Low-lying dipole response within the second RPA in $^{40,48}$Ca nuclei
1 : Grand Accélérateur National d'Ions Lourds
(GANIL)
CEA/DSM-CNRS/IN2P3
The low-lying dipole strength distributions of $^{40}$Ca and $^{48}$Ca, in the energy region of the excitation spectrum between 5 and 10 MeV is studied within the second RPA with Skyrme interaction. Experimentally a significant amount of strength is found for $^{48}$Ca while RPA models do not usually predict any presence of strength in this energy region. On the contrary Second RPA calculations provide several low-lying states and many of them, despite being essentially 2 particle - 2 hole states, show quite large B(E1) values. These results are in reasonable agreement with other beyond mean-field predictions and with the corresponding experimental measurements. A detailed analysis of the properties of some of these states is done in terms of their 1 particle -1 hole nature, their transition densities and their collectivity. In particular, the coherence of the 1 particle-1 hole configurations in building the total transition probability is analyzed. The issue whether or not these states exhibit some features generally associated with the so-called pygmy dipole resonance is also addressed and discussed.
| Type : | : | Résumé |
| Thématiques | : | Physique nucléaire |
| PDF version | : |  PDF version |
