Nucleosynthesis and Clump Formation in a Core-Collapse Supernova

High-resolution two-dimensional simulations were performed for the first 5 minutes of the evolution of a core-collapse supernova explosion in a 15 M_☉ blue supergiant progenitor. The computations start shortly after bounce and include neutrino-matter interactions by using a lightbulb approximation for the neutrinos and a treatment of the nucleosynthesis due to explosive silicon and oxygen burning. We find that newly formed iron-group elements are distributed throughout the inner half of the helium core by Rayleigh-Taylor instabilities at the (Ni + Si)/O and (C + O)/He interfaces, seeded by convective overturn during the early stages of the explosion. Fast-moving nickel mushrooms with velocities up to ~4000 km s^-1 are observed. This offers a natural explanation for the mixing required in light-curve and spectral synthesis studies of Type Ib explosions. A continuation of the calculations to later times, however, indicates that the iron velocities observed in SN 1987A cannot be reproduced because of a strong deceleration of the clumps in the dense shell left behind by the shock at the He/H interface.