Ground State Of 11Li Research Articles

Reaction studies with neutron-rich light nuclei at the upgraded SEC Device: Exploring the excited structure of 11Li

The 11Li nucleus is considered the best example of a two-neutron halo nucleus. While the structure of the ground state is well established there is still a significant debate regarding its excited states despite of the multiple experiments realised mainly from the excitation of the ground state of 11Li that is rather complex. We propose a novel approach, to directly feed the different excited states of 11Li by the (t,p) reaction as 9Li has a simpler structure. We will employ a 9Li beam produced at ISOLDE and post-accelerated by HIE-ISOLDE to energies of 7 MeV/u to impinge on a 3H-target located at the upgraded SEC station, this station contains a new particle detection set up: composed of 5 Si-particle telescopes in a pentagon configuration with end caps consisting of 2 CD Si detectors downstream and 1 CD upstream has been prepared to offer the maximum angular coverage and resolution. Geant4 Monte Carlo simulations with the efficiency of the setup is presented in the following proceeding.

Description of the 11Li(p,d)10Li transfer reaction using structure overlaps from a full three-body model

Recent data on the differential angular distribution for the transfer reaction 11Li(p,d)10Li at E/A=5.7 MeV in inverse kinematics are analyzed within the DWBA reaction framework, using the overlap functions calculated within a three-body model of 11Li. The weight of the different 10Li configurations in the system's ground state is obtained from the structure calculations unambiguously. The effect of the 9Li spin in the calculated observables is also investigated. We find that, although all the considered models succeed in reproducing the shape of the data, the magnitude is very sensitive to the content of p1/2 wave in the 11Li ground-state wave function. Among the considered models, the best agreement with the data is obtained when the 11Li ground state contains a ∼31% of p1/2 wave in the n–9Li subsystem. Although this model takes into account explicitly the splitting of the 1+ and 2+ resonances due to the coupling of the p1/2 wave to the 3/2− spin of the core, a similar degree of agreement can be achieved with a model in which the 9Li spin is ignored, provided that it contains a similar p-wave content.

Distorted-wave Born approximation study of the 11Li(p,t)9Li reaction

The reaction 11Li(p,t)9Li(gs) at an incident energy of 4 MeV is treated in terms of a simplistic distorted-wave Born approximation transfer. The halo neutrons involved in the reaction are treated as a di-neutron cluster transferred in a simultaneous process. This appears to be a good approximation of the mechanism. The dominant contribution to the reaction comes from the known (1s1/2)2 structure component of the ground state of 11Li, and the cross section angular distribution seems to be relatively insensitive to the fact that 11 Li has an anomalously large radius due to its Borromean halo properties. Significantly this simple treatment of the reaction is in much better agreement with the experimental angular distribution than a more sophisticated calculation.

Investigation of the role of 10Li resonances in the halo structure of 11Li through the Li11(p,d)Li10 transfer reaction

Abstract The first measurement of the one-neutron transfer reaction 11Li(p,d)10Li performed using the IRIS facility at TRIUMF with a 5.7 A MeV 11Li beam interacting with a solid H2 target is reported. The 10Li residue was populated strongly as a resonance peak with energy E r = 0.62 ± 0.04 MeV having a total width Γ = 0.33 ± 0.07 MeV . The angular distribution of this resonance is characterized by neutron occupying the 1 p 1 / 2 orbital. A DWBA analysis yields a spectroscopic factor of 0.67 ± 0.12 for p 1 / 2 removal strength from the ground state of 11Li to the region of the peak.

Nuclear field theory predictions for 11Li and 12Be: Shedding light on the origin of pairing in nuclei

Recent data resulting from studies of two-nucleon transfer reaction on 11Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of 9Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived 11Li nucleus. In other words, the ground state of 11Li can be viewed as a neutron Cooper pair bound to the 9Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon-nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with (t, p) data on 7Li, suggest the existence of a pairing vibrational band based on 9Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of 11Li(p, t)9Li reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the N = 6 shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections σabs associated with the reactions 12Be(p, t)10Be(g.s.) and 12Be(p, t)10Be(pv) (≈10Be(p, t)8Be(g.s.)). In particular, concerning this last reaction, predictions of σabs can change by an order of magnitude depending on whether the halo properties associated with the d5/2 orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not.

