Radioactive Decay

TL;DR

Radioactive decay in astrophysics involves gamma-ray emissions from unstable nuclei, providing insights into stellar processes, nucleosynthesis, and cosmic-ray interactions, crucial for understanding cosmic phenomena.

Contribution

This paper reviews how gamma-ray lines from radioactive isotopes reveal details about stellar interiors, explosions, and interstellar medium processes in an astrophysical context.

Findings

Gamma-ray lines from isotopes like $^{56}$Ni and $^{44}$Ti trace nucleosynthesis.

Radioactive decay observations complement supernova optical measurements.

Positron annihilation gamma-rays connect to radioactive isotopes.

Abstract

Radioactive decay of unstable atomic nuclei leads to liberation of nuclear binding energy in the forms of gamma-ray photons and secondary particles (electrons, positrons); their energy then energises surrounding matter. Unstable nuclei are formed in nuclear reactions, which can occur either in hot and dense extremes of stellar interiors or explosions, or from cosmic-ray collisions. In high-energy astronomy, direct observations of characteristic gamma-ray lines from the decay of radioactive isotopes are important tools to study the process of cosmic nucleosynthesis and its sources, as well as tracing the flows of ejecta from such sources of nucleosynthesis. These observations provide a valuable complement to indirect observations of radioactive energy deposits, such as the measurement of supernova light in the optical. Here we present basics of radioactive decay in astrophysical context, and how gamma-ray lines reveal details about stellar interiors, about explosions on stellar surfaces or of entire stars, and about the interstellar-medium processes that direct the flow and cooling of nucleosynthesis ashes once having left their sources. We address radioisotopes such as $^{56}$Ni, $^{44}$Ti, $^{26}$Al, $^{60}$Fe, $^{22}$Na, $^{7}$Be, and also how characteristic gamma-ray emission from the annihilation of positrons is connected to these.