Long-lived K isomer and enhanced γ vibration in the neutron-rich nucleus 172Dy: Collectivity beyond double midshell

• Published in: Physics letters. B 2016-09, Vol.760 (C), p.641-646
• Main Authors: Watanabe, H., Zhang, G.X., Yoshida, K., Walker, P.M., Liu, J.J., Wu, J., Regan, P.H., Söderström, P.-A., Kanaoka, H., Korkulu, Z., Lee, P.S., Nishimura, S., Yagi, A., Ahn, D.S., Alharbi, T., Baba, H., Browne, F., Bruce, A.M., Carroll, R.J., Chae, K.Y., Dombradi, Zs, Doornenbal, P., Estrade, A., Fukuda, N., Griffin, C., Ideguchi, E., Inabe, N., Isobe, T., Kanaya, S., Kojouharov, I., Kondev, F.G., Kubo, T., Kubono, S., Kurz, N., Kuti, I., Lalkovski, S., Lane, G.J., Lee, C.S., Lee, E.J., Lorusso, G., Lotay, G., Moon, C.-B., Nishizuka, I., Nita, C.R., Odahara, A., Patel, Z., Phong, V.H., Podolyák, Zs, Roberts, O.J., Sakurai, H., Schaffner, H., Shand, C.M., Shimizu, Y., Sumikama, T., Suzuki, H., Takeda, H., Terashima, S., Vajta, Zs, Valiente-Dóbon, J.J., Xu, Z.Y.
• Format: Article
• Language: English
• Subjects: 172Dy; Axial symmetry; Decay spectroscopy; K isomer; γ vibration
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2016.07.057

The level structure of 172Dy has been investigated for the first time by means of decay spectroscopy following in-flight fission of a 238U beam. A long-lived isomeric state with T1/2=0.71(5) s and Kπ=8− has been identified at 1278 keV, which decays to the ground-state and γ-vibrational bands through hindered electromagnetic transitions, as well as to the daughter nucleus 172Ho via allowed β decays. The robust nature of the Kπ=8− isomer and the ground-state rotational band reveals an axially-symmetric structure for this nucleus. Meanwhile, the γ-vibrational levels have been identified at unusually low excitation energy compared to the neighboring well-deformed nuclei, indicating the significance of the microscopic effect on the non-axial collectivity in this doubly mid-shell region. The underlying mechanism of enhanced γ vibration is discussed in comparison with the deformed Quasiparticle Random-Phase Approximation based on a Skyrme energy-density functional.