J. Gómez-Camacho

Four-body continuum-discretized coupled-channels calculations using a transformed harmonic oscillator basis

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled-channels framework is used for the scattering calculations. The formalism is applied to different reactions, {sup 6}He+{sup 12}C at 229.8 MeV, {sup 6}He+{sup 64}Zn at 10 and 13.6 MeV, and {sup 6}He+{sup 208}Pb at 22 MeV, induced by the Borromean nucleus {sup 6}He. Both the Coulomb and nuclear interactions with a target are taken into account.

Long range absorption in the scattering of 6He on 208Pb and 197Au at 27 MeV

Quasi-elastic scattering of 6He at E_lab=27 MeV from 197Au has been measured in the angular range of 6-72 degrees in the laboratory system employing LEDA and LAMP detection systems. These data, along with previously analysed data of 6He + 208Pb at the same energy, are analyzed using Optical Model calculations. The role of Coulomb dipole polarizability has been investigated. Large imaginary diffuseness parameters are required to fit the data. This result is an evidence for long range absorption mechanisms in 6He induced reactions. Comment: 10 pages, 10 figures, minor corrections. To appear in Nucl. Phys. A

Dynamic polarization potential induced by dipole Coulomb excitation

Abstract A local L -independent polarization potential due to dipole Coulomb excitation is derived with the use of the semiclassical Coulomb excitation amplitudes. It is showed that an analytic form for the imaginary polarization potential can be obtained for arbitrary dipole excitation energy while the real polarization potential is related to the imaginary part through a dispersion relation. The relative importance of the real and imaginary parts of the polarization potential is illustrated for the case of the collision of 11 Li and 208 Pb at different projectile energies.

Improved di-neutron cluster model for He-6 scattering

The structure of the three-body Borromean nucleus {sup 6}He is approximated by a two-body di-neutron cluster model. The binding energy of the 2n-{alpha} system is determined to obtain a correct description of the 2n-{alpha} coordinate, as given by a realistic three-body model calculation. The model is applied to describe the breakup effects in elastic scattering of {sup 6}He on several targets, for which experimental data exist. We show that an adequate description of the di-neutron-core degree of freedom permits a fairly accurate description of the elastic scattering of {sup 6}He on different targets.

Four-body continuum-discretized coupled-channels calculations

The development of a continuum-bin scheme of discretization for three-body projectiles is necessary for studies of reactions of Borromean nuclei such as {sup 6}He within the continuum-discretized coupled-channels approach. Such a procedure, for constructing bin states on selected continuum energy intervals, is formulated and applied for the first time to reactions of a three-body projectile. The continuum representation uses the eigenchannel expansion of the three-body S matrix. The method is applied to the challenging case of the {sup 6}He+{sup 208}Pb reaction at 22 MeV, where an accurate treatment of both the Coulomb and the nuclear interactions with the target is necessary.

Proton-proton correlations observed in two-proton decay of 19Mg and 16Ne

Proton-proton correlations were observed for the two-proton decays of the ground states of 19 Mg and 16 Ne. The trajectories of the respective decay products, 17 Ne + p + p and 14 O + p + p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.

α-particle production in the scattering of 6He by 208Pb at energies around the Coulomb barrier

New experimental data from the scattering of 6He + 208Pb at energies around and below the Coulomb barrier are presented. The yield of breakup products coming from projectile fragmentation is dominated by a strong group of α particles. The energy and angular distribution of this group have been analyzed and compared with theoretical calculations. This analysis indicates that the α particles emitted at backward angles in this reaction are mainly due to two-neutron transfer to weakly bound states of the final nucleus.

An su(1, 1) dynamical algebra for the Morse potential

An su(1, 1) dynamical algebra to describe both the discrete and the continuum parts of the spectrum for the Morse potential is proposed. The space associated with this algebra is given in terms of a family of orthonormal functions {Φσn} characterized by the parameter σ. This set is constructed from polynomials which are orthogonal with respect to a weighting function related to a Morse ground state. An analysis of the associated algebra is investigated in detail. The functions are identified with Morse-like functions associated with different potential depths. We prove that for a particular choice of σ the discrete and the continuum parts of the spectrum decouple. The connection of this treatment with the supersymmetric quantum mechanics approach is established. A closed expression for the Mecke dipole moment function is obtained.

Probing additional dimensions in the universe with neutron experiments

We investigate the modifications of the gravitational force in the context of recent work on large supplementary dimensions and deduce a formula for the expected compactification radius for the n additional dimensions in the universe, as a function of the Planck and the electro‐weak scales. We argue that the correspondingly modified gravitational force gives rise to effects that, although very small, might be within the detection range of dedicated neutron scattering experiments. We discuss the characteristics of an experimental setup to observe these effects.

Dynamic polarization potential induced by dipole Coulomb excitation to break-up states in 11Li scattering

Abstract The polarization potential due to dipole Coulomb excitation to the continuum of break-up states is obtained. The real and imaginary parts of the polarization potential is evaluated for the collision of 11 Li and 208 Pb at different projectile energies. The potentials show a sharp energy dependence, characteristic of the threshold anomaly, at energies below 100 MeV. Scattering calculations show the importance of the polarization potential.