Shallow-underground study of the supernova reaction 40Ca(α,γ)44Ti and the Dresden Felsenkeller

The 40Ca(alpha,gamma)44Ti reaction dominates the production of the radionuclide 44Ti (half-life 58.9 years) in the alpha-rich freezeout phase of a supernova. As 44Ti is believed to be produced near the so-called mass cut between ejected and infalling material, its detection may help constrain supernova models. Satellite-based gamma observatories have reported 44Ti detections from one supernova remnant, giving a snapshot of current supernova activity. The main production reaction 40Ca(alpha,gamma)44Ti has been studied in the Felsenkeller shallow-underground laboratory by activation, and at the surface of the Earth by in-beam gamma-spectrometry. New values for the strengths of the resonances near 4.5 and 3.5 MeV have been determined, improving the precision of the astrophysical reaction rate at temperatures of 2.5 GK and above.