A team of scientists from the Institute of Modern Physics, Chinese Academy of Sciences, discovered an unprecedented atomic nucleus - aluminum-20 at the GSI Heavy Ion Research Center in Germany. This discovery has completely rewritten human understanding of the atomic decay process. This extremely unstable isotope decays through an unprecedented three-proton sequential emission process, not only challenging long-standing basic assumptions about nuclear structure, but also possibly revealing the breaking of fundamental symmetry in atomic particles.
Aluminum-20 is the lightest aluminum isotope ever discovered, located beyond the proton drip line, and it has seven fewer neutrons than stable aluminum isotopes. This extreme neutron-deficient state makes it an ideal subject for exploring the boundaries of nuclear stability. The research team used the flight decay method, successfully confirming the existence of aluminum-20 and observing its unique decomposition process by measuring the angular patterns of emitted particles during the decay process.
A newly discovered aluminum isotope ejects three protons in a rare sequence, rapidly self-destructing and shaking our understanding of atomic decay. Source: Shutterstock
The research findings were published in the "Physical Review Letters" on July 10, marking an important milestone in the field of nuclear physics. This is the first time scientists have observed the phenomenon of "three-proton decay chain," opening up new research directions for understanding the behavior of extreme nuclides.
Breakthrough Decay Mechanism
Traditional radioactive decay processes are relatively simple, usually involving the emission of a single type of particle. However, the decay process exhibited by aluminum-20 is extremely complex and dramatic. Through detailed analysis of angular correlations, researchers found that the ground state of aluminum-20 first decays into the intermediate ground state of magnesium-19 by emitting a proton, and then the ground state of magnesium-19 undergoes subsequent decay by simultaneously emitting two protons.
Xu Xiaodong, a postdoctoral researcher at the Institute of Modern Physics, Chinese Academy of Sciences, and the first author of the study, explained, "Aluminum-20 is the first observed three-proton emitter, and its single-proton decay daughter nucleus is a two-proton radioactive nucleus." This unique decay pattern breaks the traditional framework of nuclear physics and provides a new perspective for studying the structure and decay of nuclei beyond the proton drip line.
More importantly, the researchers found that the decay energy of the ground state of aluminum-20 is significantly less than the predicted value inferred by isospin symmetry. This suggests that there may be isospin symmetry breaking in aluminum-20 and its mirror partner neon-20. This finding is supported by the most advanced theoretical calculations, which predict that the spin-parity of the ground state of aluminum-20 differs from that of the ground state of neon-20.
New Frontiers in the Study of Extreme Nuclides
Three-proton emission diagram of aluminum-20. Signature: Xu Xiaodong
The significance of this discovery goes beyond the discovery of a single isotope. Among the 3,300 or so known nuclides, only about 300 are stable and naturally occurring. The rest of the unstable nuclides undergo radioactive decay. In the mid-20th century, scientists discovered common decay modes, including alpha decay, beta decay, electron capture, gamma radiation, and fission.
However, in recent decades, due to the significant development of nuclear physics experimental facilities and detection technologies, scientists have discovered several strange decay modes when studying nuclides far from stability, especially in neutron-deficient nuclides. In the 1970s, scientists discovered single-proton radioactivity; in the 21st century, double-proton radioactivity was found in the decay of some extreme neutron-deficient nuclides; recently, even rarer phenomena such as three-proton, four-proton, and five-proton emissions have been observed.
The discovery of aluminum-20 has taken this research to a new height. Xu Xiaodong pointed out, "This study has promoted our understanding of proton emission phenomena and provided new insights into the structure and decay of nuclides beyond the proton drip line."
Scientific Achievements through International Collaboration
This breakthrough research is the result of international collaboration, involving scientists from the Institute of Modern Physics, Chinese Academy of Sciences, the GSI Research Center in Germany, Fudan University, and more than ten other institutions. The experiment was conducted at the GSI Heavy Ion Research Center's fragment separator facility, utilizing world-leading nuclear physics research equipment.
The study was supported by multiple funding programs, including the National Key R&D Program of China, the Chinese Academy of Sciences' President's International Fellowship Initiative, and the National Natural Science Foundation of China, reflecting China's continuous investment in basic scientific research and the increasing international influence.
This discovery not only advances human understanding of the basic structure of atomic nuclei, but also opens up new directions for future nuclear physics research. By studying these extreme condition atomic nuclei, scientists can better understand the process of element formation in the universe and the nuclear reaction mechanisms inside stars.
The Perfect Combination of Theory and Experiment
The discovery of aluminum-20 also demonstrates the importance of combining theory and experiment in modern nuclear physics research. The research team not only successfully observed this rare decay phenomenon, but also conducted in-depth analysis and explanation of the experimental results through advanced theoretical calculations.
The discovery of this multi-proton emission phenomenon provides new experimental evidence for understanding the nature of nuclear forces and the stability mechanism of nuclear structure. At the same time, the observation of isospin symmetry breaking also provides important experimental constraints for the further development of nuclear physics theory.
With the continuous advancement of experimental technology and the improvement of theoretical models, scientists expect to discover more similar exotic nuclides in the future, further expanding human understanding of the fundamental laws of the material world. The discovery of aluminum-20 marks a new stage in nuclear physics exploration, providing unprecedented insights into the behavior of the most basic building blocks of the universe - atomic nuclei.
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