Scientists Discover First-ever Three-Proton Emission from Aluminum-20
Darmstadt, Germany – In a groundbreaking revelation that pushes the boundaries of nuclear physics, an international team of researchers has observed and characterized the first instance of three-proton emission from the newly identified, highly unstable isotope, aluminum-20. This rare decay mode offers unprecedented insights into the structure of atomic nuclei existing far from the familiar “valley of stability.”
The study, published in the prestigious journal physical Review Letters, details the experimental observation of aluminum-20, an isotope with seven fewer neutrons than its stable counterpart. Located beyond the proton drip line – a theoretical boundary indicating an excess of protons – aluminum-20’s decay provides a unique window into nuclear forces and configurations.
Utilizing an advanced in-flight decay technique at the GSI Helmholtz Center for Heavy Ion Research, scientists meticulously measured the angular correlations of aluminum-20’s decay products. Their analysis revealed a complex, sequential decay process. Aluminum-20 first emits a single proton, transforming into magnesium-19. This intermediate nucleus then undergoes a simultaneous emission of two protons, completing the three-proton decay. This marks the first observed three-proton emitter where the daughter nucleus itself is a two-proton radioactive species.
Further analysis of the decay energy revealed a critically important deviation from predictions based on isospin symmetry. This discrepancy suggests a potential breaking of isospin symmetry within aluminum-20 and its mirror nucleus, neon-20. This finding is bolstered by theoretical calculations that indicate a difference in the spin-parity of the ground states of these two nuclei.
“This study considerably advances our understanding of proton-emission phenomena and provides crucial insights into the structure and decay mechanisms of nuclei situated beyond the proton drip line,” stated Associate Professor Xiaodong Xu from the Institute of Modern Physics (IMP) of the chinese Academy of Sciences (CAS), the lead author of the study.
While over 3,300 nuclides have been identified, only a fraction are stable. The vast majority are unstable and undergo radioactive decay. While common decay modes like alpha and beta decay have been understood for decades, the advancement of refined experimental facilities and detection technologies has enabled the discovery of more exotic decay processes in recent years. Single-proton radioactivity was first observed in the 1970s, followed by two-proton emission in the early 21st century. The current discovery of three-proton emission represents a further step into the realm of extremely rare nuclear decay phenomena.
This significant research was a collaborative effort involving the IMP, GSI, Fudan University, and over a dozen other institutions, underscoring the global nature of cutting-edge scientific exploration.