Asymptotic normalization coefficients for14N+p15Oand the astrophysical

A. M. Mukhamedzhanov

¹

,

P. Bém

²

,

B. A. Brown

³

et al.

Abstract

The 14 N(p,␥) 15 O reaction, which controls energy production in the CNO cycle, has contributions from both resonance and direct captures to the ground and excited states. The overall normalization of the direct captures is defined by the corresponding asymptotic normalization coefficients ͑ANCs͒. Especially important is the ANC for the subthreshold state in 15 O at Ϫ0.504 keV since direct capture through this state dominates the reaction rate at stellar energies. In order to determine the ANCs for 14 Nϩp→ 15 O, the 14 N( 3 He,d) 15 O proton transfer reaction has been measured at an incident energy of 26.3 MeV. Angular distributions for proton transfer to the ground and five excited states were obtained. ANCs were then extracted from comparison to both distorted-wave Born approximation and coupled-channels Born approximation calculations. Using these ANCs, we calculated the astrophysical factor and reaction rates for 14 N(p,␥) 15 O. Our analysis favors a low value for the astrophysical factor.

Overlap functions, spectroscopic factors, and asymptotic normalization coefficients generated by a shell-model source term

“…For example, a correlated basis function theory [8] can account for short-range correlations, related to the strongly repulsive core of the nucleon-nucleon (NN) interaction. However, the SF reduction obtained within this theory for the closed-shell nuclei 16 O, 40 Ca, 48 Ca, and 208 Pb does not exceed 15%, which is inconsistent with experimental data. Long-range correlations, associated with quasiparticle excitations, can be taken into account within the self-consistent Green's function method [9].…”

“…Long-range correlations, associated with quasiparticle excitations, can be taken into account within the self-consistent Green's function method [9]. The SFs obtained within this method for 48 Ca and 56 Ni are in agreement with those obtained from (e,e p) and heavyion knockout experiments, thus showing that the long-range correlations in SF reduction are much more important than the short-range ones. However, a more systematic application of this method to various closed-shell nuclei ranging from 16 O to 60 Ca shows that reduction factors cannot be smaller than 0.73 [10].…”

“…In many publications S exp and S th were often in reasonable agreement. It has been found, however, that proton SFs in the closed-shell nuclei 16 O, 40,48 Ca, and 208 Pb, obtained from (e,e p) reactions, the mechanism of which is much better understood than that of transfer reactions, are 50%-60% smaller than those expected from the independent-particle model [1]. A similar reduction of SFs has been found for other nuclei such as 7 Li, 12 C, 30 Si, 31 P, 51 V, and 90 Zr [2].…”

Low energy scattering cross section ratios ofN14(p,p)N14

“…Energies of subthreshold states were fixed at the values given in the compilation [20], ANCs are fixed to those given in Ref. [17] after changing from an (l, j) to an (s, l) coupling scheme. Uncertainties are of the form (statistical, systematic, model).…”

“…Of the seven possible γ ray transitions to bound states in 15 O, three are estimated to account for ≈90% of the total cross section at stellar energies, with the ground state transition accounting for between 15 and 30% of the total [5,10,11]. This transition is especially difficult to extrapolate because the E x = 6.79 MeV subthreshold state strongly interferes with other resonances and the direct capture process, as shown in Fig 2. Asymptotic normalization coefficients (ANC's) have been measured for the E x = 6.79 MeV state and others [17,18] as a way to constrain the contributions from direct capture and the tail of the 6.79-MeV state. However, the large uncertainty in the 6.79-MeV state's γ-width im- 15 O nucleus.…”