Abstract
The existence of the dynamical dipole mode in the 192 Pb composite system was investigated through the study of its prompt γ decay employing the 40 Ca + 152 Sm and 48 Ca + 144 Sm reactions at E lab =11 and 10.1 MeV/u, respectively. The γ -rays and light charged particles were detected in coincidence with evaporation residues and fission fragments. First results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole γ radiation could be of interest for the synthesis of super-heavy elements through ”hot” fusion reactions. Furthermore, by using radioactive beams and the prompt γ radiation as a probe we could get information on the symmetry energy at sub-saturation densities.
Highlights
The dynamical dipole mode is a large amplitude collective oscillation of protons against neutrons that develops along the symmetry axis of the dinuclear system formed in charge asymmetric heavy-ion collisions [1]
It decays emitting prompt γ radiation with the following characteristics: (i) it appears as an extra yield in the γ-ray energy spectra at a centroid energy lower than that of the Giant Dipole Resonance (GDR) thermally excited in the compound nucleus (CN) because it originates from a highly deformed dinuclear system; (ii) an anisotropic angular distribution due to the fact that the oscillation is confined in the reaction plane; (iii) an intensity depending on the reaction dynamics and on the incident energy [2]
In order to verify experimentally if this preequilibrium effect survives in heavier systems than those studied up to now, we extended our investigation of the dynamical dipole mode in the mass region of the 192Pb CN employing the 40Ca+152Sm and 48Ca+144Sm reactions at Elab=440 MeV and 485 MeV, respectively
Summary
The dynamical dipole mode is a large amplitude collective oscillation of protons against neutrons that develops along the symmetry axis of the dinuclear system formed in charge asymmetric heavy-ion collisions [1]. From an experimental point of view, the dynamical dipole mode has been observed in charge asymmetric heavy-ion deep inelastic [6,7,8] and fusion reactions [7, 9, 10] while the first systematic study of its features (centroid energy, width, intensity) as a function of the incident energy was performed in our previous campaign of experiments [11,12,13,14] where compound nuclei in the 132Ce mass region were created In those measurements, the 132Ce CN was formed through different charge asymmetry entrance channels at identical excitation energy and with identical spin distribution by using two reaction pairs: 32,36S+100,96Mo at Elab= 6 and 9 MeV/u and 36,40Ar+96,92Zr at Elab= 16 MeV/u. The experimental findings will be compared with theoretical predictions performed within a BNV transport model, based on a collective bremsstrahlung analysis of the entrance channel reaction dynamics [2]
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