No abstract

The set of parameters for α-nucleus potential is derived by using the data for both the α-decay halflives and the fusion cross-sections around the barrier for reactions α+ 40 Ca, α+ 59 Co, α+ 208 Pb. The α-decay half-lives are obtained in the framework of a cluster model using the WKB approximation. The evaluated α-decay half-lives and the fusion cross-sections agreed well with the data. Fusion reactions between α-particle and heavy nuclei can be used for both the formation of very heavy nuclei and spectroscopic studies of the formed compound nuclei.

In order to study the nucleus-nucleus interaction in Pb-based cold fusion, we have measured excitation functions for quasielastic scattering of 48Ti, 54Cr, 56Fe, 64Ni, and 70Zn projectiles on a 208Pb target at backward angles. The barrier distributions were derived from the first derivative of measured quasielastic scattering cross sections relative to the Rutherford scattering cross section. The centroids of the barrier distributions show a deviation from several predicted barrier heights toward the low energy side. The shape of the barrier distributions is well reproduced by the results of a coupled-channel calculation taking account of the coupling effects of two phonon excitations of the quadrupole vibration for the projectiles and of the octupole vibration for the 208Pb target.

Fission cross sections and fission fragment mass distributions were measured in the reactions of 40 Ca + 238 U and 48 Ca + 238 U at energies around the Coulomb barrier. Fusion probabilities were calculated based on the fluctuation dissipation model. The measured mass distributions for both reactions showed an asymmetric shape at low incident energies, whereas the distribution changed to a flat shape at higher energies. The variation of the mass distribution is explained by a change of the ratio between fusion and quasifission with nuclear orientation. The calculation reproduced the mass distributions and their energy dependence. The trajectories for fusion-fission were used to determine the fusion probability. Fusion probabilities for both reactions are identical as function of the center-of-mass energy (E c.m. ), but they differ when plotted as function of the excitation energy (E * ). Evaporation residue cross sections were calculated for the reaction 48 Ca + 238 U using a statistical model and the obtained fusion cross sections as input values. The results are compared to experimental data.