Physicists have scored a major coup to nuclear physics with the discovery of Aluminum-20, a new three-proton-emitting isotope, as reported here at LPL! This exotic isotope, which exists past the proton drip line, has seven neutrons less than its more stable sister, Aluminum-27. The research explaining this major revelation was published in Physical Review Letters on July 10th. More significantly, it demonstrates the groundbreaking methodologies that allowed the researchers to identify this previously unknown nucleus.
This innovative collaboration—consisting of experimentalists and theoreticians from the Institute of Modern Physics (IMP) at the Chinese Academy of Sciences (CAS)—dramatized, highlighted and deepened a groundbreaking research initiative. They conducted their work at the Fragment Separator of the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. Their research sheds light on the complex decay pathways of isotopes found past the mysterious proton drip line. This fundamental research overwhelmingly increases our knowledge of nuclear structure and behavior.
Discovery Methodology
The scientists discovered Aluminum-20 with a pioneering in-flight decay method. With this method they were able to precisely determine angular correlations between the decay products of the radioactive isomer. This is particularly important in nuclear physics, especially when studying unstable isotopes that decay through less common processes.
Aluminum-20’s ground state first branches by emitting a proton to go to an excited state of Magnesium-19. The following decay of Magnesium-19 happens via a unique form of two-proton emission that occurs simultaneously. This three-step, multi-parent, multi-daughter decay process is an example of the delicate and complex relationships between isotopes at the edge of nuclear stability.
“This study advances our understanding of the proton-emission phenomena, and provides insights into the structure and decay of nuclei beyond the proton drip line,” – Xu.
Implications of Aluminum-20’s Characteristics
Aluminum-20 also has unusual features which set it apart from its more stable isotopes. With seven fewer neutrons than the stable Aluminum-27 isotope, its mere existence poses an affront to current theoretical paradigms on nuclear stability. The ground state decay energy of Aluminum-20 is significantly lower than predictions from isospin symmetry would imply. This difference suggests a potential breaking of isospin symmetry in both Aluminum-20 and its mirror sister, Neon-20.
Furthermore, Aluminum-20’s ground state spin-parity differs from that of Neon-20, as suggested by the best theoretical calculations available. This difference could dramatically change our view of nuclear interaction and stability. This is of particular relevance for isotopes found beyond the classical limits of stability.
“Aluminum-20 is the lightest aluminum isotope that has been discovered so far. Located beyond the proton drip line, it has seven fewer neutrons than the stable aluminum isotope,” – Associate Prof. Xu Xiaodong.
Significance in Nuclear Physics
With the discovery of Aluminum-20, the new record-holder, we have increased the total number of identified nuclides to more than 3,300. Fewer than 300 of these nuclides are stable and naturally occurring. This last finding underscores the importance of the advancement of experimental facilities in nuclear physics and detection technologies. These enhancements have enabled investigators to explore daringly unexplored realms of nuclear structure.
The ongoing exploration of isotopes like Aluminum-20 helps scientists refine their models and theories related to nuclear forces and decay processes. Each new innovation adds to the field and encourages more exploration into the most basic constituents of our universe.