New Measurements for the Astrophysically Important ⁴⁰Ca(α,γ)⁴⁴Ti Reaction

The 40Ca(Ì_å±,γ)44Ti reaction is thought to be the main production method for the short-lived radionuclide, 44Ti (t1/2 = 58.9 Ìâå± 0.3 yr). Production in the Ì_å±-rich freeze-out zone of a core-collapse supernova makes 44Ti an important nuclide in the understanding of nucleosynthesis in explosive stellar environments. A new measurement of the 40Ca(Ì_å±,γ)44Ti reaction has been performed through two different experimental approaches. During this work, a new accelerator mass spectrometry (AMS) facility was developed and commissioned at the University of Notre Dame, primarily for the measurement of reaction cross-sections of astrophysical interest. Using this facility, a series of 44Ti activation measurements were performed with a 40Ca beam incident on a 4He gas target. The four discrete energy ranges over which the activations occurred all lie within the temperature range relevant for Ì_å±-rich freeze-out. Further to this, an excitation curve was measured over the energy range EÌ_å± = 4600 - 3000 keV, using Ì_å±-particles incident on a 40Ca target. The good agreement between these two results resulted in the successful commissioning of the AMS facility. The new reaction rates derived in this work results in an increased expected yield of 44Ti in proposed supernova environments (for example Cassiopeia A) by ~ 40 %, when compared to 1D supernova models using reaction rates based on previous prompt γ-ray studies .