No abstract

The influence of the Landau-Zener effect on the fine structure of the cluster decay phenomenon is evidenced. Estimations of hindrance factors are reported for the 14 C emission from 223 Ra. The half-lives are calculated considering the cluster decay as a superasymmetric fission process appealing to the Wentzel-Kramers-Brillouin penetrabilities. The excitation of the last unpaired nucleon is considered to be due mainly to the Landau-Zener promotion mechanism. The deformation energy is computed in the framework Yukawa-plus-exponential model extended for binary systems with different charge densities and adding the specialization energy of the unpaired nucleon. The Werner-Wheeler approximation is used to compute the effective mass. Assuming molecular states during the disintegration, the superasymmetric two-center shell model is used to obtain the level scheme of the cluster decay. ͓S0556-2813͑98͒06205-0͔

A new isomer in the neutron-rich isotope 32 Al has been identified among the fragmentation products of beams of 75A MeV 36 S and 61A MeV 40 Ar using the LISE spectrometer at GANIL. The population of an isomeric state was inferred from the detection of ␥ radiation following the decay of an implanted 32 Al fragment. A half-life for 32 Al m of 200͑20͒ ns was measured, and an excitation energy of 956 keV deduced from the observed ␥-ray cascade. Shell model calculations provide a candidate for the isomer, having J ϭ4 ϩ . However, this association reveals a rare inversion of low-energy levels by the Wildenthal's ''universal'' sd-shell ͑USD͒ interaction, extending to the Nϭ19, Zϭ13 range of USD anomalies ͑previously identified for Nϭ20, Zϭ11,12) linked to the vanishing of the Nϭ20 shell gap.

A two-center parametrization with smoothed neck is used to describe the shapes during the fission process of 234 U in a wide range of mass asymmetry (cold fission with 100 Zr fragment, 28 Mg radioactivity and α-decay). The optimum fission path has been found by minimizing the action integral. The neck influence is stronger for lower mass asymmetry.

The influence of the Landau-Zener effect on the fine structure of cluster decay phenomenon is emphasized. Estimations of hindrance factors are reported for the 14 C emission from 223 Ra. The half-lives are computed considering the cluster decay as a superasymmetric fission process. The level scheme is evaluated with the superasymmetric two-center shell model.