We report on a hybrid framework for the systematic study of nuclear reactions at low energy, focusing on applications that involve transfer or photonuclear processes, and the application of this framework to the analysis of the 14N(p,γ)15O reaction.

An update of the NACRE compilation [3] is presented. This new compilation, referred to as NACRE II, reports thermonuclear reaction rates for 34 charged-particle induced, two-body exoergic reactions on nuclides with mass number A<16, of which fifteen are particle-transfer reactions and the rest radiative capture reactions. When compared with NACRE, NACRE II features in particular (1) the addition to the experimental data collected in NACRE of those reported later, preferentially in the major journals of the field by early 2013, and (2) the adoption of potential models as the primary tool for extrapolation to very low energies of astrophysical S-factors, with a systematic evaluation of uncertainties.As in NACRE, the rates are presented in tabular form for temperatures in the 106≲T⩽1010K range. Along with the ‘adopted’ rates, their low and high limits are provided. The new rates are available in electronic form as part of the Brussels Library (BRUSLIB) of nuclear data. The NACRE II rates also supersede the previous NACRE rates in the Nuclear Network Generator (NETGEN) for astrophysics. [http://www.astro.ulb.ac.be/databases.html]

The experimental measurement of the C-12(alpha,gamma)O-16 reaction cross section is not feasible bellow a few MeV and so the determination of the S(E) factor at astrophysical energies (E-0=0.3 MeV) must be done through indirect methods. These should consider the level structure of O-16, namely the 1(-) and 2(+) resonances at 9.59 MeV and 9.85 MeV, that dominate the elastic and capture cross sections at the energies covered by experimental data, and the 1- and 2+ subthreshold states at 7.12 MeV and 6.92 MeV.

We include the t+h configuration in the Li-6 ground state, by solving a coupled reaction channel variational model, as superposition of ad and th configurations. C)ur semi-microscopic model uses phenomenological NN, alphaN and th potentials, with central, spin-orbit and tenser components where known. For the overlap vertex functions in the A=3 and A=4 subsystems we use empirical or VMC descriptions, and the relative motion wave functions in the two partitions are expanded in orthonormal bases with the coefficients treated variationally. We examine first the influence of the transfer couplings by showing the effects of d alpha configurations on t+h elastic scattering

Measurements of cross section, vector analyzing power A(y), and tensor analyzing powers A(zz) and A(xz) over the angular range 10 degrees less than or equal to theta(lab) less than or equal to 40 degrees have been performed at E(Li-6) = 34 MeV for the Ni-58((6)<(Li)over right arrow>, d)Zn-62 and Ca-40((6)<(Li)over right arrow>, d)Ti-44 reactions leading to the ground state and first excited state of both residual nuclei. The reactions an described by distorted-wave Born approximation calculations, assuming a direct alpha-particle transfer mechanism. The asymptotic D/S state ratio eta for the d + alpha relative wave function in Li-6 is determined. In this one-step analysis, the best fit to the tensor observables leads to a value of eta = +0.0003 +/- 0.0009. This value is in disagreement with most of the previous theoretical and empirical determinations of eta. An investigation of two-step reaction mechanisms is performed, allowing the J(pi) = 3(+), 2(+), and 1(+) states in Li-6 to contribute to the transfer reaction channel. Reasonable agreement is achieved with the cross section and vector analyzing power data for several possible two-step amplitudes. It is found that the fitted magnitude of eta increases with increasing two-step amplitude, giving eta = -0.0030 +/- 0.0022 for unit amplitude, therefore not changing significantly from our one-step result. [S0556-2813(99)00812-2].

We calculate the (p,gamma) capture to the 0(+) ground state of Be-8 by means of the E1 and M1 multipoles. Scattering states are obtained in a single-particle model using potentials that reproduce the elastic phase-shift of the Li-7+p system at low energies, and the Be-8 g.s. is considered to be a pure single-particle p(3/2) state outside a Li-7 core. Describing the M1 resonance with a spectroscopic factor alpha(M1)(2), we obtain for the extrapolated astrophysical S-factor and for the M1 contribution at E-lab = 0, values of S(0) = 0.27 keV-barn and sigma(M1)/sigma(TOT) = 3%.

We calculate the (p,γ) capture to the 0+ ground state of 8Be by means of the E1 and M1 multipoles. Scattering states are obtained in a single-particle model using potentials that reproduce the elastic phase-shift of the 7Li+p system at low energies, and the 8Be g.s. is considered to be a pure single-particle p3/2 state outside a 7Li core. Describing the M1 resonance with a spectroscopic factor αM12, we obtain for the extrapolated astrophysical S-factor and for the M1 contribution at Elab=0, values of S(0)=0.27 keV-barn and σM1/σTOT=3%.

To test the model dependence of the extracted asymptotic parameters, we reanalyze published (d,t), (d,He-3) (d,alpha), and (d,Li-6) reactions, comparing recent variational Monte Carlo (VMC) microscopic vertex form factors with those used previously. In the (d,t) reactions studied the tensor observables are found to be proportional to eta, in (d,He-3) and (d,alpha) transfers there is some sensitivity to the vertex shape, while for (d,Li-6) there is a strong shape dependence. Comparisons with data show that the D states in the three- and four-body VMC vertex functions are slightly too weak. In the(d,Li-6) reaction the polarization data are not reproduced, clearly indicating that the D-state components of the new Li-6 models are too strong. [S0556-2813(99)06605-4].

One way to quantify the D-state component of the wave function of a nucleus is by the quantity eta, the ratio of the D- and S-state asymptotic normalization constants. Analyses of the analyzing powers from transfer reactions induced by polarized ions have been useful for the determination of eta in the A = 2 - 4 systems. In an effort to determine eta for the df ct relative motion in Li-6 we have measured analyzing powers for (Li-6,d) reactions on Ni-58 and Ca-40 at E(Li-6) = 34 MeV. The experiments were performed at Florida State University using the Optically Pumped Polarized Lithium Ion Source. We compared the data with the results of well-constrained DWBA calculations assuming a direct alpha-particle transfer mechanism. With eta the only free parameter in the calculations, a best fit to the tensor analyzing power data results in an average value of eta = +0.0003 +/- 0.0009, much smaller than previous determinations.

The asymptotic $D$- to $S$-state ratio $\ensuremath{\eta}$ for the $〈d\ensuremath{\alpha}|{}^{6}\mathrm{Li}〉$ bound-state overlap is determined from measurements of the tensor analyzing powers for ( ${}^{6}\stackrel{\ensuremath{\rightarrow}}{\mathrm{Li}},d$) reactions on medium-heavy targets. The reactions are described by the distorted-wave Born approximation assuming a direct $\ensuremath{\alpha}$-particle transfer reaction mechanism. The calculations provide good agreement with cross section and vector analyzing power data. A best fit to the tensor analyzing power data results in a new value of $\ensuremath{\eta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}+0.0003\ifmmode\pm\else\textpm\fi{}0.0009$, much smaller than previous experimental and theoretical determinations.