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I investigate the Li11(p,t)Li9 two-neutron transfer reaction at Elab=33 MeV within the distorted wave Born approximation (DWBA). The Li11 and H3 nuclei are described in the hyperspherical formalism, as Li9+n+n and p+n+n configurations, respectively. The calculation of the cross section is shown to be much more complicated than in one-neutron transfer reactions, owing to the three-body structure of Li11. The Li11+p and Li9+t scattering wave functions are determined with the continuum discretized coupled channel (CDCC) method. Approximations derived from equivalent local potentials are used to compute the transfer cross section at the DWBA. The model reproduces experimental data reasonably well, considering that there is no adjustable parameter. I show that the cross section is fairly sensitive to the long-range part of the Li11 wave function, and therefore to its halo structure., SCOPUS: ar.j, info:eu-repo/semantics/published

We develop a four-body CDCC (continuum discretized coupled channel) model, aimed at describing reactions where both nuclei present a low breakup threshold. The only inputs are the interactions describing the colliding nuclei, and the four optical potentials between the fragments. The method is applied to the (formula presented) and (formula presented) systems. We show that, in general, breakup channels are crucial to reproduce the elastic cross sections. We suggest that the present wave functions could be used in future DWBA calculations., SCOPUS: cp.p, info:eu-repo/semantics/published

Background: Given the established 2α structure of Be8, a realistic model of four interacting α clusters must be used to obtain a Be8+Be8 interaction potential. Such a four-body problem poses a challenge for the determination of the Be8+Be8 optical potential (OP) that is still unknown due to the lack of the elastic Be8+Be8 scattering data. Purpose: To probe the complex Be8+Be8 optical potential in the coupled-reaction-channel (CRC) study of the α transfer C12(α,Be8) reaction measured at Eα=65 MeV and to obtain the spectroscopic information on the α+Be8 cluster configuration of C12. Method: The three- and four-body continuum-discretized coupled-channel (CDCC) methods are used to calculate the elastic α+Be8 and Be8+Be8 scattering at the energy around 16 MeV/nucleon, with the breakup effect taken into account explicitly. Based on the elastic cross section predicted by the CDCC calculation, the local equivalent OP's for these systems are deduced for the CRC study of the C12(α,Be8) reaction. Results: Using the CDCC-based OP's and α spectroscopic factors given by the cluster model calculation, a good CRC description of the α transfer data for both the Be8+Be8 and Be8+Be2+∗8 exit channels is obtained without any adjustment of the (complex) potential strength. Conclusion: The α+Be8 and Be8+Be8 interaction potential can be described by the three- and four-body CDCC methods, respectively, starting from a realistic α+α interaction. The α transfer C12(α,Be8) reaction should be further investigated not only to probe of the 4α interaction but also the cluster structure of C12., SCOPUS: ar.j, info:eu-repo/semantics/published

The Li11+p and Li11+d reactions are investigated in the continuum discretized coupled channel (CDCC) method with a three-body description (Li9+n+n) of Li11. I first discuss the properties of Li11, and focus on E1 transition probabilities to the continuum. The existence of a 1- resonance at low excitation energies is confirmed, but the associated E1 transition from the ground state does not have an isoscalar character, as suggested in a recent experiment. In a second step, I study the Li11+p elastic cross section at Elab=66 MeV in the CDCC framework. I obtain a fair agreement with experiment, and show that breakup effects are maximal at large angles. The breakup cross section is shown to be dominated by the 1- dipole state in Li11, but the role of this resonance is minor in elastic scattering. From CDCC equivalent Li11+p and Li11+n potentials, I explore the Li11+d cross section within a standard three-body Li11+(p+n) model. At small angles, the experimental cross section is close to the Rutherford scattering cross section, which is not supported by the CDCC. A five-body (Li9+n+n)+(p+n) calculation is then performed. Including breakup states in Li11 and in the deuteron represents a numerical challenge for theory, owing to the large number of channels. Although a full convergence could not be reached, the CDCC model tends to overestimate the data at small angles. I suggest that measurements of the Li9+p elastic scattering would be helpful to determine more accurate optical potentials. The current disagreement between experiment and theory on Li11+d scattering also deserves new experiments at other energies., SCOPUS: ar.j, info:eu-repo/semantics/published

We use a microscopic multicluster model to investigate the structure of $^{10}$Be and of $^{11}$Be. These nuclei are described by $\alpha+\alpha+n+n$ and $\alpha+\alpha+n+n+n$ configurations, respectively, within the Generator Coordinate Method (GCM). The 4- and 5-body models raise the problem of a large number of generator coordinates (6 for $^{10}$Be and 9 for $^{11}$Be), which requires specific treatment. We address this issue by using the Stochastic Variational Method (SVM), which is based on an optimal choice of the basis functions, generated randomly. The model provides good energy spectra for low-lying states of both nuclei. We also compute rms radii and densities, as well as electromagnetic transition probabilities. We analyze the structure of $^{10}$Be and of $^{11}$Be by considering energy curves, where one of the generator coordinates is fixed during the minimization procedure.

