40Ca(α,γ)44Ti and the production of 44Ti in supernovae

The nuclide ⁴⁴Ti is predicted to be produced in significant quantities in core-collapse supernovae, and indeed it has been observed in the supernova remnant Cassiopeia-A by space-based γ-ray telescopes. The main production of ⁴⁴Ti takes place in the α-rich freeze-out phase deep inside the supernova. The key reactions governing the ⁴⁴Ti abundance have been identified in an earlier sensitivity study. Using the recoil mass spectrometer DRAGON at the TRIUMF-ISAC facility in Vancouver, Canada, we measured the main production reaction ⁴⁰Ca(α,γ)⁴⁴Ti, resulting in an increased reaction rate compared to the rate derived from previous prompt γ-ray studies, which is commonly used in supernova models. The uncertainty of the ⁴⁴Ti production is now dominated by the rate of reactions with short-lived nuclides around ⁴⁴Ti, namely ⁴⁵V(p,γ)⁴⁶Cr, ⁴⁴Ti(α,p)⁴⁷V and ⁴⁴Ti(α,γ)⁴⁸Cr. The sensitivity of these reactions on the ⁴⁴Ti production has been revisited.