Most commonly, this refers to 511-keV photons produced by an electron interacting with a positron. These photons are frequently referred to as gamma rays, despite having their origin outside the nucleus, due to unclear distinctions between types of photon radiation.
Most commonly, these refer to 511-keV photons generated by an electron colliding with a positron. Such photons are often called gamma rays, despite their origin outside the nucleus, due to ambiguous distinctions between types of photon radiation.