Two-quasiparticle K-isomers and pairing strengths in the neutron-rich isotopes Er and Er |
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Authors: | G.D. Dracoulis G.J. Lane F.G. Kondev A.P. Byrne R.O. Hughes P. Nieminen H. Watanabe M.P. Carpenter R.V.F. Janssens T. Lauritsen D. Seweryniak S. Zhu P. Chowdhury F.R. Xu |
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Affiliation: | 1. Department of Nuclear Physics, R.S.Phys.S.E., Australian National University, Canberra, ACT, Australia 0200;2. Nuclear Engineering Division, Argonne National Laboratory, Argonne IL, USA;3. Department of Physics, The Faculties, Australian National University, Canberra, ACT, Australia 0200;4. Physics Division, Argonne National Laboratory, Argonne, IL, USA;5. Department of Physics, University of Massachusetts, Lowell, MA 01854, USA;6. School of Physics, Peking University, Beijing 100871, China |
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Abstract: | Isomeric two-quasiparticle states have been identified in the neutron-rich isotopes 172Er and 174Er using multi-nucleon transfer reactions with 136Xe beams incident on various targets, and γ -ray spectroscopy with Gammasphere. A candidate for the Kπ=6+ two-quasineutron state in 172Er is found at 1500 keV. In 174Er, a nuclide whose level scheme was previously unknown, a long-lived isomer is identified at 1112 keV decaying via an inhibited E1 transition and revealing the yrast sequence of 174Er. This isomer is proposed to be a Kπ=8− two-quasineutron state, defining a sequence in the N=106 isotones extending from the well-deformed neutron-rich isotope 174Er to the neutron-deficient isotope 188Pb, where the presence of the isomer signifies a prolate minimum in an otherwise spherical well. Configuration-constrained potential-energy surface calculations are used to predict the excitation energies of the 6+ and 8− intrinsic states and as a basis for extracting the pairing force strength, Gn, in the N=104 and N=106 isotones. |
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Keywords: | 21.10.Re 21.10.Tg 23.20.Lv 27.70.+q |
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