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 fo
r the neutrinos and a treatment of the nucleosynthesis due to explosive sil
icon 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 conv
ective overturn during the early stages of the explosion. Fast-moving nicke
l mushrooms with velocities up to similar to 4000 km s(-1) are observed. Th
is offers a natural explanation for the mixing required in light-curve and
spectral synthesis studies of Type Ib explosions. A continuation of the cal
culations to later times, however, indicates that the iron velocities obser
ved in SN 1987A cannot be reproduced because of a strong deceleration of th
e clumps in the dense shell left behind by the shock at the He/H interface.