Source of the Rare-Earth Element Peak inr-Process Nucleosynthesis

Abstract

We use network calculations of $r$-process nucleosynthesis to pin down the origin of the peak in the solar $r$-process abundance distribution near nuclear mass number $A\approx 160$. The peak is due to a subtle interplay of nuclear deformation and $\beta$ decay, and forms not in the steady phase of the $r$ process, but only just prior to freeze-out, as the free neutrons rapidly disappear. Its existence should therefore help constrain the conditions under which the $r$ process freezes out.