Several significant breakthroughs have been achieved by a team of researchers at the University of Tennessee, improving our comprehension of how heavy elements, such as gold and platinum, are synthesized across the cosmos. Their findings were published in the journal Physical Review Letters (PRL).
Heavy elements originate under extreme cosmic conditions, like those present during supernova explosions or the merging of neutron stars. This triggers the so-called r-process (rapid neutron capture), where atomic nuclei rapidly absorb neutrons. These nuclei progressively latch onto neutrons, leading to instability, before subsequently decaying and transforming into more stable elements.
However, many nuclei involved in this mechanism are exceedingly scarce, existing for mere fractions of a second, making direct investigation extremely challenging. To study these transformations, the physicists conducted experiments utilizing the ISOLDE facility at CERN.
The researchers tested rare indium-134 isotopes. The decay of this isotope resulted in the creation of excited states of tin isotopes: tin-134, -133, and -132. Expert analysis of the decay products was performed using a specialized neutron detector.
The primary achievement was the first-ever measurement of the energy of neutrons emitted via what is termed Beta-Delayed Two-Neutron Emission. This is an uncommon decay mode, observable only in highly unstable nuclei, and this measurement was accomplished by the specialists from the University of Tennessee.
The authors point out that quantifying such events is difficult because neutrons are easily scattered, making it hard in an experiment to discern whether a nucleus has released one neutron or two. Previous experimental efforts had entirely omitted measuring neutron energies, thus this novel methodology introduces extensive possibilities for future investigations.
A second key finding involves the initial observation of a neutron state within the tin-133 nucleus—a state long predicted by scientists but never before successfully detected. This represents an intermediate step in the two-neutron emission process.
It was previously hypothesized that following decay, a nucleus would rapidly “forget” its preceding configuration and simply eject neutrons for cooling purposes. The new data suggests, however, that the nucleus retains some residual information about its formation pathway.
The third discovery relates to a newly identified nuclear state that does not conform to the mechanisms predicted by current statistical models. This implies that our theoretical understanding of the characteristics of these unstable nuclei is currently incomplete.
These collected results will facilitate the refinement of r-process models, allowing for a more accurate description of heavy element creation during cataclysmic cosmic events.
Further research into unstable nuclei remains crucial. Such studies will enhance our deeper understanding of how chemical elements originate throughout the Universe and what precisely transpires during the most violent astrophysical occurrences.
About the Author
