Level densities and γ\gamma-strength functions in 148,149^{148,149}Sm

The level densities and $\gamma$-strength functions of the weakly deformed $^{148}$Sm and $^{149}$Sm nuclei have been extracted. The temperature versus excitation energy curve, derived within the framework of the micro canonical ensemble, shows structures, which we associate with the break up of Cooper pairs. The nuclear heat capacity is deduced within the framework of both the micro canonical and the canonical ensemble. We observe negative heat capacity in the micro canonical ensemble whereas the canonical heat capacity exhibits an S-shape as function of temperature, both signals of a phase transition. The structures in the $\gamma$-strength functions are discussed in terms of the pygmy resonance and the scissors mode built on exited states. The samarium results are compared with data for the well deformed $^{161,162}$Dy, $^{166,167}$Er and $^{171,172}$Yb isotopes and with data from (n,$\gamma$)-experiments and giant dipole resonance studies.Comment: 12 figure

Synthesis of superheavy nuclei in the reactions of \chem{^{244}Pu} and \chem{^{248}Cm} with \chem{^{48}Ca}

This paper presents results of the experiments aimed at producing long-lived superheavy elements located near the spherical-shell closures with $Z \geqslant 114$ and $N \geqslant 172$ in the \chem{^{244}Pu} + \chem{^{48}Ca} and \chem{^{248}Cm} + \chem{^{48}Ca} reactions. The large measured $\alpha$-particle energies of the newly observed nuclei, together with the long decay times and spontaneous fission terminating the chains, offer evidence of the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive $\alpha$-decays originating from the parent nuclides $^{{288}{,}{289}}$114 and $^{292}$116, produced in the $3n$ and $4n$ evaporation channels with cross-sections of about a picobarn. The present observations can be considered as experimental evidence of the existence of the “island of stability” of superheavy elements