On the production of Al-26 in the early solar system by low-energy oxygen cosmic rays

Clayton & Jin have proposed that the high abundance of Al-26 found in meteorites was produced by cosmic rays in the early solar system through the C-12(O-16,x)Al-26(gs) reaction. We have measured the yield of Al-26 in the ground state (i.e., Al-26(gs)) from this reaction and find that, if this mechanism produced the meteoritic Al-26, a substantial fraction of the solar system oxygen must have entered the solar system as low-energy cosmic rays. This does not seem plausible. If the proto-Sun itself was the source of the oxygen cosmic rays, they must have carried off some 5% of the power of the protosolar wind for 1 Myr. This too seems unlikely. Although we do not address the role of other cosmic-ray species in the production of Al-26, it appears that Al-26 was produced in a stellar environment, and not by cosmic rays.