11Li structure from experimental data

An analytical wave function for the 11Li ground state is constructed in a three-body Li 9 + n + n approach. Its parameters are fixed from the fit to the set of most accurate experimental data and tested on all other available data. The obtained 11Li ground state wave function allows to describe all considered experimental data within their error bars simultaneously. The main contributions to the 11Li ground state wave function are found to come from ( s 1 / 2 ) 2 (37%) and ( p 1 / 2 ) 2 (47%) components.

Systematic Study of 9,10,11Li with the Tensor and Pairing Correlations

We make a systematic study of Li isotopes (A=9,10,11) in the tensor optimized shell model for 9Li and treat the additional valence neutrons in the cluster model approach by taking into account the Pauli-blocking effect caused by the tensor and pairing correlations. We describe the tensor correlations in 9Li fully in the tensor-optimized shell model, where the variation of the size parameters of the single particle orbits is essential for getting strong tensor correlations. We have shown in our previous study that in $^{10,11}$Li the tensor and pairing correlations in 9Li are Pauli-blocked by additional valence neutrons, which make the p-shell configurations pushed up in energy. As a result, the $s^2$ valence neutron component increases to reveal the halo structure of 11Li and the inversion phenomenon of the single particle spectrum in 10Li arises. Following the previous study, we demonstrate the reliability of our framework by performing a detailed systematic analysis of the structures of $^{9,10,11}$Li, such as the charge radius, the spatial correlation of halo neutrons of 11Li and the electromagnetic properties of Li isotopes. The detailed effects of the Pauli-blocking on the spectroscopic properties of $^{10,11}$Li are also discussed. It is found that the blocking acts strongly for the 11Li ground state rather than for 10Li and for the dipole excited states of 11Li, which is mainly caused by the interplay between the tensor correlation in 9Li and the halo neutrons. The results obtained in these analyses clearly show that the inert core assumption of 9Li is not realistic to explain the anomalous structures observed in $^{10,11}$Li. For the dipole excitation spectrum of 11Li, the effect of the final state interactions is discussed in terms of the dipole strength function.

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.

Analytical E1 strength functions of two-neutron halo nuclei: 11Li and 14Be

An analytical model, recently developed to study the electromagnetic dissociation (EMD) energy spectra of two-neutron halo nuclei, is applied to 11Li and 14Be. We find that a reliable set of experimental data on EMD could help to resolve the problem concerning the structure of the 11Li ground state. For 14Be we find a mutual inconsistency between the existing experimental data on the binding energy, radius and EMD energy spectrum. We also conclude that the structure of 14Be is essentially more complicated than the structure of other Borromean two-neutron halo nuclei.

Super-strong β-decay of 11Li into 11Be ∗ (18 MeV) state: a probe for halo p-wave component?

An experimental study of β-delayed charged particles (H, He, Be), neutrons and γ-rays that follow the 11Li β-decay, clearly indicates a β-feeding to an exited state at 18.1 MeV in 11Be with a large Gamow-Teller strength, B GT ≥ 1.0. The large strength of this β-transition implies a broad overlap of the 11Be ∗ state at 18.1 MeV and the ground state of 11Li. The deduced width of this resonance is ≅ 1 MeV. A strong suppression of the branch from 18.1 MeV state into the 10Be+n channel is observed. This branch, with the largest decay energy, has a partial width less than 1% of the total width. A centrifugal barrier consideration fails to explain this effect. A possible consequence of the observed effect for the 11Li structure is that the admixture of (p 1 2 ) 2 configuration in 11Li might be small.

Structure of Neutron-Halo in the Ground State of 11Li

(Received January 8, 1990) The structure of the neutron-halo in the ground state of Li is studied in the microscopic framework of the cluster-orbital shell model and the extended cluster model. Both of the models are understood to playa complementary role in gaining the correlation energies for the two types of relative motions between 9Li and the valence neutron and between the two neutrons. The lack of the binding energy of the cluster-orbital shell model is shown to be accounted for by the introduction of the hybrid model combining it with the extended cluster model. The hybrid model leads us to a plausible explanation of the binding mechanism of the 9Li + n + n three body system in which no pair of the constituent particles forms a bound state.

Ground-state configurations of10Li and11Li

Evidence is given that the ground state of 10Li has non-normal parity and that the ground state of 11Li has large admixtures of higher configurations, the situations, being similar to those in 11Be and 12Be respectively. It is concluded that ground-state masses of these nuclei should be used only with cation in mass relations.