Article révisé par les pairs
Résumé : The 44Ti (t1/2 = 59 y) nuclide is considered an important signature of core-collapse supernova (SN) nucleosynthesis and has recently been observed as live radioactivity by γ-ray astronomy from the Cas A SN remnant. We investigated in the laboratory the major 44Ti production reaction 40Ca(α,γ)44Ti (E cm ∼ 0.6-1.2 MeV/u) by off-line counting of 44Ti nuclei using accelerator mass spectrometry. The observed yield is significantly higher than inferred from previous prompt γ-spectroscopy experiments. The present data are interpreted in terms of the BRUSLIB statistical model which incorporates a microscopic model of nuclear level densities and of the γ-ray strength function, and a global α-nucleus optical-model potential and confirm the strong suppression in yield expected for (α,γ) reactions on self-conjugate (N =Z) nuclei. The derived astrophysical rate of the 40Ca(α,γ)44Ti reaction is a factor 5-10 higher than calculated in current models. We will present results of stellar calculations in spherical hydrodynamics using this reaction rate, showing an increase of the calculated SN 44Ti yield by a factor ∼ 2 over current estimates. An increase by a factor of ∼ 2 in 44Ti is found also in the calculated fall back material. The yields calculated by multi-dimensional SN explosion calculations proposed to explain the observed 44Ti yield of Cas A, in which parts of deeper layers can be ejected while some of the outer layers fall back, are expected to be enhanced in 44Ti as well.

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