Status of reaction theory for studying rare isotopes

Reactions are an important tool to study nuclear structure and for extracting reactions relevant for astrophysics. In this paper we focus on deuteron induced reactions which can provide information on neutron shell evolution as well as neutron capture cross sections. We review recent work on the systematic comparison of the continuum discretized coupled channel method, the adiabatic wave approximation and the Faddeev momentum-space approach. We also explore other aspects of the reaction mechanism and discuss in detail difficulties encountered in the calculations.Comment: 7 pages, 5 figures, proceeding for HITES 201

Connection between asymptotic normalization coefficients, subthreshold bound states, and resonances

Journals published by the American Physical Society can be found at http://publish.aps.org/We present here useful relations showing the connection between the asymptotic normalization coefficient (ANC) and the fitting parameters in K- and R-matrix theory methods which are often used when analyzing low energy experimental data. It is shown that the ANC of a subthreshold bound state defines thr normalization of both direct radiative capture leading to this state and resonance capture in which the start: behaves like a subthreshold resonance. A determination of the appropriate ANC(s) thus offers an alternative method for finding the strength of these types of capture reactions, both of which are important in nuclear astrophysics. [S0556-2813(99)01006-7]

Asymptotic normalization coefficients, spectroscopic factors, and direct radiative capture rates

Journals published by the American Physical Society can be found at http://publish.aps.org/We compare the use of asymptotic normalization coefficients (ANC's) and spectroscopic factors determined from peripheral transfer reactions for determining the overall normalization of peripheral direct radiative capture reaction processes. We demonstrate that ANC's provide a natural way to parametrize the rates of both peripheral transfer and direct capture reactions. Furthermore, ANC's inferred from one reaction may be used in the analysis of a second reaction without further knowledge regarding their origin, and independent measurements of a given ANC may be combined to give an overall "best value" in a straightforward manner. In contrast, a spectroscopic factor derived from analysis of a peripheral transfer reaction can only be used in subsequent calculations if one has detailed knowledge of the single-particle bound state orbital that was assumed when the spectroscopic factor was obtained

Radius of B-8 halo from the asymptotic normalization coefficient

Journals published by the American Physical Society can be found at http://publish.aps.org/The experimental asymptotic normalization coefficient determined from peripheral transfer reactions is used to obtain the root-mean-square radius of the wave function for the loosely bound proton in SB. It is shown that the asymptotic region contributes most and that matching of the interior wave function with the asymptotic part yields a nearly model-independent radius. We obtain [r(2)] (1/2) = 4.20 +/- 0.22 fm for the root-mean-square (rms) radius of the last proton, much larger than the rms radius of the Be-7 core. This large value and the fact that the asymptotic part of the proton wave function contributes 85% to the rms radius are good sign that B-8 is a halo nucleus

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

Elastic scattering of the proton drip-line nucleus F-17

Journals published by the American Physical Society can be found at http://publish.aps.org/Precision data have been obtained for the elastic scattering of F-17 on C-12 and N-14 at 10 MeV/nucleon to clarify the reaction mechanism for loosely bound nuclei at low energies and to assess the validity of a double-folding procedure to predict optical model potentials for use in indirect methods for nuclear astrophysics. The double-folding procedure incorporates density and energy-dependent effective nucleon-nucleon interactions with realistic densities consistent with experimentally determined asymptotic normalization coefficients. The derived potentials provide an excellent description of the data and point to a complete dominance of absorption at the barrier. A semiclassical analysis in terms of multireflection barrier-internal barrier series expansion of the scattering amplitude shows that only the barrier component survives in the scattering process, pointing to the peripheral character of the reactions