Threshold anomaly in non-central forces

The behaviour of the threshold anomaly for non-central potentials, which account for collective excitations in heavy-ion collisions, is investigated. It is shown that the non-central potentials should exhibit an energy dependence at energies in the vicinity of the Coulomb barrier. This energy dependence is, however, different from that of the elastic optical potential, occurring at lower energies. It if further shown that there are corrections to the traditional collective model such that, if the transition potential is expressed as the derivative of the optical potential, the corresponding deformation length will be complex and energy-dependent. Simple model calculations are presented.Dirección General de Investigaciones Científicas y Técnicas PB89-0636

Identifying structures in the continuum: Application to 16 Be

Background: The population and decay of two-nucleon resonances offer exciting new opportunities to explore dripline phenomena. A proper understanding of these systems requires a solid description of the three-body (core+N +N) continuum. The identification of a state with resonant character from the background of nonresonant continuum states in the same energy range poses a theoretical challenge. Purpose: Establish a robust theoretical framework to identify and characterize three-body resonances in a discrete basis, and apply the method to the two-neutron unbound system 16Be. Method: A resonance operator is proposed, which describes the sensitivity to changes in the potential. Resonances,understoodasnormalizablestatesdescribinglocalizedcontinuumstructures,areidentifiedfromthe eigenstates of the resonance operator with large negative eigenvalues. For this purpose, the resonance operator is diagonalizedinabasisofHamiltonianpseudostates,whichinthepresentworkarebuiltwithinthehyperspherical harmonics formalism using the analytical transformed harmonic oscillator basis. The energy and width of the resonance are determined from its time dependence. Results: The method is applied to 16Be in a 14Be+n+n model. An effective core+n potential, fitted to the available experimental information on the binary subsystem 15Be, is employed. The 0+ ground state resonance of 16Be presents a strong dineutron configuration. This favors the picture of a correlated two-neutron emission. Fitting the three body interaction to the experimental two-neutron separation energy |S2n|=1.35(10) MeV, the computed width is (0+)=0.16 MeV. From the same Hamiltonian, a 2+ resonance is also predicted with εr(2+)=2.42 MeV and (2+)=0.40 MeV. Conclusions: The dineutron configuration and the computed 0+ width are consistent with previous R-matrix calculationsforthetruethree-bodycontinuum.Theextractedvaluesoftheresonanceenergyandwidthconverge with the size of the pseudostate basis and are robust under changes in the basis parameters. This supports the reliability of the method in describing the properties of unbound core+N +N systems in a discrete basis.Spanish Ministerio de Ciencia, Innovación y Universidades, European Regional Development Fund (FEDER), (FIS2017-88410-P, FPA2016-77689-C2-1-R, FIS2014-51941-P )European Union’s Horizon 2020 (No. 654002

Reaction theory: status and perspectives

The current status of the reaction theory of nuclear collisions involving weakly-bound exotic nuclei is presented. The problem is addressed within the Continuum Discretized Coupled Channel (CDCC) framework, recalling its foundations and applications, as well as its connection with the Faddeev formalism. Recent developments and improvements of the method, such as core and target excitations and the extension to three-body projectiles, are presented. The use of the CDCC wave function in the calculation of inclusive breakup reactions is also introduce

Three-body continuum-discretized coupled-channel calculations for 6 He scattering from heavy nuclei

ata for scattering of 6He from 197Au, 208Pb, and 209Bi targets at low energies were consistently analyzed by use of the continuum-discretized coupled-channels method and the dineutron model of the projectile. A very good description of the experimental data was obtained with the strength of the dipole couplings reduced by 50%. We find that the dipole couplings are responsible for the suppression of the Coulomb rainbow and that the quadrupole couplings must be included in the calculations in order to obtain good agreement with the elastic-scattering data at more backward angles.Ministerio de Ciencia y Tecnología FPA2003-05958 FPA2005-0446

