The 13C-Pocket Structure in AGB Models: Constraints from Zirconium   Isotope Abundances in Single Mainstream SiC Grains
  We present postprocess AGB nucleosynthesis models with different $^{13}$C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. (1997) and Barzyk et al. (2007). We show that higher-than-solar $^{92}$Zr/$^{94}$Zr ratios can be predicted by adopting a $^{13}$C-pocket with a flat $^{13}$C profile, instead of the previous decreasing-with-depth $^{13}$C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat $^{13}$C profile based on barium isotopes in mainstream SiC grains by Liu et al. (2014). 
Nan Liu, Roberto Gallino, Sara Bisterzo, Andrew M. Davis, Michael R.   Savina and Michael J. Pellin
astro-ph.SR