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The nucleosynthesis and ejection of radioactive $^{26}$Al (t$_{1/2} \sim$0.72\,Myr) and $^{60}$Fe, (t$_{1/2} \sim$ 2.5\,Myr) into the interstellarmedium is dominated by the stellar winds of massive stars and supernova type IIexplosions. Studies of meteorites and their components indicate that theinitial abundances of these short-lived radionuclides in the solarprotoplanetary disk were higher than the background levels of the galaxyinferred from $\gamma$--ray astronomy and models of the galactic chemicalevolution. This observation has been used to argue for a late-stage addition ofstellar debris to the Solar System's parental molecular cloud or,alternatively, the solar protoplanetary disk, thereby requiring a specialscenario for the formation of our Solar System. Here, we use supercomputers tomodel---from first principles---the production, transport and admixing offreshly synthesized $^{26}$Al and $^{60}$Fe in star-forming regions withingiant molecular clouds. Under typical star-formation conditions, the levels of$^{26}$Al in most star-forming regions are comparable to that deduced frommeteorites, suggesting that the presence of short-lived radionuclides in theearly Solar System is a generic feature of the chemical evolution of giantmolecular clouds. The $^{60}$Fe/$^{26}$Al yield ratio of $\approx 0.2$calculated from our simulations is consistent with the galactic value of 0.15$\pm$ 0.06 inferred from $\gamma$--ray astronomy but is significantly higherthan most current Solar System measurements indicate. We suggest that estimatesbased on differentiated meteorites and some chondritic components may not berepresentative of the initial $^{60}$Fe abundance of the bulk Solar System.

Abundance of 26Al and 60Fe in evolving Giant Molecular Clouds