Exotic Cluster Structures in the Mean-Field Theory

Abstract

Abstract. Investigations of exotic cluster-like phenomena in the framework of the SkyrmeHartree-Fock approach are reported. The occurrence of highly excited isomeric states is discussed in connection with the question of their stability in static and time-dependent Hartree Fock (TDHF) calculations. We find rotational stabilization of a 4α chain structure in 16 O occurring for a limited range of angular momenta. A toroidal configuration of 40 Ca was also stabilized by rotation and provides a very interesting example of rotation about a symmetry axis with a strictly quantized total angular momentum. Finally we look at the formation of nuclear pasta phases in a time-dependent approach and their classification. Complex isomeric states in Hartree-Fock calculationsIn an early paper on cluster structure of light nuclei [1] it was already found that in Hartree-Fock calculations exotic configurations can appear that appear to be as stable as the ground state but upon closer examination are found to in reality be unstable against some type of collective deformation. Fig. 1 illustrates how this works in practice: a chain configuration of three α-particles remains stable for several thousand static iterations in a Hartree-Fock code but then suddenly switches over to the ground state of 12 C via a bending deformation described by the Q 31 multipole accompanied by a drastic change in quadrupole deformation β. It is especially interesting in this context that the typical convergence criteria like the relative change in energy per iteration ΔE and uncertainty in the singleparticle energies Δh are at the same level for the chain state as for the ground state.