According to the instability of oxygen-28, its neutrons are not arranged properly in the shells. Maria Goeppert Mayer discovered in the late 1940s that certain nuclei—especially those with 2, 8, 20, 28, 50, and 82 protons or neutrons—tend to be more stable than isotopes of similar composition. He used this finding to develop the concept of the nuclear shell, in which electrons are arranged in different energy levels, as are protons and neutrons in atoms.
Similar to noble gases, isotopes have so-called magic numbers of protons, neutrons, or both, and gain stability by having outermost filled shells because it takes a lot of energy to move to the next shell.
But according to recent research, the magical character of some nucleon numbers may fluctuate for nuclei brimming with neutrons. The latest evidence was produced by a team led by scientists at the Tokyo Institute of Technology who created and measured oxygen-28 nuclei for the first time. Although the double magic contains eight protons and 20 neutrons, the nucleus appears to disintegrate quickly and host a defective outer neutron shell during its brief existence.
28To produce and detect O, researchers created a complex experimental setup at the RIKEN Radioactive Isotope Beam Factory in Wako, Japan.
By intensely focusing a beam of neutron-rich calcium nuclei onto a target made of beryllium, all but an extra proton 28They created several types, including fluorine-29, which is identical to O.
Team 29He separated the F and directed it into a pool of liquid hydrogen, which occasionally released protons of one of the incoming isotopes. 28He released it to do. The hardest part was proving that the neutron-rich isotope was actually there. The scientists did this by using sophisticated detectors to find all five of the expected decay products: four neutrons and one extra 24That core.
In the experiment, 28Little evidence has been provided to support the theory that O's supposed double magic state contributes to any stability advantage.
scientists 28It is believed that O has a temporary resonance and rapidly emits two pairs of neutrons. 26It quickly forms O, which is relatively stable but short-lived. 24He believes that He is watching.
Additionally, to support their claims, both 28He also 29Using F measurements, they argue that some of the outermost neutrons of the oxygen nucleus cross the energy gap and flow into another shell, preventing the proper shell closure predicted by theory.
28Measurements need to be confirmed by further research to determine the nuclear structure of O. But the RIKEN results are consistent with previous research showing that magic numbers are not infallible. Although they are slightly heavier than oxygen, isotopes of elements such as neon and magnesium do not appear to have closed shells when bombarded with 20 neutrons. Moreover, 28The final byproduct of the breakdown of O 24It is able to pack its 16 neutrons (a number not thought to be magical) into a closed valence shell. Nuclear physicists will have many opportunities to study other nuclei full of neutrons, thanks to powerful facilities such as RIKEN and the soon-to-be-built Rare Isotope Beam Facility.
Source: Physics Today
📩 17/09/2023 22:25