Lifetimes of low-lying levels in 158Gd

The low-lying structure of the well-deformed nucleus 158Gd has been revisited to elucidate the nature of the low-lying states in 158Gd. 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′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 (ββ) excitation. Systematic comparisons with neighboring Gd isotopes, Hartree–Fock–Bogoliubov, and interacting-boson model predictions suggest that the first excited 0+ state in 158Gd 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 Kπ=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 158Gd’s potential energy surface may support both quadrupole and octupole vibrational modes, in agreement with microscopic calculations [1, 2–3].