THE BETA-DELAYED ALPHA SPECTRUM OF N-16 AND THE LOW-ENERGY EXTRAPOLATION OF THE C-12(ALPHA-GAMMA)O-16 CROSS-SECTION

The low-energy part of the betaalpha-decay spectrum of N-16 permits th e determination of the reduced alpha-width theta(alpha)2 of the 7.12 M eV subthreshold state of O-16, which dominates the low-energy p-wave c apture amplitude of the astrophysically important reaction C-12(alpha, gamma)O-16. In a first run, a total of 7.1 x 10(3) alpha particles fr om the decay of N-16 nuclei, selected by the TRIUMF isotope separator TISOL, have been observed in a 10.6 mum detector in coincidence with t he recoiling C-12 nuclei in a second detector, thus removing most sour ces of low-energy alpha background. These new data show a narrower wid th for the main alpha peak than previously determined. In addition, th ere is an indication of the low-energy interference anomaly predicted by several authors. The spectrum obtained can be parametrized in K- an d R-matrix calculations, which also include the previously-measured C- 12(alpha, gamma)O-16 cross sections and elastic scattering phase shift s. Results of a data collection run in June with much higher alpha yie lds will be presented.