Impact of Decay-Chain Feeding by Long-Lived Heavy Nuclei on Nuclear Cosmochronology

Abstract Nuclear cosmochronology provides an independent method for determining the ages of astrophysical objects without relying on Galactic chemical evolution models. Long-lived radioactive actinides synthesized via the rapid neutron-capture process (r-process) particularly thorium and uranium serve as ideal chronometric nuclei. However, predicting the initial abundances of these nuclei and their subsequent long-term evolution remains a major source of uncertainty in nuclear cosmochronology. In this work, we investigate the impact of decay-chain feeding from long-lived progenitor nuclei on nuclear cosmochronology and estimate the corresponding age corrections. We develop a self-consistent radioactive decay network that includes all relevant decay pathways and couple it to r-process nucleosynthesis calculations. By tracking the long-term evolution of r-process nucleosynthesis based on neutron star merger trajectories, the dominant long-lived nuclei shaping the evolution of the chronometric elements Th and U are identified as 232Th, 235U, 236U, 238U, and 244Pu. It is found that delayed feeding substantially modifies the long-term evolution of actinides particularly for 232Th, which receives significant late-time contributions from heavier progenitor nuclei such as 244Pu and 236U. As a consequence, the U/Th and Th/X chronometers exhibit significant sensitivity to delayed feeding from the progenitor nuclei 244Pu and 236U, with age corrections reaching ∼5 Gyr. These results suggest that decay-chain feeding from long-lived progenitor nuclei plays a crucial role in nuclear cosmochronology and should be properly accounted for in age determinations based on actinide chronometers.