Eur. Phys. J. A (2023) 59: 199
https://doi.org/10.1140/epja/s10050-023-01103-7

Regular Article - Experimental Physics

Interpretation of metastable states in the $N>70$ Zr region

¹ School of Computing, Engineering and Mathematics, University of Brighton, BN2 4GJ, Brighton, UK
² RIKEN Nishina Center, 2-1 Hirosawa, 351-0198, Wako, Saitama, Japan
³ Department of Physics, Tohoku University, Aoba, 980-8578, Sendai, Miyagi, Japan
⁴ Department of Technical Physics, Peking University, 100871, Beijing, China
⁵ Department of Physics, University of Surrey, GU2 7XH, Guildford, UK
⁶ National Physical Laboratory, TW11 0LW, Teddington, Middlesex, UK
⁷ Extreme Light Infrastructure-Nuclear Physics (ELI-NP)/Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), Str. Reactorului 30, 077125, Bucharest-Măgurele, Romania
⁸ IRCNPC, School of Physics and Nuclear Energy Engineering, Beihang University, 100191, Beijing, China
⁹ Department of Physics, Osaka University, 560-0043, Toyonaka, Osaka, Japan
¹⁰ Department of Physics, University of York, Heslington, YO10 5DD, York, UK
¹¹ Department of Physics, Peking University, 100871, Beijing, China
¹² Department of Physics, University of Tokyo, 113-0033, Hongo, Bunkyo-ku, Tokyo, Japan
¹³ Department of Physics, University of Hong Kong, Pokfulam Road, Pokfulam, Hong Kong
¹⁴ IPHC, CNRS/IN2P3, Université de Strasbourg, 67037, Strasbourg, France
¹⁵ LPSC, Université Grenoble-Alpes, CNRS/IN2P3, 38026, Grenoble Cedex, France
¹⁶ ILL, 38042, Grenoble Cedex, France
¹⁷ Research Center for Nuclear Physics, Osaka University, 10-1 Mihogaoka, 567-0047, Ibaraki, Japan
¹⁸ GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
¹⁹ Department of Physics, University of Sofia, 1164, Sofia, Bulgaria
²⁰ Université Paris-Saclay, IJCLab, 91405, Orsay, France
²¹ CSNSM, CNRS/IN2P3, Université Paris-Sud, Orsay Campus, 91405, Orsay, France
²² Department of Physics, Kyushu University, 819-0395, Fukuoka, Japan
²³ Research Center for Nuclear Physics (RCNP), Osaka University, 567-0047, Ibaraki, Osaka, Japan
²⁴ Departamento de Física Teórica, Universidad Autónoma de Madrid, 28049, Madrid, Spain
²⁵ Instituto de Estructura de la Materia, CSIC, 28006, Madrid, Spain
²⁶ A. W. Wright Nuclear Structure Laboratory, Yale University, 06520, New Haven, CT, USA
²⁷ Institut für Kernphysik, Technische Universität Darmstadt, 64289, Darmstadt, Germany
²⁸ INFN Sezione di Milano, 20133, Milan, Italy

^a frank.browne@cern.ch

Received: 14 December 2022
Accepted: 24 July 2023
Published online: 8 September 2023

Abstract

Isomeric states were observed in nuclei produced in an experiment at the RIKEN Nishina Center Radioactive Isotope Beam Factory following the in-flight fission of a 345 MeV/nucleon ${}^{238}$U beam. Isomers reported in nuclei spanning a predicted prolate-oblate shape change boundary, ${}^{111}$Zr ($E=283.1$keV; $\tau =0.326(63)$ $\mathrm{\mu }$s), ${}^{112}$Nb ($E=44.2$ keV; $\tau =0.094(26)$ $\mathrm{\mu }$s), ${}^{113}$Nb ($E=135.4$ keV; $\tau =0.846(80)$ $\mathrm{\mu }$s), and ${}^{115}$Mo ($E=198.6$ keV; $\tau =63(4)$ $\mathrm{\mu }$s), are compared to potential-energy surface calculations which gave a selection of low-lying configurations for each nucleus. Tentative assignments of ground and excited states were made based on energy similarities to the calculations, reduced transition probabilities of the decays, and constraints of transition multipolarities from $\gamma$-ray coincidence measurements. These assignments are suggestive of significant deformation being persistent for $N>70$ in this region. In addition, isomers in ${}^{108}$Nb, ${}^{109}$Nb, ${}^{113}$Tc, ${}^{117}$Ru, ${}^{119}$Ru, ${}^{120}$Rh, and ${}^{122}$Rh, not spanning the prolate-oblate transition discussed, are presented.