出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：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 (Ecm ~ 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.
