Eur. Phys. J. A (2026) 62: 17
https://doi.org/10.1140/epja/s10050-025-01776-2

Regular Article - Experimental Physics

Evidence for an isomeric $\pi {\frac{1}{2}}^{+}[411]$ state in $_{}^{183}$Ta

¹ School of Architecture, Technology and Engineering, University of Brighton, BN2 4AT, Brighton, UK
² School of Mathematics and Physics, University of Surrey, GU2 7XH, Guildford, UK
³ Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, 77125, Bucharest-Magurele, Romania
⁴ RIKEN Nishina Center, 2-1 Hirosawa, 351-0198, Wako, Saitama, Japan
⁵ School of Physics, Beihang University, Haidian District, 100191, Beijing, China
⁶ School of Physics and Astronomy, University of Edinburgh, EH8 9YL, Edinburgh, UK
⁷ Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
⁸ Wako Nuclear Science Center, Institute of Particle and Nuclear Studies, KEK, 351-0198, Wako, Japan
⁹ Physics Division, Argonne National Laboratory, 60439, Lemont, IL, USA
¹⁰ Department of Nuclear Physics, RSPhys, Australian National University, 2601, Canberra, ACT, Australia
¹¹ GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
¹² School of Nuclear Science and Technology, University of Chinese Academy of Sciences, 100049, Beijing, China
¹³ Center for Exotic Nuclear Studies, Institute for Basic Science, 34126, Daejeon, Republic of Korea
¹⁴ Institut für Kernphysik, Universität zu Köln, Zülpicher Str. 77, 50937, Köln, Germany

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Received: 3 November 2025
Accepted: 17 December 2025
Published online: 23 January 2026

Abstract

We report on the identification of a new isomeric state in $_{}^{183}$Ta populated via the ground-state $\beta$-decay of $_{}^{183}$Hf. The experiment was performed at the KISS setup at RIKEN, where neutron-rich hafnium isotopes were produced via multi-nucleon transfer (MNT) reactions, followed by laser ionization of hafnium atoms, mass separation, and detection using an electron-gamma coincidence system. Isomeric spectroscopy was carried out by gating on different electron-gamma time correlations. A 459.1 keV $\gamma$-ray transition was identified in delayed spectra, and a half-life of ${41}_{-4}^{+6}\mathrm{\mu }s$ was extracted through time-distribution fitting. The 459.1 keV state in $_{}^{183}$Ta is known from previous work and has been assigned a Nilsson orbital configuration of $5/2^{+}[402]$, while a proposed new isomeric state above it is interpreted as a $1/2^{+}[411]$ configuration that decays to $5/2^{+}[402]$ via a low-energy, unobserved E2 transition. This is consistent with the systematic trends in neighbouring odd-A nuclei and transition rate calculations.