Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB
Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB
Excited-state spectroscopy from the first Facility for Rare Isotope Beams (FRIB) experiment is reported. A 24(2)-$\mu$s isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV $\gamma$ rays in coincidence with $^{32}\textrm{Na}$ nuclei. This is the only known microsecond isomer ($1{\text{ }\mu\text{s}}\leq T_{1/2} < 1\text{ ms}$) in the region. This nucleus is at the heart of the $N=20$ island of shape inversion and is at the crossroads of 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 $^{32}\textrm{Mg}$, $^{32}\textrm{Mg}+\pi^{-1} + \nu^{+1}$. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of $^{32}\textrm{Mg}$, 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 $^{32}$Na: 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.
B. C. Rasco、Z. Xu、T. Gaballah、S. L. Tabor、L. Schaedig、A. O. Macchiavelli、C. M. Campbell、B. P. Crider、C. Porzio、J. Chan、T. Miyagi、T. J. Ruland、A. Laminack、M. J. Mogannam、S. Neupane、J. Dopfer、M. P. Carpenter、J. Heideman、T. L. Tang、S. N. Liddick、A. Nowicki、D. Seweryniak、J. L. Wood、J. Christie、E. K. Ronning、M. Madurga、R. Jain、J. G. Duarte、V. Tripathi、S. Bhattacharya、J. D. Holt、R. Mahajan、H. Huegen、W. -J. Ong、R. S. Lubna、A. Chester、P. Fallon、M. Singh、T. T. King、C. Benetti、A. Frotscher、E. Rubino、J. M. Allmond、A. A. Doetsch、B. R. Clark、F. G. Kondev、N. Kitamura、I. Cox、K. Kolos、J. T. Harke、T. H. Ogunbeku、A. Andalib、T. Wheeler、J. A. Winger、K. Siegl、C. Morse、A. Poves、B. Longfellow、A. E. Stuchbery、S. Luitel、C. J. Prokop、T. J. Gray、E. Argo、R. Grzywacz、H. L. Crawford、K. P. Rykaczewski
10.1103/PhysRevLett.130.242501
原子能技术基础理论物理学
B. C. Rasco,Z. Xu,T. Gaballah,S. L. Tabor,L. Schaedig,A. O. Macchiavelli,C. M. Campbell,B. P. Crider,C. Porzio,J. Chan,T. Miyagi,T. J. Ruland,A. Laminack,M. J. Mogannam,S. Neupane,J. Dopfer,M. P. Carpenter,J. Heideman,T. L. Tang,S. N. Liddick,A. Nowicki,D. Seweryniak,J. L. Wood,J. Christie,E. K. Ronning,M. Madurga,R. Jain,J. G. Duarte,V. Tripathi,S. Bhattacharya,J. D. Holt,R. Mahajan,H. Huegen,W. -J. Ong,R. S. Lubna,A. Chester,P. Fallon,M. Singh,T. T. King,C. Benetti,A. Frotscher,E. Rubino,J. M. Allmond,A. A. Doetsch,B. R. Clark,F. G. Kondev,N. Kitamura,I. Cox,K. Kolos,J. T. Harke,T. H. Ogunbeku,A. Andalib,T. Wheeler,J. A. Winger,K. Siegl,C. Morse,A. Poves,B. Longfellow,A. E. Stuchbery,S. Luitel,C. J. Prokop,T. J. Gray,E. Argo,R. Grzywacz,H. L. Crawford,K. P. Rykaczewski.Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB[EB/OL].(2023-02-22)[2025-08-03].https://arxiv.org/abs/2302.11607.点此复制
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