First direct limit on the 334 keV resonance strength in ^22 Ne( α , γ ) ^26 Mg reaction

In stars, the fusion of ^22 Ne and ^4 He may produce either ^25 Mg, with the emission of a neutron, or ^26 Mg and a γ ray. At high temperature, the ( α ,n ) channel dominates, while at low temperature, it is energetically hampered. The rate of its competitor, the ^22 Ne( α , γ ) ^26 Mg reaction, and, hence, the minimum temperature for the ( α ,n ) dominance, are controlled by many nuclear resonances. The strengths of these resonances have hitherto been studied only indirectly. The present work aims to directly measure the total strength of the resonance at E_r = 334 keV (corresponding to E_x = 10949 keV in ^26 Mg). The data reported here have been obtained using high intensity ^4 He ^+ beam from the INFN LUNA 400 kV underground accelerator, a windowless, recirculating, 99.9