F. M. Nunes

Solar fusion cross sections II: the pp chain and CNO cycles

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for {sup 8}B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

Core excitation in one neutron halo systems

Abstract Coupled channel calculations are performed for one neutron halo nuclei using a rotational model for the core structure. A deformed Woods-Saxon potential is used for the neutron-core interaction, where the deformation parameter is estimated using the quadrupole moment of the core and the charge to mass deformation ratio given by shell model calculations. Mean square radii and B (E1) transitions from the first excited state to the ground state in 11 Be are presented and good agreement with experiment is found. The same calculations were performed for 13 C but the agreement with experiment was not as good. Phase shifts for low energy neutrons on 10 Be and 12 C are calculated and we determine positions and widths of resonances. Predictions for the continuum only partly agree with the experimental spectrum. We also calculate the B (E1) distribution of 11 Be for transitions from the ground state to the continuum and these agree with recent coulomb dissociation data. Following the controversy generated by the experimental results for the ground state in 10 Li, we apply our method to investigate the structure of this nucleus.

Core excitation in three-body systems: Application to 12Be

Abstract Core excitation is included in the three-body hyperspherical formulation for systems of the type (core + n + n). We show that core excitation generates a three-body attraction, improving on the common underbinding problem present in many inert-core models. The Pauli principle significantly influences both the binding energies and the wave functions. A study of the effect of the different terms of the nn interaction on the three-body system is presented. The model is applied to 12Be, where one would expect that the inert-core approximation would not be appropriate. A deformed n-core interaction is determined by the properties of the subsystem 11Be. Results for the binding energy, r.m.s. radius, structure and momentum distribution of the ground state of 12Be are presented, and very good agreement with experimental data is found. A full comparison with the inert-core model is made. The results with core excitation show a very small component of ( p 1 2 )2 neutrons in the ground-state wave function, in contrast to the inert-core model where the 12Be ground state is mainly ( p 1 2 )2 neutrons relative to the core. We point out the possible implications of this fact for heavier Be isotopes, especially 13Be. The spectrum of 12Be bound excited states is calculated and compared with the measured values and some discrepancies are found. Following a recent proposal for an experiment, predictions for the 12Be(p,d) transfer cross sections are given.

Three-body description of direct nuclear reactions: Comparison with the continuum discretized coupled channels method

The continuum discretized coupled channels (CDCC) method is compared with the exact solution of the three-body Faddeev equations in momentum space. We present results for (i) elastic and breakup observables of d+{sup 12}C at E{sub d}=56 MeV (ii) elastic scattering of d+{sup 58}Ni at E{sub d}=80 MeV, and (iii) elastic, breakup, and transfer observables for {sup 11}Be+p at E{sub {sup 11}Be}/A=38.4 MeV. Our comparative studies show that in the first two cases, the CDCC method is a good approximation of the full three-body Faddeev solution, but for the {sup 11}Be exotic nucleus, depending on the observable or the kinematic regime, it may miss some of the dynamic three-body effects that appear through the explicit coupling to the transfer channel.

Halo Nucleus Be11: A Spectroscopic Study via Neutron Transfer

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct-reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus 11Be, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the 10Be d;p reaction has been used in inverse kinematics at four beam energies to study the structure of 11Be. The spectroscopic factors extracted using the adiabatic model were found to be consistent across the four measurements and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in an n j 2s1=2 state coupled to the ground state of 10Be is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p1=2 state.

Ultracold neutrons, quantum effects of gravity and the weak equivalence principle

We consider an extension of a recent experiment with ultracold neutrons and the quantization of their vertical motion in order to test the weak equivalence principle. We show that an improvement in the energy resolution of the experiment may allow us to establish a modest limit to the weak equivalence principle and the gravitational screening constant. We also discuss the influence on a possible new interaction of nature.

Testing the continuum-discretized coupled channels method for deuteron-induced reactions

The Continuum Discretized Coupled Channels (CDCC) method is a well established theory for direct nuclear reactions which includes breakup to all orders. Alternatively, the 3-body problem can be solved exactly within the Faddeev formalism which explicitly includes breakup and transfer channels to all orders. With the aim to understand how CDCC compares with the exact 3-body Faddeev formulation, we study deuteron induced reactions on: i)

Scaling and interference in the dissociation of halo nuclei

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Nuclear Theory and Science of the Facility for Rare Isotope Beams

Be at

Transfer to the continuum and breakup reactions

E_{\rm d}= 21.4, 40.9 \; {\rm and} \; 71