Distributed radioactivities

Abstract

Radioactive isotopes are ejected into the surroundings of their sources, and become observable through their gamma-ray line emission once having left dense production sites from where not even gamma-rays may escape. Nuclear gamma-rays can penetrate material layers of integrated thickness of a few grams/cm2. A typical interstellar cloud would have ∼0.1 g/cm 2, SNIa envelopes are transparent to gamma-rays after 30-100 days, depending on explosion dynamics. In this chapter, we discuss such radioactivities in interstellar space. Depending on radioactive lifetime, we thus address isotopes which originate from single sources (the short-lived isotopes) or up to thousands of sources as accumulated in interstellar space over the radioactive lifetime of long-lived isotopes (see Table 7.1).