The β-delayed α spectrum of ^(16)N and the low-energy extrapolation of the ^(12)C(α, γ)^(16)O cross section

The low-energy part of the βα-decay spectrum of ^(16)N permits the determination of the reduced α-width θ^2_ɑ of the 7.12 MeV subthreshold state of ^(16)O, which dominates the low-energy p-wave capture amplitude of the astrophysically important reaction ^(12)C(α, γ)^(16)O. In a first run, a total of 7.1 x 10^3 a particles from the decay of ^(16)N nuclei, selected by the TRIUMF isotope separator TISOL, have been observed in a 10.6 μm detector in coincidence with the recoiling ^(12)C nuclei in a second detector, thus removing most sources of low-energy a background. These new data show a narrower width for the main a peak than previously determined. In addition, there is an indication of the low-energy interference anomaly predicted by several authors. The spectrum obtained can be parametrized in K- and R-matrix calculations, which also include the previously-measured ^(12)C(α, γ)^(16)O cross sections and elastic scattering phase shifts. Results of a data collection run in June with much higher α yields will be presented