Three-quasiparticle isomers in odd-even <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi>Pm</mi><mprescripts></mprescripts><none></none><mrow><mn>159</mn><mo>,</mo><mn>161</mn></mrow></mmultiscripts></math>: Calling for modified spin-orbit interaction for the neutron-rich region

R. Yokoyama; E. Ideguchi; G. S. Simpson; Mn. Tanaka; Yang Sun; Cui-Juan Lv; Yan-Xin Liu; Long-Jun Wang; S. Nishimura; P. Doornenbal; G. Lorusso; P.-A. Söderström; T. Sumikama; J. Wu; Z. Y. Xu; N. Aoi; H. Baba; F. L. Bello Garrote; G. Benzoni; F. Browne; R. Daido; Y. Fang; N. Fukuda; A. Gottardo; G. Gey; S. Go; S. Inabe; T. Isobe; D. Kameda; K. Kobayashi; M. Kobayashi; I. Kojouharov; T. Komatsubara; T. Kubo; N. Kurz; I. Kuti; Z. Li; M. Matsushita; S. Michimasa; C. B. Moon; H. Nishibata; I. Nishizuka; A. Odahara; Z. Patel; S. Rice; E. Sahin; H. Sakurai; H. Schaffner; L. Sinclair; H. Suzuki; H. Takeda; J. Taprogge; Zs. Vajta; H. Watanabe; A. Yagi

doi:10.1103/PhysRevC.104.L021303

Letter

Three-quasiparticle isomers in odd-even ${}^{159, 161}{Pm}$ : Calling for modified spin-orbit interaction for the neutron-rich region

R. Yokoyama ^1,2,*, E. Ideguchi³, G. S. Simpson⁴, Mn. Tanaka³, Yang Sun^5,†, Cui-Juan Lv⁵, Yan-Xin Liu⁶, Long-Jun Wang⁷, S. Nishimura⁸ et al.

P. Doornenbal⁸, G. Lorusso⁸, P.-A. Söderström⁸, T. Sumikama⁹, J. Wu^10,8, Z. Y. Xu¹¹, N. Aoi³, H. Baba⁸, F. L. Bello Garrote¹², G. Benzoni¹³, F. Browne^14,8, R. Daido¹⁵, Y. Fang¹⁵, N. Fukuda⁸, A. Gottardo^16,17, G. Gey^18,8, S. Go², S. Inabe⁸, T. Isobe⁸, D. Kameda⁸, K. Kobayashi¹⁹, M. Kobayashi², I. Kojouharov²⁰, T. Komatsubara^21,22, T. Kubo⁸, N. Kurz²⁰, I. Kuti²³, Z. Li¹⁰, M. Matsushita², S. Michimasa², C. B. Moon²⁴, H. Nishibata¹⁵, I. Nishizuka⁹, A. Odahara¹⁵, Z. Patel^8,25, S. Rice^8,25, E. Sahin¹², H. Sakurai^8,11, H. Schaffner^26,8, L. Sinclair^26,8, H. Suzuki⁸, H. Takeda⁸, J. Taprogge^27,28, Zs. Vajta²³, H. Watanabe²⁹, and A. Yagi¹⁵

¹Department of Physics and Astronomy, University of Tennessee, Koxville, Tennessee 37996, USA
²Center for Nuclear Study, the University of Tokyo, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
³Research Center for Nuclear Physics, Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
⁴LPSC, 53 Rue des Martyrs, F-38026 Grenoble Cedex, France
⁵School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
⁶School of Science, Huzhou University, Huzhou 313000, China
⁷School of Physical Science and Technology, Southwest University, Chongqing 400715, China
⁸RIKEN, Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁹Department of Physics, Tohoku University, Aramaki-aza-aoba, Aoba, Sendai, Miyagi 980-8578, Japan
¹⁰Department of Physics, Peking University, Beijing 100871, China
¹¹Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹²Department of Physics, University of Oslo, Oslo NO-0316, Norway
¹³INFN, Sezione di Milano, I-20133 Milano, Italy
¹⁴School of Computing, Engineering and Mathematics, University of Brighton, Brighton BN2 4GJ, United Kingdom
¹⁵Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
¹⁶Dipartimento di Fisica dellUniversità degli Studi di Padova, I-35131 Padova, Italy
¹⁷INFN, Laboratori Nazionali di Legnaro, Legnaro I-35020, Italy
¹⁸Institut Laue-Langevin, B.P. 156, F-38042 Grenoble Cedex 9, France
¹⁹Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
²⁰GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany
²¹Research Facility Center for Pure and Applied Science, University of Tsukuba, Ibaraki 305-8577, Japan
²²Rare Isotope Science Project, Institute for Basic Science, Daejeon 305-811, Korea
²³MTA Atomki, P.O. Box 51, Debrecen H-4001, Hungary
²⁴Hoseo University, Asan, Chungnam 336-795, Korea
²⁵Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom
²⁶Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom
²⁷Instituto de Estructura de la Materia, CSIC, E-28006 Madrid, Spain
²⁸Departamento de Física Teórica, Universidad Autónoma de Madrid, Madrid, Spain
²⁹International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191, China

^*ryokoyam@utk.edu
^†sunyang@sjtu.edu.cn

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Phys. Rev. C 104, L021303 – Published 24 August, 2021

DOI: https://doi.org/10.1103/PhysRevC.104.L021303

Abstract

Neutron-rich Pm ( $Z = 61$ ) isotopes were studied by delayed $γ$ -ray spectroscopy at RIBF, RIKEN Nishina Center using the in-flight fission of a 345 MeV/nucleon ${}^{238}U$ beam. A cluster-type Ge detector array, EURICA, was used to measure the delayed $γ$ rays from stopped ions. Isomeric $γ$ decays were observed in ${}^{159}{Pm}$ and ${}^{161}{Pm}$ with half-lives of 4.97(12) $μ s$ and 0.79(4) $μ s$ , respectively. Level schemes for ${}^{159}{Pm}$ and ${}^{161}{Pm}$ were constructed in this study. The isomeric states of ${}^{159}{Pm}$ and ${}^{161}{Pm}$ could be interpreted as two quasiparticle excitations of neutrons with the configurations of $ν (7 / 2 [633] \otimes 5 / 2 [523])$ and $ν (7 / 2 [633] \otimes 1 / 2 [521])$ , respectively. They are analogous to the isomers that have been observed systematically in other even-mass $N = 98$ and $N = 100$ isotones in this region. A projected shell model calculation was performed and it reproduced the order of three-quasiparticle states only if new Nilsson parameters with an $N$ -dependent spin-orbit interaction were used. This work demonstrates that the strength of spin-orbit interactions in standard Nilsson parameters needs to be modified to study the properties of neutron-rich rare-earth nuclei around $A = 165$ , and provides new evidence supporting the existence of the deformed $N = 98$ subshell gap in odd-mass nuclei for the first time.

Physical Review C

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Three-quasiparticle isomers in odd-even ${}^{159, 161}{Pm}$ : Calling for modified spin-orbit interaction for the neutron-rich region

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Three-quasiparticle isomers in odd-even Pm159,161: Calling for modified spin-orbit interaction for the neutron-rich region

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Three-quasiparticle isomers in odd-even ${}^{159, 161}{Pm}$ : Calling for modified spin-orbit interaction for the neutron-rich region