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

Recent developments for the calculation of elastic and non-elastic breakup of weakly-bound nuclei

In this contribution, we review some recent theoretical advances for the calculation of breakup cross sections in reactions induced by weakly-bound nuclei.Ministerio de Economía y Competitividad FIS2013-41994-P, CSD2007-00042Junta de Andalucía FQM160, P07-FQM-02894European Commission 60037

Core excitation effects in the breakup of halo nuclei

The role of core excitation in the structure and dynamics of two-body halo nuclei is investigated. We present calculations for the resonant breakup of 11Be on protons at an incident energy of 63.7 MeV/nucleon, where core excitation effects were shown to be important. To describe the reaction, we use a recently developed extension of the DWBA formalism which incorporates these core excitation effects within the no-recoil approximation. The validity of the no-recoil approximation is also examined by comparing with DWBA calculations which take into account core recoil. In addition, calculations with two different continuum representations are presented and compared.Ministerio de Ciencia e Innovación FIS2011-28738-c02-01, FPA2009- 07653, FPA2009-08848, CSD2007-00042Junta de Andalucía FQM160, P07-FQM-0289

Determining B(E1) distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to 11Be

A novel method to extract the B(E1) strength of a weakly bound nucleus from experimental Coulomb dissociation data is proposed. The method makes use of continuum discretized coupled channels (CDCC) calculations, in which both nuclear and Coulomb forces are taken into account to all orders. This is a crucial advantage with respect to the standard procedure based on the Equivalent Photon Method (EPM) which does not properly take into account nuclear distortion, higher order coupling effects, or Coulomb- nuclear interference terms. The systematic and statistical uncertainties of this procedure are evaluated. The procedure is applied to the 11Be nucleus using two sets of available experimental data at different energies, for which seemingly incompatible B(E1) have been reported using the EPM. We show that the present procedure gives consistent B(E1) strengths, thus solving the aforementioned long-standing discrepancy between the two measurements

Clustering effects in the 6^6Li(p,3^3He)4^4He reaction at astrophysical energies

Background: The understanding of nuclear reactions between light nuclei at energies below the Coulomb barrier is important for several astrophysical processes, but their study poses experimental and theoretical challenges. At sufficiently low energies, the electrons surrounding the interacting ions affect the scattering process. Moreover, the clustered structure of some of these nuclei may play a relevant role on the reaction observables. Purpose: In this article, we focus on a theoretical investigation of the role of clustered configurations of $^6$Li in reactions of astrophysical interest. Methods: The $^6$Li(p,$^3$He)$^4$He reaction cross section is described considering both the direct transfer of a deuteron as a single point-like particle in Distorted Wave Born Approximation (DWBA), and the transfer of a neutron and a proton in second-order DWBA. A number of two- and three-cluster structure models for $^6$Li are compared. Results: Within the two-cluster structure model, we explore the impact of the deformed components in the $^6$Li wave-function on the reaction of interest. Within the three-cluster structure model, we gauge the degree of $\alpha$-d clustering and explicitly probe its role on specific features of the reaction cross section. We compare the energy trend of the astrophysical $S$ factor deduced in each case. Conclusions: Clustered $^6$Li configurations lead in general to a significant enhancement of the astrophysical factor in the energy region under study. This effect only originates from clustering, whereas static deformations of the ground-state configuration play a negligible role at very low energies

Particle motion in a deformed potential using a transformed oscillator basis

The quantum description of a particle moving in a deformed potential is investigated. A pseudostate (PS) basis is used to represent the states of the composite system. This PS basis is obtained by diagonalizing the system Hamiltonian in a family of square integrable functions. In this work the transformed harmonic oscillator (THO) functions, obtained from the solutions of the harmonic oscillator using a local scale transformation (LST), are used. The proposed method is applied to the 11Be nucleus, treated in a two-body model (10Be+n). Structure observables have been studied. Wave functions and energies obtained for the bound states and some low-lying resonances are compared with those obtained by direct integration of the Schrödinger equation. The dipole and quadrupole electric transition probabilities for the low-energy continuum have been calculated in the THO basis, and compared with the exact distributions obtained with the scattering states.Ministerio de Ciencia e Innovación y FEDER FIS2011-28738-c02-01 FPA2009-07653 FPA2009-08848Programa Consolider-Ingenio 2010 CSD2007-00042Junta de Andalucía FQM160 P07-FQM-0289

Theory of single-charge exchange heavy-ion reactions

The theory of heavy-ion single-charge exchange reactions is reformulated. In momentum space, the reaction amplitude factorizes into a product of projectile and target transition form factors, folded with the nucleon-nucleon isovector interaction. The multipole structure of the transition form factors is studied in detail for Fermi-type non-spin-flip and Gamow-Teller-type spin-flip transitions, also serving to establish the connection to nuclear β decay. The reaction kernel is evaluated for central and rank-2 tensor interactions. Initial- and final-state ion-ion elastic interactions are accounted for by a distortion coefficient. Since the ion-ion interactions are dominated by the imaginary part of the optical potentials, the distortion coefficients can be evaluated in the strong absorption limit. For a Gaussian potential form factor, the distortion coefficient is evaluated in closed form, revealing the relation to the total reaction cross section. It is shown that at small momentum transfer distortion effects reduce to a simple scaling factor, allowing us to define a reduced forward-angle cross section which is given by nuclear matrix elements of β decay type. Thus we introduce new unit cross sections, as those traditionally used with light projectiles for spectroscopic purposes, for heavy-ion charge-exchange reactions. Results are discussed for τ ± excitations of 18 O and 40 Ca , respectively. Spectral distributions of nuclear-charge-changing transitions are obtained by self-consistent Hartree-Fock-Bogolubov (HFB) and quasiparticle random phase approximation (QRPA) theory and compared to spectroscopic data. The interplay of nuclear structure and reaction dynamics is illustrated for the single-charge exchange (SCE) reaction 18 O + 40 Ca → 18 F + 40 K at T lab = 270 MeV, by performing full-scale numerical calculations of the SCE cross section. We also show that the latter compare rather well with the results obtained within the strong absorption limit, thus confirming the possibility to factorize the forward-angle cross section into intrinsic nuclear transition dynamics and reaction dynamics.Programa Horizonte 2020 de la Unión Europea.654002Ministerio de Ciencia, Innovación y Universidades de España y Fondos FEDER. FIS2017- 88410-

Importance of the single-particle continuum in BCS pairing with a pseudostate basis

In a recent work [arXiv:1510.03185] the use of the Transformed Harmonic Oscillator (THO) basis for the discretization of the singleparticle continuum into a Generalized Bardeen-Cooper-Schrieffer (BCS) formalism was proposed for the description of weakly bound nuclei. We make use of the flexibility of this formalism to study the evolution of the pairing when the nucleus becomes more and more weakly bound. Specifically we focus on the evolution of the occupation of the different partial waves in 22O when the Fermi level approaches zer