Effect of cluster polarization on the spectrum of the <Superscript>7</Superscript>Li nucleus and on the reaction <Superscript>6</Superscript>Li(<Emphasis Type="Italic">n</Emphasis>, <Superscript>3</Superscript>H)<Superscript>4</Superscript>He

The effect of polarization of the ⁶Li and ³H clusters on the parameters of states of the ⁷Li nucleus and on the cross section for the reaction ⁶Li(n,³H)⁴He was studied. The ⁴He + d + n three-cluster configuration was invoked for this purpose, and cluster dynamics was determined within a microscopic model where the relative motion of the clusters was described in terms of Faddeev amplitudes. The ⁴He + d + n three-cluster configuration made it possible to consider the ⁴He + ³H and ⁶Li + n binary channels, which are dominant in ⁷Li, and to take simultaneously into account the cluster polarization of ⁶Li as a two-cluster subsystemin the ⁴He + d representation and the cluster polarization of ³Has a two-cluster subsystem in the d + n representation.     

High-lying excited states in <Superscript>10</Superscript>Be from the <Superscript>9</Superscript>Be(<Superscript>9</Superscript>Be,<Superscript>10</Superscript>Be)<Superscript>8</Superscript>Be reaction

A transfer-reaction experiment of ⁹Be(⁹Be, ¹⁰Be)⁸Be was performed at a beam energy of 45 MeV. Excited states in ¹⁰Be up to 18.80 MeV are produced using missing mass and invariant mass methods. Most of the observed high-lying resonant states, reconstructed from the α + ⁶He and t + ⁷Li decay channels, agree with the previously reported results. In addition, two new resonances at 15.6 and 18.8 MeV are identified from the present measurement. The 18.55 MeV state is found to decay into both the t + ⁷Li_g.s. and t + ⁷Li* (0.478 MeV) channels, with a relative branching ratio of 0.93 ± 0.33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

Fragmentation of <Superscript>7</Superscript>Li relativistic nuclei on a proton into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

In a track nuclear photoemulsion exposed to a beam of ⁷Li nuclei accelerated to a momentum of 3 GeV/c per nucleon at the synchrophasotron of the Joint Institute for Nuclear Research (JINR, Dubna), 13 events in which ⁷Li nuclei interacting with protons break up into ³H and ⁴He fragments were detected among 3730 inelastic-interaction events. For this fragmentation channel, the cross section was found to be 8 ± 2 mb. The average value of the fragment total transverse momentum was 214 ± 5 MeV/c. This value exceeds markedly the average value of the transverse-momentum transfer in the coherent dissociation of ⁷Li nuclei on track-emulsion nuclei (166±5MeV/c). The recoil-proton transverse momentum was on average 98% of the total proton momentum. The longitudinal-momentum distribution of protons was characterized by a variance of 16 MeV/c and a mean value of 37 ± 2MeV/c.     

Effect of the structure of neutron-rich <Superscript>8</Superscript>Li and <Superscript>9</Superscript>Li isotopes on the characteristics of proton elastic scattering

The differential cross sections of proton elastic scattering from ⁸Li and ⁹Li nuclei in inverse kinematics have been calculated. The cross sections were determined within the Glauber diffraction theory with the wave functions of nuclei in the three-particle α-t-n, α-t-2n, and ⁷Li-n-n models. Comparison with the existing experimental data for E = 700 and 60 MeV/nucleon made it possible to draw a conclusion about the quality of the wave functions and the adequacy of the potentials used for their calculations.     

On the hyperfine structures of the ground state(s) in the <Superscript>6</Superscript>Li and <Superscript>7</Superscript>Li atoms

The hyperfine structure of the ground 2²S-states of the three-electron atoms and ions is investigated. By using our recent numerical values for the doublet electron density at the atomic nucleus, we determine the hyperfine structure of the ground (doublet) 2²S-state(s) in the ⁶Li and ⁷Li atoms. Our predicted values (228.2058 and 803.5581 MHz, respectively) agree well with the experimental values 228.20528(8) MHz (⁶Li) and 803.50404(48) MHz (⁷Li [R.G. Schlecht and D.W. McColm, Phys. Rev. 142, 11 (1966)]). The hyperfine structures of a number of lithium isotopes with short lifetimes, including ⁸Li, ⁹Li, and ¹¹Li atoms are also predicted. The same method is used to obtain the hyperfine structures of the three-electron ⁷Be⁺ and ⁹Be⁺ ions in their ground 2²S-states. Finally, we conclude that our approach can be generalized to describe the hyperfine structure in the triplet n³S-states of the four-electron atoms and ions.     

