Evidence for Widespread 26Al in the Solar Nebula and Constraints for Nebula Time Scales

摘要: A search was made for ^(26)Mg (^(26)Mg^*) from the decay of ^(26)Al (half-life = 0.73 million years) in Al-rich objects unequilibrated ordinary chondrites. Two Ca-Al-rich inclusions (CAIs) and two chondrules (not CAIs) were found that contained when they formed. Internal isochrons CAIs yielded an initial ^(26)Al/^(27)Al ratio [(^(26)Al/^(27)Al)_0] 5 x 10^(-5), indistinguishable most carbonaceous This result shows with this level are present throughout classes chondrites strengthens notion widespread early solar system. The have lower ^(26)Mg^*, corresponding to a (^(26)Al/^(27)Al)_0 approximately 9 10^(-6). Five other contain no resolvable ^(26)Mg^*. If formed isotopically homogeneous reservoir, then must or been last altered ~2 years after formed; ^(26)Mg^*-free >1 3 later still. Because ^(26)Mg^*-containing both Chainpur, which not heated more than ~400oC, it follows parent body metamorphism cannot explain absence ^(26)Mg^* some these chondrules. Rather, its indicates lifetime nebula over extended ~5 years.