  Measurements of high-energy photons from cosmic sources of nuclear radiation
through ESA's INTEGRAL mission have advanced our knowledge: New data with high
spectral resolution showed that characteristic gamma-ray lines from radioactive
decays occur throughout the Galaxy, in its interstellar medium and from
sources. Although the number of detected sources and often the significance of
the astrophysical results remain modest, conclusions derived from this unique
astronomical window of radiation originating from nuclear processes are
important, complementing the widely-employed atomic-line based spectroscopy. We
review the results and insights obtained in the past decade from gamma-ray line
measurements of cosmic sources, in the context of their astrophysical
questions.
