Abstract
Recoil-distance lifetime measurements of levels in have been carried out using the (,) reaction at 54 MeV on natural La targets evaporated on gold. The data were analyzed using a computer code which treats complex cascade feeding in a rigorous formalism. The following lifetimes have been measured (energy is in keV and spin parity are in parentheses): 1811.5(), ps; 2600.3(), 16±6 ps; 2737.1(), 16.4±6.0 ps; 2797.6(), ns; 3354.5(), ps; 3783.5(), ps; 4091.2(), ps; 4628.8(), ps. Lifetimes have also been measured for the 747.2(), 1381.2(), and 4461.4() states but with considerably less precision. The results support the interpretation of the yrast odd-spin negative parity states ( through ) as being described by an octupole phonon coupled to the through yrast even-spin, positive-parity "ground-state band" states. The results for the through states are compared to calculations of the interacting boson approximation model and cluster-vibrator model. Both models are not inconsistent with the observed transition probabilities up to the → transition, but fail to reproduce that for the → transition. Our results support spin-parity arrangements of and for the 4461 and 4629 keV states, respectively.
NUCLEAR REACTIONS (,), MeV; measured recoil-distance Doppler shift. levels, deduced lifetimes, reduced transition probabilities. Ge(Li) detectors, plunger.
- Received 29 October 1981
DOI:https://doi.org/10.1103/PhysRevC.25.3000
©1982 American Physical Society