長寿命の量子状態が放射性原子核の謎を解く道を指し示す(Long-lived quantum state points the way to solving a mystery in radioactive nuclei)

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2023-08-16 オークリッジ国立研究所(ORNL)

◆エネルギー省のTimothy Gray氏率いる研究チームが行った研究で、原子核の予期せぬ形状変化が示唆されました。この発見は原子核の結びつきや陽子と中性子の相互作用、元素の生成の理解に影響を与える可能性があります。
◆ナトリウム-32核の興奮状態を使用して行った実験で、核の形状進化に関する予想外の結果が得られました。この結果は、原子核の形状とエネルギーが時間とともに変化することを探求する重要な研究です。新たに観測された長寿命の興奮状態は、従来の理論とは異なる可能性を示唆しており、原子核の性質に関する理解を深める上で重要です。

<関連情報>

FRIBで観測されたN=20形状反転島のマイクロ秒異性体 Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB

T. J. Gray et al.
Physical Review Letters  Published 13 June 2023
DOI:https://doi.org/10.1103/PhysRevLett.130.242501

長寿命の量子状態が放射性原子核の謎を解く道を指し示す(Long-lived quantum state points the way to solving a mystery in radioactive nuclei)

ABSTRACT

Excited-state spectroscopy from the first experiment at the Facility for Rare Isotope Beams (FRIB) is reported. A 24(2)−μs isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV γ rays in coincidence with 32Na nuclei. This is the only known microsecond isomer (1  μs≤T1/2<1  ms) in the region. This nucleus is at the heart of the N=20 island of shape inversion and is at the crossroads of the spherical shell-model, deformed shell-model, and ab initio theories. It can be represented as the coupling of a proton hole and neutron particle to 32Mg, 32Mg+π−1+1. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of 32Mg, where the onset of spherical-to-deformed shape inversion begins with a low-lying deformed 2+ state at 885 keV and a low-lying shape-coexisting 0+2 state at 1058 keV. We suggest two possible explanations for the 625-keV isomer in 32Na: a 6− spherical shape isomer that decays by E2 or a 0+ deformed spin isomer that decays by M2. The present results and calculations are most consistent with the latter, indicating that the low-lying states are dominated by deformation.

1700応用理学一般
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