Further study and analysis of the <Superscript>7</Superscript>Li on <Superscript>56</Superscript>Fe reaction at 50 MeV incident energy

We present deuteron and triton spectra measured at 12 laboratory angles from the reaction of 50 MeV ⁷Li on ⁵⁶Fe together with evaporative components as modeled by CASCADE and fitted to the backward angle data. The deuteron and triton “break-up” spectra obtained by subtracting the evaporative components from the measured spectra are also presented. The break-up of the ⁷Li projectile near the surface occurs with high probability and the major fraction of the break-up cross-section is taken by (⁷Li,α) transfer process. A crude estimate of the fraction of the total cross-section is found to be of the same order of magnitude as the overall spectroscopic factor determined by the diffraction model. The value of the estimated fraction of total cross section at 50 MeV incident energy is compared to that at 68 MeV incident energy for the same reaction. However, these values of estimated fraction of total cross section are found very much consistent with the measured yields at both incident energies. The importance of the level density parameter in locating the maximum of excitation energy is indicated in the diffraction model.     

Measurement of the excitation function for the <Superscript>7</Superscript>Li(t,p)<Superscript>9</Superscript>Li reaction using detection of delayed neutrons

The excitation function for the ⁷Li(t, p)⁹Li reaction is measured at the EGP-10 electrostatic tandem accelerator (VNIIEF) at the incident triton energies E _t = 5–11.3 MeV. The measurements were based on detection of delayed neutrons resulting from the decay of ⁹Li nuclei. The neutrons were detected by the 4π detector consisting of ³He counters enclosed in a polyethylene moderator. A pulsed mode was used for irradiating the LiF target (210 μg cm^?2) of natural isotopic composition on the tantalum backing. Absolutization of the excitation function was performed against the ⁷Li(p, n) reaction cross sections.     

Structure of neutron-rich Isotopes <Superscript>8</Superscript>Li and <Superscript>9</Superscript>Li and allowance for it in elastic scattering

The differential cross sections for elastic proton scattering on the unstable neutron-rich nuclei ⁸Li and ⁹Li at E = 700 and 60 MeV per nucleon were considered. The ⁸Li nucleus was treated on the basis of the three-body α-t-n model, while the ⁹Li nucleus was considered within the α-t-n and ⁷Li-n-n models. The cross sections in question were calculated within Glauber diffraction theory. A comparison of the results with available experimental data made it possible to draw conclusions on the quality of the wave functions and potential used in the calculations.     

Structure of the spatial periphery of the <Superscript>11</Superscript>Li and <Superscript>11</Superscript>Be isobars

On the basis of the shell model with an extended basis, the structure of ⁹Li-⁹Be to ¹¹Li-¹¹Be nuclei is examined with allowance for the competition of ^jj coupling and Majorana exchange forces via considering the sequential addition of neutrons, and the respective wave functions are determined. A formalism for calculating the spectroscopic factor for a dineutron and for individual neutrons in nuclei whose wave functions incorporate the mixing of shell configurations is developed. The reactions ⁹Li(t, p)¹¹Li and ⁹Be(t, p)¹¹Be treated with allowance for the mechanisms of dineutron stripping and a sequential transfer of two neutrons are considered as an indicator of the proposed structure of lithium and berylliumisotopes. The parameters of the optical potentials, the wave functions for the bound states of transferred particles, and the interaction potentials corresponding to them are determined from a comparison of the theoretical angular distribution of protons from the reaction ⁹Be(t, p)¹¹Be with its experimental counterpart. It is shown that a dineutron periphery of size about 6.4 fm is present in the ¹¹Li nucleus and that a single-neutron periphery of size about 8 fm is present in the ¹¹Be nucleus.     

