Precise study of the supernova reaction ⁴⁰Ca(α,γ) ⁴⁴Ti by activation and in-beam γ-spectroscopy

The radioactive nuclide ⁴⁴Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and very recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of ⁴⁴Ti should therefore be known with high precision. Over the last years there have been various studies of the ⁴⁰Ca(α,γ)⁴⁴Ti reaction, which is dominating the ⁴⁴Ti production in supernovae. Those studies have been performed using in-beam γ-spectroscopy, activation, accelerator mass spectrometry (AMS), and recoil mass spectrometry via inverse kinematics. However, there are still discrepancies in the resulting reaction rates. Using an α-beam of 1-2 A intensity the strengths of the strongest ⁴⁰Ca(α,γ)⁴⁴Ti resonances from 3.5 to 4.5 MeV laboratory α-energy have been studied by in-beam γ-counting and activation. The samples have been analyzed in the ultra-low-background underground γ-counting facility "Felsenkeller Dresden". The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA). An AMS measurement of the activated samples is in preparation.