  Measurement and astrophysical interpretation of characteristic gamma-ray
lines from nucleosynthesis was one of the prominent science goals of the
INTEGRAL mission and in particular its spectrometer SPI. Emission from 26Al and
from 60Fe decay lines originates from accumulated ejecta of nucleosynthesis
sources, and appears diffuse in nature. 26Al and 60Fe are believed to originate
mostly from massive star clusters. Gamma-ray observations open an interesting
window to trace the fate and flow of nucleosynthesis ejecta, after they have
left the immediate sources and their birth sites, and on their path to mix with
ambient interstellar gas. The INTEGRAL 26Al emission image confirms earlier
findings of clumpiness and an extent along the entire plane of the Galaxy,
supporting its origin from massive-star groups. INTEGRAL spectroscopy resolved
the line and found Doppler broadenings and systematic shifts from large-scale
galactic rotation. But an excess velocity of ~200 km/s suggests that 26Al
decays preferentially within large superbubbles that extend in forward
directions between spiral arms. The detection of 26Al line emission from nearby
Orion and the Eridanus superbubble supports this interpretation. Positrons from
beta+ decays of 26Al and other nucleosynthesis ejecta have been found to not
explain the morphology of positron annihilation gamma-rays at 511 keV that have
been measured by INTEGRAL. The 60Fe signal measured by INTEGRAL is diffuse but
too weak for an imaging interpretation, an origin from point-like/concentrated
sources is excluded. The 60Fe/26Al ratio is constrained to a range 0.2-0.4.
Beyond improving precision of these results, diffuse nucleosynthesis
contributions from novae (through 22Na radioactivity) and from past neutron
star mergers in our Galaxy (from r-process radioactivity) are exciting new
prospects for the remaining mission extensions.