<Superscript>23</Superscript>Na NMR in binary lithium-sodium cobaltite

Li_0.48Na_0.35CoO₂ lithium-sodium cobaltite was studied by means of wide-line ²³Na and ⁷Li NMR. A series of quantum-chemical calculations allowed to us determine the optimum positions of Li and Na atoms, to construct a map of the densities of electronic states near the Fermi level, and to estimate the electric field gradient on the Na nuclei. The results from these calculations are compared with experimental data from NMR and X-ray photoelectron spectroscopy     

Coupled-channels analysis of K<Superscript>+</Superscript> scattering from <Superscript>6</Superscript>Li and <Superscript>12</Superscript>C using the Watanabe superposition model

Coupled-channels calculations for the elastic and inelastic scattering of K⁺ at 715 MeV/c by ⁶Li and ¹²C at 635, 715 and 800 kaon Lab momenta have been analysed. The optical potentials of ¹²C and ⁶Li are calculated in terms of the alpha-particle and deuteron optical potentials. Good fits to the experimental data and phenomenological calculations are obtained for ⁶Li and ¹²C nuclei.     

Search for solar axions emitted in an <Emphasis Type="Italic">M</Emphasis>1 transition in <Superscript>7</Superscript>Li* nuclei

The resonance absorption of solar axions by ⁷Li nuclei, which is accompanied by the excitation of the first nuclear level of lithium a + ⁷Li → ⁷Li* → ⁷Li + γ, is sought. To this end, the energy spectrum has been measured by an HPGe detector that is surrounded by a LiOH layer. A new upper limit m_a ≤ 16 keV (at 90% C.L.) has been determined for the mass of the hadron axion.     

Puzzle of the <Superscript>6</Superscript>Li quadrupole moment: Steps toward solving it

The problem of the origin of the quadrupole deformation in the ⁶Li ground state is investigated with allowance for the three-deuteron component of the ⁶Li wave function. Two long-standing puzzles related to the tensor interaction in the ⁶Li nucleus are known: that of an anomalous smallness of the ⁶Li quadrupole moment (being negative, it is smaller in magnitude than the ⁷Li quadrupole moment by a factor of 5) and that of an anomalous behavior of the tensor analyzing power T_2q in the scattering of polarized ⁶Li nuclei on various targets. It is shown that a large (in magnitude) negative exchange contribution to the ⁶Li quadrupole moment from the three-deuteron configuration cancels almost completely the “direct” positive contribution due to the αd folding potential. As a result, the total quadrupole moment proves to be close to zero and highly sensitive to fine details of the tensor nucleon-nucleon interaction in the ⁴He nucleus and of its wave function.     

Production of mirror nuclei <Superscript>7</Superscript>Li and <Superscript>7</Superscript>Be in <Superscript>16</Superscript>O<Emphasis Type="Italic">p</Emphasis> interactions at a momentum of 3.25 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

Results of a comparative analysis of processes leading to the production of mirror nuclei ⁷Li and ⁷Be in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. A comparison of associated multiplicities of accompanying particles is performed. The first results on the mean multiplicity of neutrons appearing as fragments are described.     

Astrophysical <Emphasis Type="Italic">S</Emphasis> factors for radiative proton capture by <Superscript>3</Superscript>H and <Superscript>7</Superscript>Li nuclei

Within the potential cluster model where orbital states are classified according to Young diagrams and isospin, astrophysical S factors are considered for radiative proton capture by ³H and ⁷Li nuclei at energies of up to 1 and 10 keV, respectively. It is shown that the approach used, which takes into account only the E1 transition for the p ³H capture process, makes it possible to describe well the most recent experimental data at c.m. energies in the range from 50 keV to 5MeV. In the case of proton capture by ⁷Li nuclei, an M1 processwas taken into account in addition to the E1 transition, and a general behavior and the magnitude of the experimental S factor could be correctly reproduced owing to this at astrophysical energies, including the region around the resonance at 0.441 MeV (in the laboratory frame).     