We apply a microscopic version of the Continuum Discretized Coupled Channel (CDCC) method, referred to as MCDCC, to 8Li and 8B scattering on different targets. The 8Li and 8B nuclei are described in a microscopic three-cluster model (α+ t+ n and α+ 3He + p), using the hyperspherical coordinates. We first present spectroscopic properties of these nuclei. Then, we determine 8Li + nucleus and 8B + nucleus potentials by using proton+ target and neutron+ target interactions. We compute various elastic-scattering cross sections and confirm that breakup effects are important, in particular at low energies. In general, we find a fair agreement with experiment, except for 8B+58Ni where we suggest that the data might be overestimated., SCOPUS: ar.j, info:eu-repo/semantics/published

The β-decay process of the He6 halo nucleus into the α+d continuum is studied in an updated three-body model. The He6 nucleus is described as an α+n+n system in hyperspherical coordinates on a Lagrange mesh. The shape and absolute values of the transition probability per time and energy units of new experiments are reproduced with a modified α+d potential. The obtained total transition probabilities are (2.48±0.16)×10-6s-1 for the full energy region and (2.40±0.16)×10-6s-1 for the cut-off E>150 keV. The strong cancellation between the internal and halo parts of the β decay matrix element is a challenge for future ab initio calculations., SCOPUS: ar.j, info:eu-repo/semantics/published

Primordial or big bang nucleosynthesis (BBN) is one of the three historical strong evidences for the big bang model. Standard BBN is now a parameter free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background (CMB) radiation. There is a good agreement between the primordial abundances of 4He, D, 3He and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D/H, to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we re-evaluates the D(p,g)3He, D(d,n)3He and D(d,p)3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S-factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D/H = (2.45$\pm0.10)\times10^{-5}$ (2$\sigma$), in agreement with observations.

We investigate the effect of a variation of fundamental constants on primordial element production in big bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (Li-5 and He-5) and A=8 (Be-8) unstable nuclei and complement earlier work on its effect on the binding energy of deuterium. The reaction rates for He3(d,p)He4 and H3(d,n)He4 are dominated by the properties of broad analog resonances in He-5 and Li-5 compound nuclei respectively. While the triple alpha process is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if Be-8 were stable during BBN. The nuclear properties (resonance energies in He-5 and Li-5 nuclei, and the binding energies of Be-8 and D) are all computed in a consistent way using a microscopic cluster model. The n(p,gamma)d, He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates are subsequently calculated as a function of the nucleon-nucleon interaction that can be related to the fundamental constants. We found that the effect of the variation of constants on the He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates is not sufficient to induce a significant effect on BBN, even if Be-8 was stable. In particular, no significant production of carbon by the triple alpha reaction is found when compared to standard BBN. We also update our previous analysis on the effect of a variation of constants on the n(p,gamma)d reaction rate., 14 pages, 12 figures

Dissociation has become an essential tool in several domains of nuclear physics. It provides useful information about the structure of halo nuclei, and Coulomb breakup can be used as an indirect method to measure radiative-capture cross sections at stellar energies. Though simple it may seem, this indirect technique relies on peculiar assumptions. Recent theoretical analyses of the Coulomb breakup of 8B have shown that these assumptions are not all satisfied. Whereas many experimental investigations on such a phenomenon have been conducted on 8B, the case of 17F has been poorly addressed up to now. An exclusive study of 17F breakup reactions has thus been performed at the FRIBs facility of the Laboratori Nazionali del Sud, Catania (Italy). The experimental setup and the detector systems allowed the measurement, event-by-event, of the X-Y coordinates of the interaction point on the target as well as the momenta and angles of all outgoing decay particles with a geometrical efficiency of 72% and a resolution of approximately 300 keV. The first results and preliminary model comparison are reported., info:eu-repo/semantics/published

