Strong enhancement of dynamical emission of heavy fragments in the neutron-rich ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ reaction at $35A$ MeV

A quantitative comparison is made between the absolute cross sections associated with statistical and dynamical emission of heavy fragments in the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ collisions experimentally investigated at 35$A$ MeV beam energy using the multidetector CHIMERA. The result shows that the dynamical process is about twice as probable in the neutron-rich ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ system as in the ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ neutron-poor one. This unexpected and significant difference indicates that the reaction mechanism is strongly dependent on the entrance-channel isospin ($N/Z$) content.

Figure 1

Invariant $V_{\mathrm{per}}$ versus $V_{\mathrm{par}}$ cross-section plots for the light fragment of the PLF breakup in the ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ reaction. Different panels correspond to different values of mass asymmetry $A_H/A_L$ and the total kinetic energy $E_{2F}=E_H+E_L$. The distributions are shown in logarithmic scale. The red color corresponds to the largest cross sections and the arrows indicate the beam velocity.

Figure 2

“In-plane” angular distributions of the PLF breakup fragments for the ${}^{124}\mathrm{Sn}+{}^{64}\mathrm{Ni}$ (full circles) and ${}^{112}\mathrm{Sn}+{}^{58}\mathrm{Ni}$ (empty triangles) reactions at 35$A$ MeV for different bins of the total kinetic energy ($E_{2F}$) and fragment mass asymmetry ($A_H/A_L$). According to the adopted convention [11], for ${\Phi }_{\mathrm{plane}}=0^{°}$ the heavier of the two fragments is emitted forward, along the PLF flight direction.

Figure 3

Mean values of the relative velocity ($V_{\mathrm{rel}}$) of the PLF breakup fragments normalized to the value corresponding to the Viola systematics ($V_{\mathrm{Viola}}$), as a function of the in-plane angle for different bins of the total kinetic energy ($E_{2F}$) and fragment mass asymmetry ($A_H/A_L$), for neutron-rich (full circles) and neutron-poor (empty triangles) $\mathrm{Sn}+\mathrm{Ni}$ systems.