Positioning the neutron drip line and the r-process paths in the nuclear landscape

Abstract

Exploring nucleon drip lines and astrophysical rapid neutron capture process (r-process) paths in the nuclear landscape is extremely challenging in nuclear physics and astrophysics. While various models predict similar proton drip line, their predictions for neutron drip line and the r-process paths involving heavy neutron-rich nuclei exhibit a significant variation which hampers our accurate understanding of the r-process nucleosynthesis mechanism. Using microscopic density functional theory with a representative set of non-relativistic and relativistic interactions, we demonstrate for the first time that this variation is mainly due to the uncertainty of nuclear matter symmetry energy $E_{\rm{sym}}(\rho_{\rm{sc}})$ at the subsaturation cross density $\rho_{\rm{sc}}=0.11/0.16\times\rho_0$ ($\rho_0$ is saturation density), which reflects the symmetry energy of heavy nuclei. Using the recent accurate constraint on $E_{\rm{sym}}(\rho_{\rm{sc}})$ from the binding energy difference of heavy isotope pairs, we obtain quite precise predictions for the location of the neutron drip line, the r-process paths and the number of bound nuclei in the nuclear landscape. Our results have important implications on extrapolating the properties of unknown neutron-rich rare isotopes from the data on known nuclei.