Physicists have measured a nuclear reaction that can occur in neutron star collisions, providing direct experimental data for a process that had previously only been theorised. The study, led by the University of Surrey, provides new insight into how the universe’s heaviest elements are forged — and could even drive advancements in nuclear reactor physics.
Working in collaboration with the University of York, the University of Seville, and TRIUMF, Canada’s national particle accelerator centre, the breakthrough marks the first-ever measurement of a weak r-process reaction cross-section using a radioactive ion beam, in this case studying the 94Sr(α,n)97Zr reaction. This is where a radioactive form of strontium (strontium-94) absorbs an alpha particle (a helium nucleus), then emits a neutron and transforms into zirconium-97.
The study has been published as an Editors Suggestion in Physical Review Letters.
Dr Matthew Williams, lead author of the study from the University of Surrey, said:
“The weak r-process plays a crucial role in the formation of heavy elements, which astronomers have observed in ancient stars — celestial fossils that carry the chemical fingerprints of perhaps only one prior cataclysmic event, like a supernovae or neutron star merger. Until now, our understanding of how these elements form has relied on theoretical predictions, but this experiment provides the first real-world data to test those models that involve radioactive nuclei.”
The experiment was enabled by the use of novel helium targets. Since helium is a noble gas, meaning it is neither reactive nor solid, researchers at the University of Seville developed an innovative nano-material target, embedding helium inside ultra-thin silicon films to form billions of microscopic helium bubbles, each only a few 10s of nanometres across.
Using TRIUMF’s advanced radioactive ion beam technology, the team accelerated short-lived strontium-94 isotopes into these targets, allowing them to measure the nuclear reaction under conditions similar to those found in extreme cosmic environments.
Dr Williams said:
“This is a major achievement for astrophysics and nuclear physics, and the first-time nanomaterials have been used in this way, opening exciting new possibilities for nuclear research.
“Beyond astrophysics, understanding how radioactive nuclei behave is crucial for improving nuclear reactor design. These types of nuclei are constantly produced in nuclear reactors, but until recently, studying their reactions has been extremely difficult. Reactor physics depends on this kind of data to predict how often components need replacing, how long they’ll last and how to design more efficient, modern systems.”
The next phase of research will apply the findings to astrophysical models, helping scientists to better understand the origins of the heaviest known elements. As researchers continue to explore these processes, their work could deepen our understanding of both the extreme physics of neutron star collisions and practical applications in nuclear technology.
