We evaluate two dominant nuclear reaction rates and their uncertainties that
affect 44Ti production in explosive nucleosynthesis. Experimentally we develop
thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at E(alpha) = 4.13,
4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we
also performed an activation measurement that agrees with the thick target
result. From the measured yields a stellar reaction rate was developed that is
smaller than current statistical-model calculations and recent experimental
results, which would suggest lower 44Ti production in scenarios for the
alpha-rich freeze out. Special attention has been paid to assessing realistic
uncertainties of stellar rates produced from a combination of experimental and
theoretical cross sections, which we use to develop a re-evaluation of the
44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity survey
of 44Ti synthesis in eight expansions representing peak temperature and density
conditions drawn from a suite of recent supernova explosion models. Our results
suggest that the current uncertainty in these two reaction rates could lead to
as large an uncertainty in 44Ti synthesis as that produced by different
treatments of stellar physics.Comment: Comments: 45 pages, 19 postscript figures Minor corrections from
Referee and Proof Editors Figs 9 & 10 now in colo