Introduction to Astronomy with Radioactivity

In the late nineteenth century, Antoine Henri Becquerel discovered radioactivity and thus the physics of weak interactions, well before atomic and quantum physics was known. The different types of radioactive decay, alpha, beta, and gamma decay, all are different types of interactions causing the same, spontaneous, and time-independent decay of an unstable nucleus into another and more stable nucleus. Nuclear reactions in cosmic sites re-arrange the basic constituents of atomic nuclei (neutrons and protons) among the different configurations which are allowed by Nature, thus producing radioactive isotopes as a by-product. Throughout cosmic history, such reactions occur in different sites, and lead to rearrangements of the relative abundances of cosmic nuclei, a process called cosmic chemical evolution, which can be studied through the observations of radioactivity. The special role of radioactivity in such studies is contributed by the intrinsic decay of such material after it has been produced in cosmic sites. This brings in a new aspect, the clock of the radioactive decay. Observational studies of cosmic radioactivities intrinsically obtain isotopic information which are at the heart of cosmic nucleosynthesis. They are best performed by precision mass spectroscopy in terrestrial laboratories, which has been combined with sophisticated radiochemistry to extract meteoritic components originating from outside the solar system, and by spectroscopy of characteristic gamma-ray lines emitted upon radioactive decay in cosmic environments and measured with space-based telescopes. This book describes where and how specific astronomical messages from cosmic radioactivity help to complement the studies of cosmic nucleosynthesis sites anad of cosmic chemical evolution.