Structure of 10Li and 11Li

Recent two-body nuclear reaction measurements of the struture of ¹⁰Li and ¹¹Li are reviewed. The mass of ¹¹Li is now well known, but the situtation for ¹⁰Li is not so clear. However recent evidence presented at this conference seems to confirm the existence of a slightly unbound s-wave ground state.     

Three-Body Structure of 11Li

A variational calculation for neutron rich nucleus l1 Li is made in the ⁹Li + n + n model. The ⁹Li-neutron and neutron-neutron interactions are chosen to be of the Gaussian potentials with a repulsive core and an attractive tail. The strlicture and interparticle correlations are studied. A direct verification supporting neutron halo structure is found by inspecting the correlated densities.     

Coulomb dissociation of 11Li

We use a semiclassical treatment of the coupled-channels problem to study the Coulomb dissociation of ¹¹Li projectiles on a heavy target. The comparison of our predictions with the data show good agreement for the energy spectrum and qualitative agreement for the velocity distribution. The effect of going beyond the dipole term of the electromagnetic coupling is studied and other improvements over the calculations presented in a previous work are also considered.     

Nuclear charge radius of 11Li

We have determined the nuclear charge radius of ¹¹Li by high-precision laser spectroscopy. The experiment was performed at the TRIUMF-ISAC facility where the ⁷Li-¹¹Li isotope shift (IS) was measured in the 2s→3s electronic transition using Doppler-free two-photon spectroscopy with a relative accuracy better than 10⁻⁵. The accuracy for the IS of the other lithium isotopes was also improved. IS’s are mainly caused by differences in nuclear mass, but changes in proton distribution also give small contributions. Comparing experimentally measured IS with advanced atomic calculation of purely mass-based shifts, including QED and relativistic effects, allows derivation of the nuclear charge radii. The radii are found to decrease monotonically from ⁶Li to ⁹Li, and then increase with ¹¹Li about 11% larger than ⁹Li. These results are a benchmark for the open question as to whether nuclear core excitation by halo neutrons is necessary to explain the large nuclear matter radius of ¹¹Li; thus, the results are compared with a number of nuclear structure models.     

The quadrupole moment of the neutron-halo nucleus11Li

The quadrupole moment ratio of⁹Li and¹¹Li was measured by a combination of in-beam laser induced nuclear polarization and Β-NMR in LiNbO₃. The result ¦Q(¹¹Li)/Q(⁹Li)¦=1.14(16) is consistent with cluster models describing¹¹Li as composed of a⁹Li core and a far extended halo of two loosely bound neutrons.     

Photodisintegration of 11Li and Radiation Capture of Two Neutrons by 9Li

Photodisintegration of ¹¹Li and radiation capture of two neutrons by ⁹Li are studied in the frame of algebraic version of resonating group method and in asymptotic potential approximation. The behavior of the scattering phases shows on the existence of J ^π=3/2⁺ and J ^π=5/2⁺ resonances in continuum above the three-body decay threshold ¹¹Li→⁹Li+n + n. The cross-section of photodisintegration as well as the cross-section of radiation capture have been received. Energetic dependence of the first one is in good correspondence with the experimental data.     

Fusion cross-section of the 7Li + 11B reaction

The ⁷Li + ¹¹B reaction has been investigated in the energy range 5.5 MeV < E _lab < 19MeV, by detecting γ-ray resulting from the de-excitation of evaporation residues. Statistical compound-nucleus calculations have been performed in order to extract both the cross-sections of individual exit channels and the fusion cross-section of the system. The total angular momentum that the compoundn ucleus ¹⁸O can support has been deduced and is seen to exhibit saturation for a limiting value of 8.5ħ at the high-energy extreme. The results are discussed in terms of the entrance channel and statistical yrast line limitations.     

New binding energy for the two-neutron halo of 11Li

The extended radius of a halo nuclide is very sensitive to the minute binding energy of its valence nucleons. The binding energy of 11Li has been measured with high precision by using the radio-frequency spectrometer MISTRAL at CERN's ISOLDE facility. The new two-neutron separation energy of 378+/-5 keV is 25% higher than the previously accepted value with an uncertainty 5 times smaller.     

Precision measurement of 11Li moments: influence of halo neutrons on the 9Li core

The electric quadrupole moment and the magnetic moment of the 11Li halo nucleus have been measured with more than an order of magnitude higher precision than before, |Q| = 33.3(5) mb and mu = +3.6712(3)muN, revealing a 8.8(1.5)% increase of the quadrupole moment relative to that of 9Li. This result is compared to various models that aim at describing the halo properties. In the shell model an increased quadrupole moment points to a significant occupation of the 1d orbits, whereas in a simple halo picture this can be explained by relating the quadrupole moments of the proton distribution to the charge radii. Advanced models so far fail to reproduce simultaneously the trends observed in the radii and quadrupole moments of the lithium isotopes.     

Energy dependence of11Li dissociation cross section

The Coulomb breakup cross section of¹¹Li is calculated as a function of its bombarding energy. Comparison is made to cross sections at 790 MeV/nucleon and 30 MeV/nucleon. Low energy reactions on a high-Z target show a greatly enhanced Coulomb breakup cross section that is more sensitive to the distribution of dipole response strength than high energy reactions thus providing more structure information.     

Transverse momentum distributions of a 9Li fragment in the (11Li, 9Li) reaction and neutron correlations

The transverse momentum distribution of a ⁹Li fragment from the (¹¹Li, ⁹Li) reaction at an incident energy of 800 MeV/nucleon is calculated within the Glauber theory and compared with the longitudinal one. The both distributions are not very much different at high energy. A simple hybrid model wave function[1] comprising both aspects of shell model and di-neutron cluster model gives a reasonable fit to the measured distribution.     

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.     

Towards the determination of the charge radius of 11Li 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. This revised version was published online in August 2006 with corrections to the Cover Date.