EVIDENCE FOR WIDESPREAD AL-26 IN THE SOLAR NEBULA AND CONSTRAINTS FORNEBULA TIME SCALES

qA search was made for Mg-26 (Mg-26) from the decay of Al-26 (half-li fe = 0.73 million years) in Al-rich objects from unequilibrated ordina ry chondrites. Two Ca-Al-rich inclusions (CAls) and two Al-rich chondr ules (not CAls) were found that contained Al-26 when they formed. Inte rnal isochrons for the CAls yielded an initial Al-26/Al-27 ratio [(Al- 26/Al-27)(0)] of 5 x 10(-5), indistinguishable from most CAls in carbo naceous chondrites. This result shows that CAls with this level of Al- 26 are present throughout the classes of chondrites and strengthens th e notion that Al-26 was widespread in the early solar system. The two Al-rich chondrules have lower Mg-26, corresponding to a (Al-26/Al-27) (0) ratio of similar to 9 x 10(-6). Five other Al-rich chondrules cont ain no resolvable Mg-26. If chondrules and CAls formed from an isotop ically homogeneous reservoir, then the chondrules with Al-26 must have formed or been last altered similar to 2 million years after CAls for med; the Mg-26-free chondrules formed > 1 to 3 million years later st ill, Because Mg-26-containing and Mg-26*-free chondrules are both fou nd in Chainpur, which was not heated to more than similar to 400 degre es C, it follows that parent body metamorphism cannot explain the abse nce of Mg-26 in some of these chondrules. Rather, its absence indicat es that the lifetime of the solar nebula over which CAls and chondrule s formed extended over similar to 5 million years.