Kirsebom, O. S.; Tengblad, O.; Lica, R.; Munch, M.; Riisager, K.; Fynbo, H. O. U.; Borge, M. J. G.; Madurga, M.; Marroquin, I.; Andreyev, A. N.; Berry, T. A.; Christensen, E. R.; Fernandez, P. Diaz; Doherty, D. T.; Van Duppen, P.; Fraile, L. M.; Gallardo, M. C.; Greenlees, P. T.; Harkness-Brennan, L. J.; Hubbard, N.; Huyse, M.; Jensen, J. H.; Johansson, H.; Jonson, B.; Judson, D. S.; Konki, J.; Lazarus, I.; Lund, M. V.; Marginean, N.; Marginean, R.; Perea, A.; Mihai, C.; Negret, A.; Page, R. D.; Pucknell, V.; Rahkila, P.; Sorlin, O.; Sotty, C.; Swartz, J. A.; Sorensen, H. B.; Toernqvist, H.; Vedia, V.; Warr, N.; De Witte, H.
(2018)
The C-12(alpha,gamma)O-16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced a width, gamma(11), of the bound 1(-) level in O-16 is particularly important to determine the cross section. The magnitude of gamma(11) is determined via sub-Coulomb a-transfer reactions or the beta-delayed a decay of N-16, but the latter approach is presently hampered by the lack of sufficiently precise data on the beta-decay branching ratios. Here we report improved branching ratios for the bound 1(-) level [b(beta,11) = (5.02 +/- 0.10) x 10(-2)] and for beta-delayed alpha emission [b(beta alpha) = (1.59 +/- 0.06) x 10(-5)]. Our value for b(beta alpha) is 33% larger than previously held, leading to a substantial increase in gamma(11). Our revised value for gamma(11) is in good agreement with the value obtained in a-transfer studies and the weighted average of the two gives a robust and precise determination of gamma(11), which provides significantly improved constraints on the C-12(alpha,gamma) cross section in the energy range relevant to hydrostatic He burning.