Stellar origin of the 182Hf cosmochronometer and the presolar history of solar system matter

TL;DR

This paper reveals that the isotope 182Hf in the early solar system was produced by the slow neutron-capture process in asymptotic giant branch stars, refining the timeline of stellar events influencing solar system formation.

Contribution

It challenges previous assumptions by identifying the slow neutron-capture process as the source of 182Hf, providing new insights into the presolar history of solar system matter.

Findings

182Hf produced by slow neutron-capture in AGB stars

Last r-process event occurred ~100 million years before Sun formation

Last s-process event occurred ~30 million years before Sun formation

Abstract

Among the short-lived radioactive nuclei inferred to be present in the early solar system via meteoritic analyses, there are several heavier than iron whose stellar origin has been poorly understood. In particular, the abundances inferred for 182Hf (half-life = 8.9 million years) and 129I (half-life = 15.7 million years) are in disagreement with each other if both nuclei are produced by the rapid neutron-capture process. Here, we demonstrate that contrary to previous assumption, the slow neutron-capture process in asymptotic giant branch stars produces 182Hf. This has allowed us to date the last rapid and slow neutron-capture events that contaminated the solar system material at roughly 100 million years and 30 million years, respectively, before the formation of the Sun.