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

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.

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

Date

2016-08-31

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.

Publisher

Elsevier

Abstract

The level structure of 172 Dy has been investigated for the first time by means of decay spectroscopy following in-flight fission of a 238 U 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 172 Ho 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.