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

Autor: Gray, T. J., Allmond, J. M., Xu, Z., King, T. T., Lubna, R. S., Crawford, H. L., Tripathi, V., Crider, B. P., Grzywacz, R., Liddick, S. N., Macchiavelli, A. O., Miyagi, T., Poves, A., Andalib, A., Argo, E., Benetti, C., Bhattacharya, S., Campbell, C. M., Carpenter, M. P., Chan, J., Chester, A., Christie, J., Clark, B. R., Cox, I., Doetsch, A. A., Dopfer, J., Duarte, J. G., Fallon, P., Frotscher, A., Gaballah, T., Harke, J. T., Heideman, J., Huegen, H., Holt, J. D., Jain, R., Kitamura, N., Kolos, K., Kondev, F. G., Laminack, A., Longfellow, B., Luitel, S., Madurga, M., Mahajan, R., Mogannam, M. J., Morse, C., Neupane, S., Nowicki, A., Ogunbeku, T. H., Ong, W. -J., Porzio, C., Prokop, C. J., Rasco, B. C., Ronning, E. K., Rubino, E., Ruland, T. J., Rykaczewski, K. P., Schaedig, L., Seweryniak, D., Siegl, K., Singh, M., Stuchbery, A. E., Tabor, S. L., Tang, T. L., Wheeler, T., Winger, J. A., Wood, J. L.
Rok vydání: 2023
Předmět:
Druh dokumentu: Working Paper
DOI: 10.1103/PhysRevLett.130.242501
Popis: 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.
Comment: 7 pages, 5 figures, accepted by Physical Review Letters
Databáze: arXiv
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