The role of near neutron drip-line nuclei in the $r$-process

The role of near neutron-drip-line nuclei in the rapid neutron-capture process ($r$-process) is studied with the classical $r$-process model. Simulations under different astrophysical conditions ($T$, $n_n$) show that $r$-process paths approach the neutron-drip line under low-temperature and high-neutron-density conditions. A sensitivity study reveals that variations in the nuclear masses of these exotic nuclei significantly impact the abundances of superheavy nuclei, and lead to obvious abundance variations in the $A=110-125$, $A=175-185$, and $A=200-205$ regions. By contrast, the $r$-process rare-earth peak and the $A=130,195$ peaks remain largely unaffected. The nuclei that obviously impact $r$-process abundances are mainly distributed in the region of $25\le Z\le 90$ and $50\le N\le 180$, with the nuclei around neutron magic numbers found to be particularly important for the $r$-process, even in the near-neutron-drip-line region.