Asymptotic normalization coefficients from the (20)Ne((3)He, d)(21)Na reaction and astrophysical factor for (20)Ne(p,gamma)(21)Na

Journals published by the American Physical Society can be found at http://publish.aps.org/The (20)Ne(p,gamma)(21)Na reaction rate at stellar energies is dominated by capture to the ground state through the tail of a subthreshold resonance state at an excitation energy of 2425 keV in (21)Na. Both resonant and direct capture contribute to the reaction rate while direct captures to other bound states are negligible. The overall normalization of direct capture to the subthreshold state is determined by the asymptotic normalization coefficient (ANC). Simultaneously this ANC determines the proton partial width of the subthreshold resonance state. To determine the ANC, the (20)Ne((3)He,d)(21)Na proton transfer reaction has been measured, at an incident energy of 25.83 MeV. Angular distributions for proton transfer to the ground and first three excited states were measured, and ANCs were then extracted from comparison with distorted-wave Born approximation calculations. Using these ANCs, we calculated the astrophysical factor for (20)Ne(p,gamma)(21)Na. Our total astrophysical factor is S(0)=5900 +/- 1200 keV b. Our analysis confirms that only nonresonant and resonant captures through the subthreshold state are important

Determination of the direct capture contribution for N-13(p,gamma)O-14 from the O-14 -> N-13+p asymptotic normalization coefficient

Journals published by the American Physical Society can be found at http://publish.aps.org/N-13(p, gamma)O-14 is one of the key reactions which trigger the onset of the hot CNO cycle. This transition occurs when the proton capture rate on 13N is faster, due to increasing stellar temperature (greater than or equal to10(9) K), than the N-13 beta-decay rate. The rate of this reaction is dominated by the resonant capture through the first excited state of O-14 (E-r=0.528 MeV). However, through constructive interference, direct capture below the resonance makes a non-negligible contribution to the reaction rate. We have determined this direct contribution by measuring the asymptotic normalization coefficient for O-14 --> N-13+p. In our experiment, an 11.8 MeV/nucleon N-13 radioactive beam was used to study the N-14(N-13, O-14)C-13 peripheral transfer reaction, and the asymptotic normalization coefficient, (C-p1/2(14O))(2)=29.0+/-4.3 fm(-1), was extracted from the measured cross section. The radiative capture cross section was estimated using an R-matrix approach with the measured asymptotic normalization coefficient and the latest resonance parameters. We find the S factor for N-13(p, gamma)O-14 to be larger than previous estimates. Consequently, the transition from the cold to hot CNO cycle for novae would be controlled by the slowest proton capture reaction N-14(p, gamma)O-15