SOURCE OF THE RARE-EARTH ELEMENT PEAK IN R-PROCESS NUCLEOSYNTHESIS

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