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Antisymmetric + 14Cg.s. and + 14C(21+) wave functions are used in the generator coordinate formalism to investigate molecular properties of O18 states. Quadrupole moments, rms radii, and reduced widths of these states are calculated as well as reduced E1 and E2 transition probabilities between them. A number of molecular bands are found and analyzed. The assignment of experimental states to these bands is discussed. The alternating-parity band proposed by Gai et al. is interpreted as a fortuitous alignment of molecular states belonging to different bands. © 1985 The American Physical Society., info:eu-repo/semantics/published

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The generator-coordinate method is applied to the study of the three-+-particle system. The choice of the basis functions allows us to calculate the ++ 8Be phase shifts. We perform a comparison between the full three-cluster approach and two of its approximations. Distortion effects are shown to be important in the spectroscopic properties of C12. We present the Be8(+,) 12C S factor derived in the three-+-particle model. At low temperatures, the reaction rate is found to be slightly different from earlier studies. © 1987 The American Physical Society., info:eu-repo/semantics/published

The E1 and E2 components of the C12() 16O S factor are investigated microscopically with a generator-coordinate calculation involving + 12Cg.s. + 12C(21+), p+ 15Ng.s. and n+ 15Og.s. configurations. The theoretical capture cross sections towards the ground state and excited states are in semiquantitative agreement with experiment. Simple corrections to the microscopic expressions lead to good agreement with experimental data. The corrected model provides an S factor of 0.24 MeV b at the astrophysically important energy 0.3 MeV. © 1987 The American Physical Society., info:eu-repo/semantics/published

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The 16O(α,γ)20Ne cross section is calculated with antisymmetric wave functions by the generator coordinate method. E1 and E2 gamma widths in the 01 + and 0- bands of 20Ne agree fairly withd experiment. At low energies, the non-resonant S-factor is found larger than usually assumed. The S-factor is also enhanced by broad resonances of the 04 + band. © 1983., SCOPUS: ar.j, info:eu-repo/semantics/published

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The 7Be(p, γ)8B reaction is investigated through a microscopic three-cluster model, using the generator coordinate method. The 7Be nucleus is described by an α +3He structure, projected on the 3 2- and 1 2- states of 7Be. The model is tested by the calculation of M1 transition probabilities in 8Li and 8B and of the 7Li(n, γ)8Li cross section. At zero energy, we find an S-factor S(0) = 0.030 keV·b, slightly larger than the currently accepted value. © 1988., SCOPUS: ar.j, info:eu-repo/semantics/published

The Be9 and B9 spectra are investigated in a microscopic three-cluster model, using the generator-coordinate method. Both nuclei are described by a Be8 core surrounded by a nucleon. We present the n+8Be and p+8Be phase shifts, and the electromagnetic transition probabilities in Be9. A good overall agreement is found with the available experimental data. We suggest spin assignments for different poorly known states. The energy of the (1/2+ first excited state in B9 is in excellent agreement with a recent experimental investigation. © 1989 The American Physical Society., info:eu-repo/semantics/published

The C13(α,n)16O and C13(α,α)13C reactions are investigated through the generator-coordinate method. Two bands with marked α+ 13C structure are found in the O17 spectrum. Experimental candidates are proposed. The microscopic C13(α,α)13C cross sections are in fair agreement with experimental data. We show that the C13(α,n)16O cross section at stellar energies is strongly affected by the 1/2 2+ (6.36 MeV) weakly bound state. The astrophysical S factor below Ec.m.=0.3 MeV is therefore significantly enhanced with respect to the extrapolations used for astrophysical purposes. © 1987 The American Physical Society., info:eu-repo/semantics/published

The recent results of Hahn et al. on the 16O(α,γ)20Ne capture reaction are discussed in the light of a microscopic calculation. We suggest that the S factor at 300 keV proposed by Hahn et al. should be substantially increased. © 1988 The American Physical Society., info:eu-repo/semantics/published

The Ne22 spectrum is investigated with microscopic wave functions defined in the generator-coordinate formalism. This nucleus is described in a three-cluster model, involving an O16 core surrounded by a dineutron and an particle. The O18 cluster is projected out on the 0+ and 2+ states. We propose a band structure of Ne22 with experimental candidates. The model suggests the existence of a 0+ band presenting a marked +18O cluster structure. We present the +18O(0+,2+) collision matrices, and discuss the resonance properties in the (18)18O scattering. Electromagnetic transition probabilities in the Ne22 nucleus are calculated. From the theoretical Coulomb shifts between the mirror Ne22 and Mg22 nuclei, we suggest spin assignments for different Mg22 states. The (18,)22Ne capture cross section is calculated, and is used for determining microscopically the nonresonant reaction rate. © 1988 The American Physical Society., info:eu-repo/semantics/published

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