2010ApJ...715.1383H

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(α, γ)⁴⁴Ti reaction at E_α= 4.13, 4.54, and 5.36 MeV using γ-ray spectroscopy. At the highest beam energy, we also performed an activation measurement which 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 α-rich freezeout. Special attention has been paid to assessing realistic uncertainties of stellar reaction rates produced from a combination of experimental and theoretical cross sections. With such methods, we also develop a re-evaluation of the ⁴⁴Ti(α, p)⁴⁷V reaction rate. Using these two rates 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.