Halo Nucleus 11Li Research Articles

Breakup reactions of halo nuclei

Coulomb and nuclear breakup of halo nuclei have been studied at RIKEN. In this contribution, we focus on the cases of Coulomb breakup of the one-neutron halo nucleus 11Be at 69MeV/nucleon with a lead target and the nuclear breakup of 11Be at 67MeV/nucleon with a carbon target. In these studies, we have extracted the angular distributions of 10Be + n c.m. system (inelastic scattering) as well as the relative energy spectra. The angular distributions have been found very important to extract the pure E1 component in the breakup with Pb target, while it has been used to specify the angular momentum of two discrete levels observed for the breakup with C target. We also present preliminary results of Coulomb breakup of the two-neutron halo nucleus 11Li.

Coulomb and nuclear breakup of halo nuclei

Breakup Reactions have been experimentally investigated for the one neutron halo nucleus 11Be and the two neutron halo nucleus 11Li at about 70 MeV/nucleon at RIKEN. We here focus on the breakup with a Pb target, where the Coulomb breakup is dominant over nuclear breakup, and its soft E1 excitation has been a central issue. For 11Be, we present the energy spectra analyzed with the inelastic scattering angle. The selection at very forward angles has been used to extract the E1 strength, which is then applied to obtain the spectroscopic factor of the halo ground state. For 11Li, we have observed significant E1 strength at very low relative energies, which were missing in the previous measurements.

Beyond the core + n + n model for the neutron halo nucleus 11Li

A new model beyond the core + n + n model is discussed for two-neutron halo nucleus 11Li. In this model, pairing correlations among two halo neutrons and p-orbital neutrons in the 9Li core are taken into account as an important ingredient of the exotic binding mechanism. The 10L= 9Li+ n system, which is a subsystem of 9Li+ n+ n, is studied, and it is shown that the Pauli-blocking effect of pairing correlations of the 9Li-core cluster due to a p 1 2 - valence neutron brings about the degeneracy of the single particle energies of p 1 2 and s 1 2 orbitals. For 11Li, three-body coupled-channel calculations are performed, and it is shown that the results explain observed exotic properties of very small separation energy S 2 n , large matter radius and large amplitude of the s-orbital configuration.

Resonances and continuums in the three-body breakup of halo nuclei

We investigate the three-body Coulomb breakup reaction of two-neutron halo nuclei 11Li, where we adopt the extended three-body model of 11Li with paying attention to the pairing correlation of the nuclei. We also employ the complex scaling method (CSM) to solve the three-body unbound states of 11Li. From the results, we cannot find any dipole resonances, at least, having small decay widths. This means that the breakup strengrth is exhausted by the continuum states. We discuss which component of the continuum states in the three-body system determines the structure of the breakup strength such as the low energy enhancement observed in the experiments.

A setup for high-resolution isotope shift measurements on unstable lithium isotopes

We present a laser spectroscopic approach for measuring the charge radius of the halo nucleus 11Li and report on recent progress in the development of the experimental apparatus.

Systematic model calculations of the hyperfine structure in light and heavy ions

Systematic model calculations are performed for the magnetization distributions and the hyperfine structure (HFS) of light and heavy ions with a mass close to A ~ 6 208 235 to test the interplay of nuclear and atomic structure. A high-precision measurement of lithium-isotope shifts (IS) for suitable transition, combined with an accurate theoretical evaluation of the mass-shift contribution in the respective transition, can be used to determine the root-mean-square (rms) nuclear-charge radius of Li isotopes, particularly of the halo nucleus 11Li. An experiment of this type is currently underway at GSI in Darmstadt and ISOLDE at CERN. However, the field-shift contributions between the different isotopes can be evaluated using the results obtained for the charge radii, thus casting, with knowledge of the ratio of the HFS constants to the magnetic moments, new light on the IS theory. For heavy charged ions the calculated n-body magnetization distributions reproduce the HFS of hydrogen-like ions well if QED contributions are suppressed. Ab-initio calculations of the HFS of 209Bi80+ were performed to analyse this surprising result. Here, the boiling of the QED vacuum gives an important contribution to the HFS, thus modifying the theoretical results of other models. The investigations performed have initiated detailed studies of the structure of lithium-like ions heavier then bismuth, to obtain predictions for the experiments on uranium, which are proposed at PHELIX-XRL. PACS Nos.: 31.15Pf, 31.30Jv, 32.10Hq, 21.10GV, 21.10FT, 21.60-n, 21.60+n