Core excitation effects in halo nuclei using a transformed oscillator basis

A recent generalization of the Transformed Harmonic Oscillator basis, intended to consider core excitations in the structure of one nucleon halo nuclei, is applied to the break up of 11Be. The reaction studied is 11Be+208Pb at 69 MeV/nucleon. The experimental set up is designed to ensure pure dipole Coulomb excitations. Making use of the Equivalent Photon Method and the electromagnetic transition probabilities obtained with the transformed oscillator basis, a relevant contribution of the quadrupole excitations of the core is found. The inclusion of core excitations is, therefore, necessary for the correct extraction of the dipole electromagnetic transition probability of halo nuclei.Ministerio de Ciencia e Innovación FIS2011-28738-c02-01, FPA2009- 07653, FPA2009-08848, CSD2007-00042Junta de Andalucía FQM160, P07-FQM-0289

Stabilization method in two-body systems with core excitations

The validity of the stabilization method in core+valence systems including the possibility of exciting the core is studied. A pseudostate method, based on the transformed harmonic oscillator basis, is extended to include the core degrees of freedom. The method is applied to the case of 11Be structure considering the 0+ ground state and the 2+ first excited state of the 10Be core. The stabilization method is defined in terms of one parameter that can be chosen either discrete or continuous. In the application to 11Be, both cases are analyzed.Ministerio de Ciencia e Innovación FIS2011-28738-c02-01, FPA2009-07653, FPA2009-08848, CSD2007-00042Junta de Andalucía FQM160, P07-FQM-0289

Determining astrophysical three-body radiative capture reaction rates from inclusive Coulomb break-up measurements

A relationship between the Coulomb inclusive break-up probability and the radiative capture reaction rate for weakly bound three-body systems is established. This direct link provides a robust procedure to estimate the reaction rate for nuclei of astrophysical interest by measuring inclusive break-up processes at different energies and angles. This might be an advantageous alternative to the determination of reaction rates from the measurement of B(E1) distributions through exclusive Coulomb break-up experiments. In addition, it provides a reference to assess the validity of different theoretical approaches that have been used to calculate reaction rates. The procedure is applied to Li11 (Li9+n+n) and He6 (He4+n+n) three-body systems for which some data exist.This work has been partially supported by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (FEDER) under Projects No. FIS2011-28738-c02-01, No. FIS2013-41994-P, No. FPA2013-47327- C2-1-R, No. FIS2014-53448-c2-1-P, and FIS2014-51941-P and by Junta de Andalucía under Group No. FQM-160 and Project No. P11-FQM-7632. J. Casal acknowledges support from the Ministerio de Educacion, Cultura y Deporte, FPU Research Grant No. AP2010-3124. M. Rodríguez-Gallardo acknowledges postdoctoral support from the Universidad de Sevilla under the V Plan Propio de Investigacion, Contract No. USE-11206-M.Peer Reviewe

Elastic Scattering of 6He on Heavy Targets at Coulomb Barrier Energies

Elastic cross sections for the scattering of 6He projectiles by 208Pb at 27 MeV have been studied. The data have been analyzed within the framework of the Optical Model using Saxon–Woods phenomenological form factors for both the real and imaginary parts of the nuclear potential. The elastic scattering data suggests the presence of a long range absorption mechanisms which might be related to the halo structure of 6He.Ministerio Ciencia y Tecnología FPA2002-04181- C04-04 y FPA2000-1592-C03-0

Reorientation and coupling effects in polarized heavy ion fusion

A simple model to understand the reaction mechanisms in the fusion of polarized heavy ions based on tidal symmetry, the sudden approximation and barrier penetration is presented. The model is applied to 23Na+208Pb. The effect of the ground state reorientation and the coupling to rotational states is studied. Enhancement of the sub-barrier fusion cross sections and the fusion J-moments just above the barrier are found. The polarization of the projectile affects strongly the fusion around and below the Coulomb barrier.Dirección General de Investigaciones Científicas y Técnicas PB89-063

Configuration localized Morse wave functions: Application to vibrational transitions in anharmonic diatomic molecules

The bound states of a Morse potential are described in terms of a basis of states that are characterized for being eigenstates of the Morse variable. These states are strongly localized in configuration space; thus they are called configuration localized Morse (CLM) wave functions. These are shown to provide a powerful tool to calculate analytically, to a good approximation, matrix elements of arbitrary functions of the interatomic separation between vibrational states of anharmonic diatomic molecules. Applications of CLM wave functions to the calculation of vibrational transitions in HF and DF diatomic molecules are presented.Dirección General de Investigación Científica y Técnica PB95-0533European Commission CI1*-CT94-007