We discuss the synthesis of some short-lived isotopes and of ^ { 23 } Na in thermally pulsing AGB stars with initial mass of 2 M _ { \odot } and two different metallicities ( Z =1.5 \times 10 ^ { -2 } , corresponding to the metal amount in the present Sun , and Z =10 ^ { -4 } ) , representative of disk and halo stars , respectively . The different nucleosynthesis channels are illustrated in some details .
As previously found , the ^ { 13 } C formed after each third dredge up episode is usually completely consumed by \alpha captures before the onset of the subsequent thermal pulse , releasing neutrons .
This is the most efficient neutron source in low mass AGB stars , and the resulting s-process nucleosynthesis is at the origin of the solar main component .
However , in the solar metallicity model , we find that the temperature of the first formed ^ { 13 } C pocket remains too low during the interpulse and the ^ { 13 } C is not completely burnt , being partially engulfed in the convective zone generated by the following thermal pulse .
Due to the rapid convective mixing in this zone , the ^ { 13 } C is exposed to a larger temperature and a nucleosynthesis characterized by a relatively high neutron density develops .
The main effect is the strong enhancement of isotopes located beyond some critical branching in the neutron-capture path , like ^ { 60 } Fe , otherwise only marginally produced during a standard s-process nucleosynthesis .

– short-lived isotopes