The {beta}-delayed {alpha}-spectrum of {sup 16}N and the astrophysical aspects of the {sup 12}C({alpha},{gamma}){sup 16}O reaction

Radiative alpha-capture by {sup 12}C is a key process occurring during the helium-burning phase in red giant stars, and its rate remains one of the most significant uncertainties in the nucleosynthetic calculations for massive stars. This is largely due to the lack of precise experimental information concerning the values of the reduced {alpha}-particle widths of the J{sup {pi}} = 1{sup {minus}} and 2{sup +} subthreshold states in {sup 16}O to which the higher-energy radiative capture data are only weakly sensitive. Of these two states, the reduced {alpha}-width of the E{sub x} = 7.12 MeV J{sup {pi}} = 1{sup {minus}} level has been predicted to have a considerable effect on the structure of the hitherto unmeasured low-energy region of the {beta}-delayed {alpha}-particle spectrum of {sup 16}N. Experiments using the TRIUMF isotope separator TISOL have been performed to measure this {alpha}-spectrum down to an energy of E{sub {alpha}} = 600 keV, utilizing a coincidence technique which also accounts completely for the detector response function. The {alpha}-spectrum, containing 10{sup 6} counts, has been incorporated into both R- and K-matrix analyses along with the previously measured {sup 12}C({alpha},{gamma}){sup 16}O cross section and the {sup 12}C + {alpha} elastic phase shifts to yield a much improved value for S{sub E1}(300) keV. In light of this new determination of S{sub E1}(300), the available radiative capture data and elastic scattering phase shifts are re-analyzed, along with {beta}-delayed {alpha}-spectrum of {sup 16}N in an attempt also to place improved limits on the S{sub E1}(300) contribution to the {sup 12}C({alpha},{gamma}){sup 16}O cross section