Halo Nucleus 11Li Research Articles

Spherical, Axial, and Triaxial Symmetries in the Study of Halo Nuclei with Covariant Density Functional Theory

The halo phenomenon in exotic nuclei has long been an important frontier in nuclear physics research since its discovery in 1985. In parallel with the experimental progress in exploring halo nuclei, the covariant density functional theory has become one of the most successful tools for the microscopic study of halo nuclei. Based on spherical symmetry, the relativistic continuum Hartree–Bogoliubov theory describes the first halo nucleus 11Li self-consistently and predicts the giant halo phenomenon. Based on axial symmetry, the deformed relativistic Hartree–Bogoliubov theory in continuum has predicted axially deformed halo nuclei 42,44Mg and the shape decoupling effects therein. Based on triaxial symmetry, recently the triaxial relativistic Hartree–Bogoliubov theory in continuum has been developed and applied to explore halos in triaxially deformed nuclei. The theoretical frameworks of these models are presented, with the efficacy of exploiting symmetries highlighted. Selected applications to spherical, axially deformed, and triaxially deformed halo nuclei are introduced.

Reaction dynamics of exotic and stable weakly-bound nuclei using a four-body continuum-discretized coupled-channels formalism

Reactions induced by four weakly-bound nuclei on a lead target, at energies around the Coulomb barrier, are described using the same four-body continuum-discretized coupled-channels formalism. The nuclei considered are the halo nuclei 11Li and 6He, the stable nucleus 9Be and the proton-rich nucleus 10C. The differences and similarities on the reaction dynamics are addressed.

Sensitivity of core+n potential on configuration mixing in ground state of neutron-rich exotic nuclei

We study the configuration mixing in the ground state of the neutron-rich exotic nuclei. The results for weakly-bound two-neutron halo nuclei 11Li and 22C, and the two-neutron unbound nucleus 26O are reported. For the present study, we use a three-body (core + n + n) structure model developed for describing the two-neutron halo system by explicit coupling of unbound continuum states of the subsystem (core + n). We use a density-dependent contact-delta interaction to describe the neutron-neutron interaction and its strength is varied to fix the binding energy. We report the two-neutron correlations in the ground state of these systems.

Soft giant resonance in two neutron halo nucleus 11Li

Lithium-11 is a showcase of neutron halos and has been providing new insight to nuclear structure researches. Recently, an isoscalar resonance at low excitation energy ($ E_\mathrm{x} \sim 1$ MeV) has been confirmed by the development of a low-energy high-intensity beam of 11Li at TRIUMF. By inelastic scattering measurements $ (\mathrm{p}, \mathrm{p}^{\prime})$ and $ (\mathrm{d}, \mathrm{d}^{\prime})$ with inverse kinematics, the first excited state of 11Li has been studied in detail and an isoscalar nature of the transitions has been confirmed and a strong transition amplitude has been observed indicating the soft-resonance of 11Li. Those recent experimental results on the excitation of the soft resonance are described and then recent theoretical developments based on the four-body continuum-discretized coupled-channels 11Li + p system are presented together with a brief history of the resonance search in 11Li.

Di-neutron correlations and decay dynamics of nuclei near and beyond drip line

Possible experimental probes for the strong di-neutron correlations in halo nuclei 6He and 11Li are discussed in the Coulomb breakup reactions. We then study a nucleus beyond the drip line 26O through the direct two-neutron decay. The excited first 2+ state of 26O is also discussed. To this end, we use consistently a three-body model taking into account the coupling to the continuum. Calculated results are compared with the recent experimental data from RIBF (Radioactive Ion Beam Factory) in RIKEN.

Core Deformation in the Two-Neutron Halo Nucleus, 11Li by Using Faddeev Equation

The properties of the two-neutron halo nucleus 11Li are investigated. The calculations are performed using the Faddeev equation with core excitation and Woods-Saxon potential. The core has been deformed and allowed to be excited to first 2+ state. This model enables to include the excitation of core of the three bodies, while the other two particles remain inert. Also, it is particularly suitable for obtaining the bound states structure compositions and binding energies of light exotic nuclei considered as three-body systems, which given the three effective of two body interactions. Results were compared with experimental data and three-body model. The handling of 11Li with an excited core in a microscopic cluster model was more accurate than that with an inert core in the three-body model. The dependence of three-body system energy on the quadruple of the core was investigated, and the core has an oblate shape.

