Dipolar degrees of freedom and isospin equilibration processes in heavy ion collisions

Abstract

Background: In heavy ion collision at the Fermi energies Isospin equilibration processes occurring when nuclei with different charge/mass asymmetries interacts have been investigated to get information on the nucleon-nucleon Iso-vectorial effective interaction.Purpose: In this paper, for the system 48 Ca + 27 Al at 40 MeV/nucleon, we investigate on this process by means of an observable tightly linked to isospin equilibration processes and sensitive in exclusive way to the dynamical stage of the collision. From the comparison with dynamical model calculations we want also to obtain information on the Iso-vectorial effective microscopic interaction. Method:The average time derivative of the total dipole associated to the relative motion of all emitted charged particles and fragments has been determined from the measured charges and velocities by using the 4π multi-detector CHIMERA. The average has been determined for semiperipheral collisions and for different charges Z b of the biggest produced fragment. Experimental evidences collected for the systems 27 Al+ 48 Ca and 27 Al+ 40 Ca at 40 MeV/nucleon used to support this novel method of investigation are also discussed.Results: The data analysis shows a clear signature of a trend to the global Isospin equilibration of the system for increasing differences of the Z b values with respect to the projectile charge. Conclusions:The comparison with CoMD-II calculations gives the best agreement with data using a stiffness γ value for the Iso-vectorial interaction in the range γ ≃ 1−1.2. Moreover, the same comparison allows to estimate the non-negligible contribution to the global isospin equilibration process given by the un-detected emitted neutrons.

Nuclear Equation of State and many-body phase-space correlations in the Constrained Molecular Dynamics

“…To test the different effective interactions, these approaches are used as a bridge to connect the information collected from heavy-ion collisions to the NM equation of state (EoS)(see as some examples Refs. [23,24,25].…”

“…Other conditions have been chosen corresponding to the vanishing of the total energy at zero density and no back-bending in the density range 2÷3ρ 0 . Finally, different values of the slope parameter associated to the symmetry energy L = 3ρ 0 ( dEsym dρ ) ρ 0 have been considered changing in the range 55 ÷ 105 MeV as suggested from different investigations [17,26,23,25,27].…”

Transport Model Comparison Studies of Intermediate-Energy Heavy-Ion Collisions

“…CoMD calculations have been performed to describe the dynamics of the isospin equilibration phenomenon and the connection to the density dependence of the symmetry energy [365][366][367][368].…”