Electronic states of CsLi and CsLi<Superscript>+</Superscript> molecules

Configuration interaction calculations have been carried out on electronic states of the CsLi molecule and the CsLi⁺ cation. Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels are presented for the lowest states of ^1,3Σ⁺, ^1,3Π, and ^1,3Δ symmetries of the alkali dimer CsLi molecule dissociating into Cs (6s, 6p, 5d, 7s, and 7p) + Li (2s, 2p, 3s, 3p, and 3d) as well as for the lowest ²Σ⁺, ²Π, and ²Δ electronic states of the CsLi⁺ cation dissociating into Li (2s, 2p, 3s, 3p, and 3d) + Cs⁺ and Li⁺ + Cs (6s, 6p, 5d, 7s, and 7p). The results of the present many-electron configuration interaction calculations on the cation support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s²) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some of the lowest states of the CsLi and CsLi⁺ molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries is related to a charge transfer process between the two ionic CsLi⁺ and LiCs⁺ systems.     

Peculiarities in total cross sections of reactions with weakly bound nuclei <Superscript>6</Superscript>He, <Superscript>9</Superscript>Li

The energy dependence of the total cross sections for the ⁶He + Si and ⁹Li + Si reactions was measured at beam energies between 5 and 20 MeV per nucleon. The results agree with experimental data published for the ⁶He + Si reaction. New data are obtained for the ⁹Li + Si reaction in the vicinity of a local enhancement of the total cross section. A theoretical analysis of the possible reasons behind the appearance of this peculiarity in the case of collisions of ⁶He and ⁹Li nuclei with silicon target nuclei is performed. In particular, the enhancement may owe its origin to the effect of loosely bound projectile nucleons.     

Heavy lithium isotope <Superscript>11,12</Superscript>Li production in pion absorption reactions on a <Superscript>14</Superscript>C radioactive target

The results from an experimental search for the production of heavy lithium isotopes ^11,12Li in stopped π⁻-meson absorption reactions on a ¹⁴C radioactive target are presented. A pronounced peak is observed in the missing mass spectrum of the ¹⁴C(π⁻, pp)X reaction, which is associated with the formation of a nucleon-unstable ¹²Li state with the following resonance parameters: E _R = 4.0 ± 0.2 MeV and Γ = 1.1 ± 0.2 MeV. Resonance parameters of three low-lying ¹¹Li excited states were determined in the ¹⁴C(π⁻, pd)X, reaction.     

Momentum distributions of <Superscript>4</Superscript>He nuclei from the <Superscript>6</Superscript>He and <Superscript>6</Superscript>Li breakup

Experimental data on the momentum distributions of ⁴He nuclei originating from ⁶He and ⁶Li breakup on various targets are presented over a wide beam energy range. The experiment with ⁶He was performed at the DRIBs accelerator complex for radioactive beams at the Joint Institute for Nuclear Research (JINR, Dubna). The intensity of the ⁶He beam used was 5 × 10⁶ particles per second and its energy was 10 MeV per nucleon. The momentum distributions of breakup products were measured by means of the MSP-144 magnetic spectrometer. The distribution width was shown to be virtually independent of the target mass. A small value of this width, σ ～ 28 MeV/c, confirms the presence of a halo in ⁶He. The measurements performed with ⁶Li beams of energy 18 and 46 MeV per nucleon at the U-400M accelerator yielded a width value of σ ～ 50 MeV/c for the momentum distributions of ⁴He nuclei, which is intermediate between that for ⁶He and those for stable nuclei. A compilation of the widths of the momentum distributions of fragments originating from the breakup of various nuclei is presented versus the binding energy of one or two neutrons in these nuclei, the target mass and the projectile energy.     

Ab initio calculation of the <Superscript>6</Superscript>Li binding energy with the hybrid multideterminant scheme

We perform an ab initio calculation for the binding energy of ⁶Li using the CD-Bonn 2000 NN potential renormalized with the Lee-Suzuki method. The many-body approach to the problem is the hybrid multideterminant method. The results indicate a binding energy of about 31MeV, within a few hundreds keV uncertainty. The center-of-mass diagnostics are also discussed.