Interplay of quasiparticle and vibrational excitations: First observation of isomeric states in 168Dy and 169Dy

G. X. Zhang, H. Watanabe, G. D. Dracoulis, F. G. Kondev, G. J. Lane, P. H. Regan, P. A. Söderström, P. M. Walker, K. Yoshida, H. Kanaoka, Z. Korkulu, P. S. Lee, J. J. Liu, S. Nishimura, J. Wu, A. Yagi, D. S. Ahn, T. Alharbi, H. Baba, F. BrowneA. M. Bruce, M. P. Carpenter, R. J. Carroll, K. Y. Chae, C. J. Chiara, Zs Dombradi, P. Doornenbal, A. Estrade, N. Fukuda, C. Griffin, E. Ideguchi, N. Inabe, T. Isobe, S. Kanaya, I. Kojouharov, T. Kubo, S. Kubono, N. Kurz, I. Kuti, S. Lalkovski, T. Lauritsen, C. S. Lee, E. J. Lee, C. J. Lister, G. Lorusso, G. Lotay, E. A. McCutchan, C. B. Moon, I. Nishizuka, C. R. Nita, A. Odahara, Z. Patel, V. H. Phong, Zs Podolyák, O. J. Roberts, H. Sakurai, H. Schaffner, D. Seweryniak, C. M. Shand, Y. Shimizu, T. Sumikama, H. Suzuki, H. Takeda, S. Terashima, Zs Vajta, J. J. Valiente-Dóbon, Z. Y. Xu, S. Zhu

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The neutron-rich dysprosium isotopes 168Dy102 and 169Dy103 have been investigated using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity uranium beam in conjunction with isotope separation through the BigRIPS separator at RIBF in RIKEN Nishina Center. For 168Dy, a previously unreported isomer with a half-life of 0.57(7) μs has been identified at an excitation energy of 1378 keV, and its presence affirmed independently using γ-γ-γ coincidence data taken with Gammasphere via two-proton transfer from an enriched 170Er target performed at Argonne National Laboratory. This isomer is assigned Jπ=Kπ=(4) based on the measured transition strengths, decay patterns, and the energy systematics for two-quasiparticle states in N=102 isotones. The underlying mechanism of two-quasiparticle excitations in the doubly midshell region is discussed in comparison with the deformed QRPA and multi-quasiparticle calculations. In 169Dy, the B(E2) value for the transition de-exciting the previously unreported Kπ=(1/2) isomeric state at 166 keV to the Kπ=(5/2) ground state is approximately two orders of magnitude larger than the E2 strength for the corresponding isomeric-decay transition in the N=103 isotone 173Yb, suggesting the presence of a significant γ-vibrational admixture with a dominant neutron one-quasiparticle component in the isomeric state.

Original languageEnglish
Article number135036
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - Dec 10 2019
Externally publishedYes


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