Search for: All records

Abstract We develop recursive relations among abundances in anr-process network evolving neutron captures, photodisintegrations and beta decays through the use of the matrix-tree and matrix-forest theorems. Since these theorems are based on results from graph theory, we term the relations the GrRproc (GraphicalR-process) relations. We validate the relations by using them to computer-process abundances in network calculations in different astrophysical environments. We also illustrate how they can be used to follow complex reaction flows quantitatively in an evolvingr-process network through the concept of contribution paths. Such contribution paths show how particular reactions govern the evolution of abundance features during the nucleosynthesis and, consequently, can clarify the role of key nuclear data and astrophysical environments in that evolution. The Python open-source package that implements the tool is freely available. 

Abstract Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth^1,2. Among such nuclei whose decay signatures are found in the oldest meteorites,²⁰⁵Pb is a powerful example, as it is produced exclusively by slow neutron captures (thesprocess), with most being synthesized in asymptotic giant branch (AGB) stars^3–5. However, making accurate abundance predictions for²⁰⁵Pb has so far been impossible because the weak decay rates of²⁰⁵Pb and²⁰⁵Tl are very uncertain at stellar temperatures^6,7. To constrain these decay rates, we measured for the first time the bound-state β⁻decay of fully ionized²⁰⁵Tl⁸¹⁺, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate⁸and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate²⁰⁵Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the²⁰⁵Pb/²⁰⁴Pb ratio from meteorites^9–11, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the others-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun’s birth as a long-lived, giant molecular cloud and support the use of the²⁰⁵Pb–²⁰⁵Tl decay system as a chronometer in the early Solar System.