Lifetimes of low-lying levels in ^158Gd

Abstract The low-lying structure of the well-deformed nucleus ^158 158 Gd has been revisited to elucidate the nature of the low-lying states in ^158 158 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^ n, n ′ γ) measurements are combined, including γ - γ 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 γ -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 (β β) excitation. Systematic comparisons with neighboring Gd isotopes, Hartree–Fock–Bogoliubov, and interacting-boson model predictions suggest that the first excited 0 ^+ + state in ^158 158 Gd is predicted to be a β -vibration, although it is weakly collective. We also present results for lifetimes and transition probabilities for a number of negative parity states, including K^ =0^-, 1^-, 2^- K π = 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