  The Cygnus region harbours a huge complex of massive stars at a distance of
1.0-2.0kpc from us. About 170 O stars are distributed over several OB
associations, among which the Cyg OB2 cluster is by far the most important with
about 100-120 O stars. These massive stars inject large quantities of
radioactive nuclei into the interstellar medium, such as 26Al and 60Fe, and
their gamma-ray line decay signals can provide insight into the physics of
massive stars and core-collapse supernovae. Past studies of the nucleosynthesis
activity of Cygnus have concluded that the level of 26Al decay emission as
deduced from CGRO/COMPTEL observations was a factor 2-3 above the predictions
based on the theoretical yields available at that time and on the observed
stellar content of the Cygnus region. We reevaluate the situation from new
measurements of the gamma-ray decay fluxes with INTEGRAL/SPI and new
predictions based on recently improved stellar models including some of the
effects of stellar rotation for the higher mass stars and a coherent estimate
of the contribution from SNIb/c. We developed a population synthesis code to
predict the nucleosynthesis activity and corresponding decay fluxes of a given
stellar population of massive stars. The observed decay fluxes from the Cygnus
complex are found to be consistent with the values predicted by population
synthesis at solar metallicity. The observed extent of the 1809keV emission
from Cygnus is found to be consistent with the result of a numerical simulation
of the diffusion of 26Al inside the superbubble blown by Cyg OB2. Our work
indicates that the past dilemma regarding the gamma-ray line emission from
Cygnus resulted from an overestimate of the 1809keV flux of the Cygnus complex,
combined with an underestimate of the nucleosynthesis yields.
