Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB

T. J. Gray, J. M. Allmond, Z. Xu, T. T. King, R. S. Lubna, H. L. Crawford, V. Tripathi, B. P. Crider, R. Grzywacz, S. N. Liddick, A. O. Macchiavelli, T. Miyagi, A. Poves, A. Andalib, E. Argo, C. Benetti, S. Bhattacharya, C. M. Campbell, M. P. Carpenter, J. ChanA. Chester, J. Christie, B. R. Clark, I. Cox, A. A. Doetsch, J. Dopfer, J. G. Duarte, P. Fallon, A. Frotscher, T. Gaballah, J. T. Harke, J. Heideman, H. Huegen, J. D. Holt, R. Jain, N. Kitamura, K. Kolos, F. G. Kondev, A. Laminack, B. Longfellow, S. Luitel, M. Madurga, R. Mahajan, M. J. Mogannam, C. Morse, S. Neupane, A. Nowicki, T. H. Ogunbeku, W. J. Ong, C. Porzio, C. J. Prokop, B. C. Rasco, E. K. Ronning, E. Rubino, T. J. Ruland, K. P. Rykaczewski, L. Schaedig, D. Seweryniak, K. Siegl, M. Singh, A. E. Stuchbery, S. L. Tabor, T. L. Tang, T. Wheeler, J. A. Winger, J. L. Wood

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    10 Citations (Scopus)

    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 Na32 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 Mg32, Mg32+π-1+ν+1. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of Mg32, 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 02+ state at 1058 keV. We suggest two possible explanations for the 625-keV isomer in Na32: 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.

    Original languageEnglish
    Article number242501
    JournalPhysical Review Letters
    Volume130
    Issue number24
    DOIs
    Publication statusPublished - 16 Jun 2023

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