Isospin effects on the energy of peak mass production

Abstract

Using the isospin-dependent quantum molecular dynamics model, we study the isospin effects on the peak center-of-mass energy (${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$) and peak multiplicity of intermediate mass fragments (${\ensuremath{\langle}{N}_{\text{IMF}}\ensuremath{\rangle}}^{\mathrm{max}}$). We compare our theoretical calculations (for stable systems) with experimental data and find a good agreement. We further extend this study to neutron-rich colliding pairs. We find that ${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$ is insensitive to neutron content for the isotopic colliding pairs due to the intermixing of mass and isospin effects, while for the isobaric pairs, ${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$ decreases with increase in the $N/Z$ ratio of the system. We also demonstrate clearly the dominance of symmetry energy over Coulomb repulsion. We also find that ${\ensuremath{\langle}{N}_{\text{IMF}}\ensuremath{\rangle}}^{\mathrm{max}}$ increases with the system mass but is insensitive to the isospin degree of freedom.