Dipole excited states in 11Li with complex scaling

The 1 − excitations of the three-body halo nucleus 11Li are investigated. We use adiabatic hyperspherical expansion and solve the Faddeev equations in coordinate space. The method of complex scaling is used to compute the resonance states. The Pauli forbidden states occupied by core neutrons are excluded by constructing corresponding complex scaled phase equivalent two-body potentials. We use a recently derived neutron–core interaction consistent with known structure and reaction properties of 10Li and 11Li. The computed dipole excited states with J π =1/2 +, J π =3/2 +, and J π =5/2 + have energies ranging from 0.6 to 1.0 MeV and widths between 0.15 and 0.65 MeV. We investigate the dependence of the complex energies of these states on the 10Li spectrum. The finite spin-3/2 of the core and the resulting core–neutron spin–spin interaction are important. The connection with Coulomb dissociation experiments is discussed and a need for better measurements is pointed out.

Local realizations of contact interactions in two- and three-body problems

Mathematically rigorous theory of the two-body contact interaction in three dimension is reviewed. Local potential realizations of this proper contact interaction are given in terms of Poschl-Teller, exponential and square-well potentials. Three body calculation is carried out for the halo nucleus 11Li using adequately represented contact interaction.

Cross sections for Coulomb and nuclear breakup of three-body halo nuclei

All possible dissociation cross sections for the loosely bound three-body halo nuclei 6He (n+n+ α) and 11Li (n+n+ 9Li) are computed as functions of target and beam energy. Both Coulomb and nuclear interactions are included in the same theoretical framework. The measurements agree with the calculations for energies above 100 MeV/nucleon. The largest cross sections correspond to final states with zero or three particles for heavy and with two neutrons for light targets.

Break-up of neutron-halo nuclei by diffraction dissociation and shakeoff

The interplay of diffraction dissociation and nuclear shakeoff is considered in a schematic but still realistic model for the case of the break-up of halo nuclei on light targets. We demonstrate that the shakeoff effect, arising from the momentum imparted by the core diffraction, is small but still identifiable in the experimental data for the dissociation of the one- and two-neutron halo nuclei 11Be and 11Li.

Towards the determination of the charge radius of 11 Li by laser spectroscopy

Isotope shift measurements by means of laser resonance ionization spectroscopy are a unique tool to determine the charge radii of halo nuclei. The most prominent halo nucleus 11Li is at the same time the best accessible candidate for such studies. The experimental method to determine the charge radius of this exotic nucleus and first test results on 7Li will be presented in this paper.

Direct Experimental Evidence for Strong Admixture of Different Parity States in11Li

Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus 11Li incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the 10Li fragments gives access to the momentum distribution of the removed neutron in 11Li. From the shape of the distribution, the (1s1/2)2 contribution to the mixture of (1s1/2)2 and (0p1/2)2 components in the ground-state wave function was determined to be (45±10)%. The angular correlation between the knocked out neutron and the one from the decay of 10Li shows a skew distribution signaling interference of these two different parity states.Received 9 December 1998DOI:https://doi.org/10.1103/PhysRevLett.83.496©1999 American Physical Society

Ternary fission yields of 241Pu(n th,f)

Ternary events in the thermal neutron induced fission of 241Pu(n,f) were studied with the recoil separator LOHENGRIN at the high-flux reactor of the Institut Laue Langevin in Grenoble. Yields and energy distributions could be determined for most isotopes of the elements hydrogen to oxygen. Also several heavier nuclei up to 30Mg could be observed. Yields were measured for 42 isotopes, for further 17 isotopes upper limits could be deduced. For the first time the halo nuclei 11Li, 14Be and 19C were found in neutron induced fission with yields of some 10 −10 per fission.

