only need one signal,” she says, expressing hope that three or four years of process could lead to a jackpot, as well as discrete insights into phenomena like dark matter.
Amid a coming celebration of neutron science — in biology, chemistry, materials science, drug development, and archaeology — we may one day learn how our universe began as a cosmic remnant.
