  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.
