Eur. Phys. J. A (2026) 62: 20
https://doi.org/10.1140/epja/s10050-026-01784-w

Regular Article - Experimental Physics

Lifetimes of low-lying levels in $_{}^{158}$Gd

¹ Department of Physics, North Carolina Agricultural and Technical State University, 27411, Greensboro, NC, USA
² Department of Physics, University of Wisconsin–La Crosse, 54601, La Crosse, WI, USA
³ Department of Physics and Astronomy, University of Notre Dame, 46556, Notre Dame, IN, USA
⁴ Universität zu Köln, 50937, Köln, Germany
⁵ Department of Physics, Yale University, 06520, New Haven, CT, USA
⁶ Department of Chemistry, University of Kentucky, 40506, Lexington, Kentucky, USA

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Received: 16 October 2025
Accepted: 1 January 2026
Published online: 30 January 2026

Abstract

The low-lying structure of the well-deformed nucleus $_{}^{158}$Gd has been revisited to elucidate the nature of the low-lying states in $_{}^{158}$Gd. Earlier (p, t) studies identified numerous 0$_{}^{+}$ states below 4.3 MeV, prompting questions about whether these states correspond to collective vibrations or shape coexistence. New and previously reported ($n,n^{\prime }\gamma$) measurements are combined, including $\gamma$-$\gamma$ coincidences, excitation functions, and angular distributions, to extract lifetimes and transition probabilities for 44 excited states up to 2.7 MeV, including 32 previously unmeasured levels. Our results confirm or revise $\gamma$-ray placements and provide detailed transition strengths, revealing both weakly collective and strongly enhanced B(E2) and B(E1) transition probabilities. In particular, a tentative 0$_{}^{+}$ state at 2437.8 keV exhibits a strong interband B(E2) transition, which may be a candidate for a possible two-phonon ($\beta \beta$) excitation. Systematic comparisons with neighboring Gd isotopes, Hartree–Fock–Bogoliubov, and interacting-boson model predictions suggest that the first excited 0$_{}^{+}$ state in $_{}^{158}$Gd is predicted to be a $\beta$-vibration, although it is weakly collective.

We also present results for lifetimes and transition probabilities for a number of negative parity states, including ${\text{K}}^{\pi }=0^{-},1^{-},2^{-}$ sequences, perhaps providing insight into octupole collectivity and the interplay between quadrupole and octupole vibrations in deformed nuclei. The systematic presence of low-lying negative-parity bands and their interband transition strengths suggest that $_{}^{158}$Gd’s potential energy surface may support both quadrupole and octupole vibrational modes, in agreement with microscopic calculations [1, 2–3].