Resonance triplet at E_α = 4.5 MeV in the ⁴⁰Ca(α,γ)⁴⁴Ti reaction

The ⁴⁰Ca(α,γ)⁴⁴Ti reaction is believed to be the main production channel for the radioactive nuclide ⁴⁴Ti in core-collapse supernovae. Radiation from decaying ⁴⁴Ti has been observed so far for two supernova remnants, and a precise knowledge of the ⁴⁴Ti production rate may help improve supernova models. The ⁴⁰Ca(α,γ)⁴⁴Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at E_α = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the counting, and by in-beam spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to ωγ = (0.92 ± 0.20), (6.2 ± 0.5), and (1.31 ± 0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5GK.