Core-breakup reactions of the halo nuclei 11Be and 11Li: momentum distributions and shadow effects

The halo nuclei 11Be and 11Li have been studied in core-breakup reactions where the halo neutrons are expected to be released without a major distortion due to the reaction. The widths of the halo-neutron momentum distributions have been extracted in coincidence with He fragments, Γ = 32 ± 4 MeV/ c, and Li fragments, Γ = 42 ± 4 MeV/ c for 11Be and with He fragments, Γ = 42 ± 6 MeV/ c for 11Li. The 11Be breakup gives a very low neutron multiplicity of 0.38±0.09 which is a manifestation of the shadowing of the neutron in the core-breakup reaction. This value can be understood from a simple theoretical calculation, which also accounts for the observed transverse momentum widths at small angles.

Fragment-neutron correlations in peripheral fragmentation of halo nuclei

Studies of nuclei far off the line of stability are one of the main topics in nuclear structure physics. The search for states with spatially extended low-density matter distributions, so-called “halos”, found predominantly in light neutron-rich nuclei is of central importance. Halo-breakup experiments were performed in complete kinematics with relativistic secondary beams of energies of 0.2–0.4 GeV/u at GSl. For the examples of the two-neutron halo nuclei 6He and 11Li results of angular, energy and momentum correlation measurements after breakup into a core fragment and valence neutrons are given and single-particle ground-state properties and large low-lying multipole strength near the threshold for particle emission will be discussed.

Spectroscopy of the halo nucleus 11Li by an experimental study of 11Li+p collisions.

An experimental study of {sup 11}Li+{ital p} collisions at 75{ital A} MeV was performed. The excited state of {sup 11}Li at {ital E}{sup {asterisk}}=1.25{plus_minus}0.15 MeV was observed, which is a candidate for a neutron halo excitation. Four other {sup 11}Li states were manifested (at {approximately}3.0, 4.9, 6.4, and 11.3 MeV). Angular distributions were measured for elastic scattering {sup 11}Li+{ital p} and {sup 8}He+{ital p}. Structure of the {sup 11}Li halo was investigated using the eikonal approach. {copyright} {ital 1996 The American Physical Society.}

Electromagnetic dipole response of 11Li in a solvable three-body model

The electric dipole response of the halo nucleus 11Li is calculated in a hyperspherical three-body formulation, for an n− 9Li potential which has a low-lying s-wave virtual state. Strength concentrations at lower energies are found but no narrow resonances. There is close correspondence with MSU and RIKEN experimental data.

Study of halo nuclei with phenomenological relativistic mean field approach

Abstract The properties of halo nuclei are studied in the framework of the relativistic mean field approach. Single particle wave functions for last neutron configurations are obtained by using renormalized mean field potentials which reproduce experimental rms radii of halo nuclei. The extracted experimental density distributions and separation energies of loosely-bound neutrons of halo nuclei 11Li and 11Be are well described by the calculated results.

On Fusion Reactions Induced by 11Li via Soft Dipole Mode and Static Deformation

The numerical calculations for fusion reactions of a halo nucleus 11Li with deformed target nuclei at low energies have been carried out under the sudden limit for rotational excitation combined with a double folding potential of ion-ion interaction. The properties of fusion cross section involving the combined effects both from projectiles and target nuclei in such systems are investigated in detail.

Density distributions of halo nuclei

Density distributions of halo nuclei are studied by using a Hartree-Fock model with shell model occupation probabilities. Single-particle wave functions for the last neutron configuration are obtained by using renormalized mean field potentials of Skyrme interaction which reproduce small empirical separation energies of loosely-bound neutrons in halo nuclei. On the other hand, those for all other orbits are calculated from the original Hartree-Fock potential. Empirical density distributions of halo nuclei 11Be and 11Li are well described by the calculated densities not only in the surface region but also in the tail region 0442 beyond r=6 fm. This agreement validates the spherical shell model basis adopted, and also emphasizes the importance of the small separation energy effect for these halo nuclei.