Researchers from Tokyo institute of Technology in Japan discovered a new oxygen isotope, oxygen-28, which has defied anticipated behavior. Having the greatest neutron count in oxygen nuclei, it unexpectedly undergoes rapid decay. This unsettles our understanding of nucleus particle "magic" numbers.
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Discovering Oxygen-28 Isotope
Within an atom's nucleus is the nucleon, which comprises the protons and neutrons. An element's atomic number derives from its proton count, while neutron count varies.
Isotopes, distinct in neutron numbers, characterize elements; for instance, oxygen with 8 protons exhibits variable neutron quantities. Formerly, the highest neutron count observed, 18, existed in oxygen-26, where 8 protons coupled with 18 neutrons, summing to 26 nucleons.
Recently, a group headed by nuclear scientist Yosuke Kondo at Tokyo Institute of Technology uncovered unfamiliar oxygen isotopes: oxygen-27 and oxygen-28, containing 19 and 20 neutrons correspondingly. This research took place at RIKEN Radioactive Isotope Beam Factory, a cyclotron accelerator aiming to generate unsteady isotopes.
In the study, titled "First observation of 28O" published in the journal Nature, scientists initiated the process by directing calcium-48 isotopes at a beryllium target, leading to the creation of lighter atoms, including fluorine-29-an isotope containing 9 protons and 20 neutrons.
Subsequently, fluorine-29 was collided with a liquid hydrogen target, aiming to eject a proton and produce oxygen-28. Successful, this effort revealed an unexpected outcome. Oxygen-27 and oxygen-28 both proved unstable, existing briefly before transforming into oxygen-24, along with 3 or 4 free neutrons. This observation holds intriguing implications for oxygen-28.
Notably, the numbers 8 and 20 are regarded as "magic" numbers for protons and neutrons respectively, implying stability for oxygen-28. The total of these particles depends on how the addition of each nucleon impacts the balance within proton and neutron configurations known as 'shells'.
In nuclear physics, a magic number signifies the quantity of nucleons that fills a shell, characterized by a distinct energy gap from the preceding shell. A nucleus with both proton and neutron shells holding these magic numbers is termed doubly magic, implying heightened stability.
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Oxygen-28 Presents a Broader Puzzle
The prevalent form of oxygen on Earth, including the air living things respire, is the doubly magic variation known as oxygen-16. Despite expectations, the elusive oxygen-28 was regarded as the next doubly magic isotope in the oxygen series after oxygen-16.
Intriguingly, the concept of oxygen-24 being doubly magic turns up in 2009, potentially shifting the focus to 16 as a magic number. However, Yosuke Kondo's recent findings have introduced a significant twist by suggesting that the neutron shell in oxygen-28 was not fully occupied, raising doubts about 20 being a magic number.
This pattern of observation mirrors a curious trend noticed in isotopes of neon, sodium, and magnesium, where the 20-neutron shell doesn't attain full closure. This anomaly extends to fluorine-29 and, importantly, oxygen-28.
Kondo's research proposes an explanation for this occurrence, implying that the neutron shell in oxygen-28 remained incompletely filled, prompting questions about whether 20 can truly be considered a magic number for neutrons.
Exploring the enigma of this neutron shell involves further investigation into the nucleus's excited state. Uncovering alternative techniques for producing oxygen-28 might yield deeper insights, although such endeavors present notable challenges.
Kondo's team has initiated a paradigm shift, unraveling intricate complexities within the atomic realm, particularly concerning the understanding of doubly magic nuclei.
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