C.H. Dasso

Dynamics of the shell model

Abstract Many Fermi liquids are amenable to a shell-model description, where the particles move in an average potential. The coupling of the single-particle degrees of freedom to other modes of excitation strongly affects the properties of the shell-model potential. It is empirically found, however, that these couplings preserve the approximate validity of the shell model. Significant theoretical progress has recently been accomplished in the understanding of the resulting “dynamical shell model” in nuclear matter, normal liquid 3He, the electron gas and nuclei. The dominant modes which couple to the single-particle motion are particle-hole excitations in the case of nuclear matter, paramagnons in the case of 3He, phonons for electrons in metals and surface vibrations in the case of nuclei. For the latter, the dynamical shell model can be viewed as an extension of the optical model to encompass both positive and negative energies. It thus provides a unified description of scattering and of bound single-particle states. The associated potential is energy dependent. This feature is characterized by the nucleon effective mass. The theoretical and experimental evidence which testifies to the existence of a strong energy dependence of this effective mass around the Fermi energy and near the nuclear surface is the central subject of the present review.

Channel-coupling effects in heavy-ion fusion reactions

Abstract A coupled-channel framework for fusion reactions is considered where an ingoing-wave boundary condition allows the effect of strong coupling in the barrier region to be studied. It is shown analytically within the sudden limit and, more generally, with model calculations that the couplings to reaction channels act to enhance the transmission through the barrier at low energies. This appears to be a natural mechanism for explaining the relatively large sub-barrier heavy-ion fusion cross sections which have recently been observed.

A study of Q-value effects on barrier penetration

Abstract Coupled-channel equations for barrier penetration problems are solved analytically to show the effects which finite Q-values have on the total transmission function.

Role of breakup processes in fusion enhancement of drip-line nuclei at energies below the Coulomb barrier

We carry out realistic coupled-channels calculations for

The role of the giant resonances in deep inelastic collisions between heavy ions

^{11}

Estimate of enhancements in sub-barrier heavy-ion fusion cross sections due to coupling to inelastic and transfer reaction channels

Be +

Damping of single-particle states and giant resonances in208Pb

^{208}

Deep inelastic collisions between heavy ions

Pb reaction in order to discuss the effects of break-up of the projectile nucleus on sub-barrier fusion. We discretize in energy the particle continuum states, which are associated with the break-up process, and construct the coupling form factors to these states on a microscopic basis. The incoming boundary condition is employed in solving coupled-channels equations, which enables us to define the flux for complete fusion inside the Coulomb barrier. It is shown that complete fusion cross sections are significantly enhanced due to the couplings to the continuum states compared with the no coupling case at energies below the Coulomb barrier, while they are hindered at above barrier energies.

Macroscopic formfactors for pair transfer in heavy ion reactions

Abstract A unified description of heavy ion reactions which includes all the most important nuclear degrees of freedom in an average way is attempted, in terms of the semiclassical coupled equations.

Formfactors for inelastic scattering between heavy ions

Abstract Sub-barrier fusion cross sections for 40 Ar + 122 Sn , 58 Ni + 58 Ni and 58 Ni + 64 Ni are estimated using a simplified model to account for couplings to inelastic excitation and transfer reaction channels. Couplings to inelastic modes generally account for the bulk of the sub-barrier cross sections. In the case of 58 Ni + 64 Ni , positive Q -value transfer reaction channels are required to explain the trend of the low-energy fusion data.