Ne-22(alpha,n)Mg-25: The key neutron source in massive stars - art. no. 202501

The excitation function of the reaction Ne-22(alpha, n)Mg-25, the key neutr on source in the astrophysical s process in massive stars, has been determi ned from threshold at E-alpha = 570 up to 1450 keV with an experimental sen sitivity of 10(-11) b. For all resonances in this energy range new resonanc e parameters have been measured. For a possible resonance at about 635 keV a new upper limit omega gamma < 60 neV for the strength was obtained. Based on the new data, improved reaction rates were calculated as a function of temperature. The new uncertainty limits are considerably smaller than in pr evious determinations, ruling out the large enhancement factors, up to 500, assumed in some stellar model calculations.