Reverse engineering nuclear properties from rare earth abundances in the $r$ process

TL;DR

This paper uses inverse modeling and Monte Carlo simulations to deduce nuclear properties from rare earth element abundances, aiming to better understand the astrophysical conditions of the r process.

Contribution

It introduces a reverse engineering approach combining nuclear physics and astrophysical modeling to infer unknown nuclear properties from observed abundance patterns.

Findings

Different astrophysical conditions lead to distinct nuclear property predictions.

Targeted experiments can constrain the astrophysical site of the r process.

The method provides insights into nuclear properties far from stability.

Abstract

The bulk of the rare earth elements are believed to be synthesized in the rapid neutron capture process or $r$ process of nucleosynthesis. The solar $r$-process residuals show a small peak in the rare earths around $A\sim 160$, which is proposed to be formed dynamically during the end phase of the $r$ process by a pileup of material. This abundance feature is of particular importance as it is sensitive to both the nuclear physics inputs and the astrophysical conditions of the main $r$ process. We explore the formation of the rare earth peak from the perspective of an inverse problem, using Monte Carlo studies of nuclear masses to investigate the unknown nuclear properties required to best match rare earth abundance sector of the solar isotopic residuals. When nuclear masses are changed, we recalculate the relevant $\beta$-decay properties and neutron capture rates in the rare earth region. The feedback provided by this observational constraint allows for the reverse engineering of nuclear properties far from stability where no experimental information exists. We investigate a range of astrophysical conditions with this method and show how these lead to different predictions in the nuclear properties influential to the formation of the rare earth peak. We conclude that targeted experimental campaigns in this region will help to resolve the type of conditions responsible for the production of the rare earth nuclei, and will provide new insights into the longstanding problem of the astrophysical site(s) of the $r$ process.