Description:Exotic excitation modes in atomic nuclei far from stability
Abstract:Collective degrees of freedom characterize many aspects of nuclear structure. Furthermore, the multipole response of nuclei far from the stability line and the possible occurrence of exotic modes of excitation presents a rapidly growing field of research. This work is directed to the study of the existence and of properties of the pygmy dipole resonance (PDR), i.e., the resonant oscillation of the weakly-bound neutron skin against the isospin saturated proton-neutron core, in medium-mass and heavy nuclei. In fact, since the interpretation of the dynamics of the observed low-energy dipole strength in nuclei with a pronounced neutron excess is currently under discussion, a theoretical analysis of its properties can be very useful.
The main steps of our analysis are the following. First of all, we solve the Harte-Fock equations, in order to fix the single particle basis, and we determine the collective excitations of the system by using the Random Phase Approximation. By means of a mapping procedure, we construct the boson images (phonons) of the RPA modes and we diagonalize the Hamiltonian in the space containing up to three phonons. In such a way, we can improve the standard harmonic RPA description by taking into account anharmonic effects. From a numerical point of view, the mapping procedure is highly time consuming. For example, in the case of 140Sn, one has to calculate approximately 500 matrix elements in order to construct the boson image of the Hamiltonian and the calculation of each matrix element requires about 1 hour. So, by using only one CPU, it would take a very large time (\~20 days), while, by using PI2S2 grid infrastructure, we can obtain our results within 1-2 hours (with 200-250 CPUs). So, the use of the PI2S2 resource has made possible to carry out a systematic analysis of several Sn isotopes (from 100Sn to 140Sn) by using several interactions (SGII, SLY4,\.\.\.). Preliminary results are interesting and very promising.
<BR><BR><B>Software requirements</B>: Compilatore F77 e F90,slatex^