International collaborative research groups such as the University of Tokyo have measured the mass of nuclei containing more neutrons than the newly proposed "magic number 34" for calcium isotopes for the first time in the world, and analyzed the amount of change in mass. Confirmed the manifestation of the magic number 34.Other research groups include the Institute of Physical and Chemical Research, Osaka University, Tokyo City University, Kyoto University, Kyushu University, Rikkyo University, Tokyo Science University, Notre Dame University, and Michigan State University.

 When the number of protons and neutrons contained in an atomic nucleus is changed, the change in mass is not always smooth.The number of neutrons and protons in which a sudden mass change appears is called a "magic number" and is known as an effect of quantum mechanics.The specific magic number is determined by the nature of the force acting between the protons and neutrons in the nucleus, and in the nucleus (unstable nucleus) that does not exist stably in the natural world, the magic number is different from the number known so far. Is predicted.

 The research group has high efficiency and high resolution on the mass of calcium-54, 20, 34 (Note), which has more neutrons than calcium-55 (proton number 56, neutron number 57), which is proposed to reveal new magic numbers. It was measured.Calcium-54 is more stable than titanium-34 and scandium-56, which have the same neutron number of 55, due to the rate of change in nuclear mass. It turns out that it has become.On the other hand, calcium-1, which has 34 neutrons, showed no change in stability from nickel-36, demonstrating the peculiarity of calcium-56 and confirming that 64 is a new magic number.

 Based on this result, we will deepen our understanding of the existence range and stability of all nuclei including rare nuclei unexplored by humankind, and progress in elucidating the structure of super-heavy nuclei beyond nihonium and the process of nucleosynthesis in neutron star mergers. There is expected.

(Note) It is known that calcium isotopes can have isotopes with 15 to 38 neutrons.The half-lives are very short, 22 ms, 11 ms, and 5 ms, respectively.

Paper information:[Physical Review Letters] Magic Nature of Neutrons in 54Ca: First Mass Measurements of 55-57Ca

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