Reexamining the temperature and neutron density conditions for r-process nucleosynthesis with augmented nuclear mass models

TL;DR

This study investigates how different nuclear mass models influence the conditions needed for r-process nucleosynthesis, revealing insights into abundance peak formation and the impact of nuclear mass uncertainties on astrophysical models.

Contribution

It introduces an analysis of four augmented nuclear mass models to determine r-process conditions and highlights key nuclei for future precise mass measurements.

Findings

Different conditions are needed for producing abundance peaks at A ~ 80 and 195.

Conditions for A ~ 130 and 195 peaks can overlap, enabling coproduction.

Mass uncertainties affect r-process conditions and identify key nuclei for measurements.

Abstract

We explore the effects of nuclear masses on the temperature and neutron density conditions required for r-process nucleosynthesis using four nuclear mass models augmented by the latest atomic mass evaluation. For each model we derive the conditions for producing the observed abundance peaks at mass numbers A ~ 80, 130, and 195 under the waiting-point approximation and further determine the sets of conditions that can best reproduce the r-process abundance patterns (r-patterns) inferred for the solar system and observed in metal-poor stars of the Milky Way halo. In broad agreement with previous studies, we find that (1) the conditions for producing abundance peaks at A ~ 80 and 195 tend to be very different, which suggests that, at least for some nuclear mass models, these two peaks are not produced simultaneously; (2) the typical conditions required by the critical waiting-point (CWP) nuclei with the N = 126 closed neutron shell overlap significantly with those required by the N=82 CWP nuclei, which enables coproduction of abundance peaks at A ~ 130 and 195 in accordance with observations of many metal-poor stars; and (3) the typical conditions required by the N = 82 CWP nuclei can reproduce the r-pattern observed in the metal-poor star HD 122563, which differs greatly from the solar r-pattern. We also examine how nuclear mass uncertainties affect the conditions required for the r-process and identify some key nuclei including76Ni to 78Ni, 82Zn, 131Cd, and 132Cd for precise mass measurements at rare-isotope beam facilities.