Mechanism of Coulomb breakup reactions of two-neutron halo nuclei 6He and 11Li

We investigate the three-body Coulomb breakup reactions of two-neutron halo nuclei and discuss the correlations of every binary subsystem such as of core-n and n-n by showing the invariant mass spectra. It is found that the final-state interactions of core-n and n-n binary subsystems dominantly determine the observed energy distributions of the breakup cross sections, such as the low-lying enhancements. Furthermore, we investigate the effects of the 9Li core excitations on the Coulomb breakup cross section of 11Li. It is shown that the integrated E1 strength at low energy region is reduced by ~ 15 % by the inclusion of the 9Li core excitations.

Two-proton decay of the 6Be ground state and the double isobaric analog of 11Li

Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay.

Coulomb Breakup Reactions of Two-Neutron Halo Nuclei 6He and 11Li Using Complex-Scaled Solutions of the Lippmann–Schwinger Equation

We investigate the three-body Coulomb breakup reactions of two-neutron halo nuclei and discuss the effect of binary subsystem correlations such as of core–n and n–n. We furthermore calculate the invariant mass spectra. It is found that the final-state interactions of core–n and n–n binary subsystems dominantly determine the observed structures of the breakup cross sections, such as the low-lying enhancements.

Scattering of the halo nucleus 11Li and its core 9Li on 208Pb at energies around the Coulomb barrier

The first measurement of the elastic scattering of the halo nucleus 11Li and its core 9Li on 208Pb at energies around the Coulomb barrier is presented. The 11Li reaction showed a large cross section for the breakup channel, even at energies well below the barrier. The analysis of the 11Li + 208Pb scattering data in terms of the continuum-discretized coupled-channel calculations indicates that the effect of the coupling to the breakup channels produces a strong suppression of the elastic cross section at energies above and below the barrier. This effect is mainly due to the strong Coulomb coupling to the dipole states in the low-lying continuum of 11Li.

MICROSCOPICAL ANALYSIS OF THE REACTION CROSS-SECTIONS OF 11Li+12C and 22C+12C ELASTIC SCATTERING

Total reaction cross-sections of the two neutron halo nuclei 11Li and 22C elastic scattering from 12C target at E = 30–1000 MeV/nucleon have been analyzed using the eikonal phase shift based, for the first time, on the semi-phenomenological nucleon density. The obtained results reasonably agree with those of previous theoretical calculations as well as the corresponding experimental data.

Electric dipole response of halo nuclei

Characteristic features of electric dipole transitions at low excitation energies (soft E1 excitation) for halo nuclei are presented. Energy spectra of soft E1 excitations in the one neutron halo nucleus 11Be and in the two neutron halo nucleus 11Li using the Coulomb breakup reactions are shown, which illustrate the mechanism of the soft E1 excitation in these cases. We also show recent experimental results on inclusive Coulomb breakup performed at the new-generation RI beam facility, RIBF, at RIKEN. There, we have obtained evidence for halo structure in the very neutron rich nucleus 31Ne, which is the heaviest halo ever known.

How to measure nuclear ground-state properties in simple systems such as 11Li or U91+?

Atomic spectroscopy yields key information on properties of ground and isomeric states via a determination of the hyperfine structure and isotope shift. In order to deduce precise nuclear moments and charge radii, the electromagnetic fields produced by the electrons at the site of the nucleus must be known with high accuracy. This is presently possible only for simple systems with very few electrons. This contribution describes two scenarios for such experiments: the determination of the charge radius of the neutron-rich isotopes 8,9Li and of the halo nucleus 11Li at the on-line isotope separators at GSI and TRIUMF and the Highly charged Ion TRAP (HITRAP) facility which is under construction at GSI. HITRAP will enable the determination of atomic and nuclear properties of highly charged ions such as isotopes of hydrogen-like uranium with very high accuracy. For this purpose novel experimental set-ups are being built up by the international HITRAP collaboration.

