  The mixing of ejecta from young stars into the interstellar medium is an
important process in the interplay between star formation and galaxy evolution.
A unique window into these processes is provided by the radioactive isotopes
$^{26}$Al, traced by its $\gamma$-ray decay lines at 1.8 MeV. With a mean
lifetime of $\sim$1 Myr it is a long-term tracer of nucleosynthesis for massive
stars. Our population synthesis code models the ejection of $^{26}$Al, together
with the $^{60}$Fe, the kinetic energy and UV radiation for a population of
massive stars. We have applied the code to study the nearby Orion region and
the more massive Carina region and found good agreement with observational
constraints.
