Document Type


Publication Date

Fall 9-20-1993

Publication Title

The Astrophysical Journal


The American Astronomical Society


Several authors have shown that massive stars exploding at a rate of about three per century can account for a large portion, if not all, of the observed interstellar 26Al. In a separate argument using models of Galatic chemical evolution, Clayton (1984) showed that the 26Al/27Al production ratio was not large enough to maintain enought 26Al in the Galactic disk gas of ~ 10^10 M⊙ having solar composition. We present a resolution of those conflicting arguments. A past history of Galactic infall growing the Galatic disk so dilutes the stable 27Al concentration that the two approaches can be brought into near agreement. If massive stars dominate the production of 26Al, we suggest that the apparent shortfall of their 26Al/27Al yield ratio is to be interpreted as evidence for signigicant growth of the Galactic disk. We also discuss the implications of these arguments for other extinct radioactivites in meteories, using 129I and 146Sm as examples.