New Magic Number 34 Observed by Direct Mass Measurements

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  • 核質量でみる新魔法数34
  • カクシツリョウ デ ミル シン マホウスウ 34

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Abstract

<p>The atomic nucleus has shell structures for both protons and neutrons with significant energy gaps occurring at particular occupation numbers. These numbers are called “magic numbers”, in analogy to the shell structure of noble gases in atomic physics. The magic numbers, which are 2, 8, 20, 28, 50, 82 and 126 protons or neutrons, suggested by Mayer and Jensen are well established in nuclei on or near the valley of stability. However, far from the valley of stability, these magic numbers can change in nuclei with a large excess of neutrons. The previous researches make it evident that the traditional shell closures at 8, 20, and 28 disappear, and that new ones at 16 and 32 are known to emerge. Here, we report on a study of the emergence of new magic number 34. The magic number 34 was predicted by a nuclear theory that well reproduces an occurrence of the magic number 16. The first experimental indication was reported by in-beam γ-ray spectroscopy of 54Ca. To identify whether magic number 34 emerges, we performed the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number of 34 at the RIKEN RI Beam Factory by using the magnetic-rigidity time-of-flight technique. The atomic mass excesses of 55-57Ca were determined for the first time and provide an energy difference in Ca isotopes between neutron 2p1/2 and 1f5/2 orbitals. The experimental results identify the experimental signature of a sizable energy gap in 54Ca.</p>

Journal

  • Butsuri

    Butsuri 74 (12), 850-855, 2019-12-05

    The Physical Society of Japan

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