β-delayed α decay of ¹⁶N and the ¹²C (α,γ) ¹⁶O cross section at astrophysical energies: A new experimental approach

The ¹²C(α,γ)¹⁶O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for S_E1(300) and 7 to 120 keVb for S_E2(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi- elastic α scattering on ¹²C, α-transfer reactions to ¹⁶O, and 16N decay are usually included in the analysis. Here the β-delayed α decay of 16N is used to infer information on the ¹²C(α,γ)¹⁶O reaction and a new experimental technique is suggested.