the Helium shell and, to a lesser extent, in the middle of the O shell.in the middle of the pre-SN convective C shell, by explosive O-burning and C-burning.

As explosion energy, and thus shock temperature, increases the isotopes are produced in greater quantity and farther out in the burning layers, particularly the He shell. Even with reduced shock temperatures in the 20 M$_{\odot}$ model we still see significant production in the Helium shell and destruction in the interior. The trend of outer-layer production increasing with explosion energy is also present in the 20 M$_{\odot}$ models, which tend to produce less over all. Thus we consider and to be suitable indicators of the supernova explosion energy.

We note also the double peak in the He shell production for both isotopes; the dip corresponds to the sudden drop in C, O, and Si abundances and an increase in He abundances in the progenitor. The inner and outer peak of this double feature are approximately the same in , but the outer peak shows an almost order of magnitude increase for . Thus, produces more in the outer regions of the burning layers than , which may provide with an observational advantage, as 