Evidence of dynamical dipole excitation in the fusion-evaporation of theCa40+Sm152heavy system

Abstract

The excitation of the dynamical dipole mode along the fusion path was investigated for the first time in the formation of a heavy compound nucleus in the A ∼ 190 mass region. The compound nucleus was formed at identical conditions of excitation energy and spin from two entrance channels: the charge-asymmetric 40 Ca + 152 Sm and the nearly charge-symmetric 48 Ca + 144 Sm at E lab = 11 and 10.1 MeV/nucleon, respectively. High-energy γ rays and light charged particles were measured in coincidence with evaporation residues by means of the MEDEA multidetector array (Laboratori Nazionali del Sud, Italy) coupled to four parallel plate avalanche counters. The charged particle multiplicity spectra and angular distributions were used to pin down the average excitation energy, the average mass, and the average charge of the compound nucleus. The γ -ray multiplicity spectrum and angular distribution related to the nearly charge-symmetric channel were employed to obtain new data on the giant dipole resonance in the compound nucleus. The dynamical dipole mode excitation in the charge-asymmetric channel was evidenced, in a model-independent way, by comparing the γ -ray multiplicity spectra and angular distributions of the two entrance channels with each other. Calculations of the dynamical dipole mode in the 40 Ca + 152 Sm channel, based on a collective bremsstrahlung analysis of the reaction dynamics, are presented. Possible interesting implications in the superheavy-element quest are discussed.

The Symmetry Energy of the Nuclear EoS: A Study of Collective Motion and Low-Energy Reaction Dynamics in Semiclassical Approaches

“…We first discuss dipole oscillations, following a collective bremsstrahlung analysis [27,36,38]. Similarly to Eq.…”

“…Since the transient composite system might experience large prolate deformation with respect to the equilibium configuration of the final compound nucleus, the corresponding pre-equilibrium radiation carries out fundamental information about the density distribution and the shape of the di-nuclear complex. It is worth noting that this mechanism may also provide a cooling effect, which could favour superheavy element formation [35,36].…”

Pre-equilibrium effects in charge-asymmetric low-energy reactions

“…In (incomplete) fusion reactions, the shape of the pre-equilibrium dinuclear complex exhibits a very large prolate deformation as compared to the shape finally reached by the equilibrated compound nucleus. Consequently, the preequilibrium radiation carries out relevant information about the shape of the system, as well as insight into the charge equilibration, and provides a cooling effect along the fusion path, possibly favoring the formation of superheavy elements [11,12]. Thus one expects the DD to be influenced by different parameters, like charge and mass asymmetry, collision centrality and energy [3,9,13].…”