Abstract

The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 M ⊙ star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22 Ne (α, n) 25 Mg neutron producing reaction. The latter indeed has a direct impact on the distribution of the s-process seeds for the p-process. 1. THE P-PROCESS IN TYPE II SUPERNOVAE The most successful p-process models available to-date call for the synthesis of the stable neutron-deficient nuclides heavier than Fe (p-nuclei) in the O/Ne layers of Type II supernovae (SNII) ([13], hereafter RAHPN). Extensive calculations have been performed in RAHPN on the basis of stellar models which follow the evolution of helium stars from the beginning of helium burning up to, and including, the supernova explosion [10]. SNII explosions have been considered for stars with (approximately) 13, 15, 20 and 25 M ⊙ main sequence masses. The p-nuclei are produced in layers with explosion temperatures peaking in the (1.8-3.3)×10 9 K range, referred to as the P-Process Layers (PPLs). For each stellar mass we characterize the abundance of a p-nucleus i by its mean overproduction factor 〈Fi 〉 = 〈Xi 〉 /Xi,⊙, Xi, ⊙ being its solar mass fraction [1], and