Mechanisms of rare-earth r-process peak formation

Determine the physical mechanisms responsible for the formation of the rare-earth r-process abundance peak around mass number A≈165 by ascertaining whether the dominant cause is (i) a nearby subshell closure or strong nuclear deformation in the N≈104 region, (ii) a double asymmetric fission fragment distribution arising from fission recycling of heavier nuclei, or (iii) a combination of these effects.

Background

The paper investigates neutron-rich rare-earth isotopes near the N=104 midshell using high-precision mass spectrometry and examines their impact on astrophysical rapid neutron-capture (r-process) nucleosynthesis. The rare-earth abundance peak around A≈165 is sensitive to nuclear masses in this region, and improved mass measurements help constrain neutron-capture rates and r-process abundance predictions.

Despite extensive theoretical and experimental work, the physical origin of the rare-earth abundance peak remains unresolved. Candidate explanations include structural effects such as subshell closures or strong deformation in the N≈104 region, as well as influences from fission recycling that produce characteristic fragment distributions. The study’s new mass data provide inputs to test these scenarios but do not themselves settle the underlying mechanism.