Pairing correlations and soft dipole excitations in nuclei on the neutron-drip line

Paring correlations and soft dipole excitations in weakly bound nuclei on the edge of neutrondrip line are studied by using a three-body model. A density-dependent contact interaction is employed to calculate the ground state of halo nuclei 6He and 11Li, as well as a skin nucleus 24O. Dipole excitations in these nuclei are also studied within the same model. We point out that the dineutron-type correlation plays a dominant role in the halo nuclei 6He and 11Li having the coupled spin of the two neutrons S = 0, while the correlation similar to the BCS type is important in 24O. Contributions of the spin S = 1 and S = 0 configurations are separately discussed in the low-energy dipole excitations. The calculated results are compared with recent experimental data of 6He and 11Li.

Coulomb Breakup of 11Li

A new kinematically complete measurement of the Coulomb breakup of twoneutron halo nucleus 11Li on a Pb target has revealed a strong soft-E1 transition strength peaking at Ex∼0.6 MeV. This soft E1 strength amounts to 1.42±0.18 e2fm2, corresponding to 4.5±0.6 Weisskopf units(W.u.). The observed B(E1) distribution has been found in excellent agreement with a three-body calculation with strong two-neutron correlation and final state interactions.

Observation of Strong Low-LyingE1Strength in the Two-Neutron Halo NucleusLi11

An exclusive measurement has been made of the Coulomb dissociation of the two-neutron halo nucleus 11Li at 70 MeV/nucleon at RIKEN. Strong low-energy (soft) E1 excitation is observed, peaked at about Ex = 0.6 MeV with B(E1) = 1.42(18) e2fm2 for Erel < or = 3 MeV, which was largely missed in previous measurements. This excitation represents the strongest E1 transition ever observed at such low excitation energies. The spectrum is reproduced well by a three-body model with a strong two-neutron correlation, which is further supported by the E1 non-energy-weighted cluster sum rule.

Coulomb breakup of the two-neutron halo nucleus 11Li

Coulomb breakup of the two-neutron halo nucleus 11Li has been investigated in a kinematically complete measurement of three-body breakup of 11Li on a Pb target at approximately 70 MeV/nucleon at RIKEN. Cross-talk events have been excluded without affecting the efficiency very much up to very low relative energy. The resultant preliminary B(E1) spectrum has revealed high (E1) strength at Erel (three-body relative energy) ∼0.3 MeV, which was missing in the previous measurements. This E1 strength with the help of the E1 cluster sum-rule indicates a significant neutron–neutron correlation in the ground state of 11Li.

Coulomb breakup and pairing excitation of the two-neutron halo nucleus 11Li

The Coulomb breakup and pairing excitation of the two-neutron halo nucleus 11Li with the cluster orbital shell model have been studied. For the excited resonances in 11Li, we use the complex scaling method. We get an excited solution of 3/2− in 11Li.

Efimov Effect in Nuclear Three-Body Resonance Decays

We investigate the effects of the nearly fulfilled Efimov conditions on the properties of three-body resonances. Using the hyper-spheric adiabatic expansion method we compute energy distributions of fragments in a three-body decay of a nuclear resonance. As a realistic example we investigate the 1- state in the halo nucleus 11Li within a three-body model 9Li + n +n model. Characteristic features appear as sharp peaks in the energy distributions. Their origin, as in the Efimov effect, is in the large two-body s-wave scattering lengths between the pairs of fragments.

Borromean nuclei and three-body resonances

The interconnection between the resonances and virtual states of a three-body system and the resonances and virtual states in its two-body subsystems is investigated using the Borromean halo nucleus 11Li as a realistic example. The three-body core + neutron + neutron model is used, where the neutron-core interaction is fixed to reproduce a given s-wave virtual state and a p-wave resonance. The neutron-neutron interaction is then multiplied by a factor which is progressively changed from 0 to 1 and the resulting trajectories of the three-body states in the complex energy plane are investigated.