Radiative neutron capture by 2H, 7Li, 14C, and 14N nuclei at astrophysical energies

The possibility of describing experimental data on the total cross sections for the n ²H, n ⁷Li, n ¹⁴C, and n ¹⁴N radiative-capture processes within the potential cluster model involving forbidden states and their classification according to Young’s tableaux is considered. It is shown that this model and the methods used here to construct potentials make it possible to describe correctly the behavior of the experimental cross sections at energies between 5 to 10 meV (5 × 10^?3–10 × 10^?3 eV) and 1 to 15MeV.     

β-delayed neutron decay of drip line nuclei 11Li and 14Be

Experimental studies of β-decay measurements of the neutron drip line nuclei ¹¹Li and ¹⁴Be are presented. β- decay schemes of these nuclei are determined by measuring β-rays, delayed neutrons and γ-rays in triple coincidence. The decay schemes of both ¹¹Li and ¹⁴Be associated with single neutron emission are unambiguously determined. New levels in their daughter nuclei, ¹¹Be and ¹⁴B, are found. In addition, the deduced level scheme of 14B indicates the lowering of 2s _1/2 single neutron orbital with respect to 1p _1/2 orbital in the N=9 isotones. Such behavior is known to exist in N=7.     

Experimental investigation of highly excited states of the 5,6He and 5,6Li nuclei in the (6Li, 7Be) and (6Li, 7Li) one-nucleon pickup reactions

The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions on ⁶Li and ⁷Li nuclei were investigated in the angular interval 0°–20° in the laboratory system at a ⁶Li energy of 93 MeV. In addition to low-lying states of the ^5,6He and ^5,6Li nuclei, broad structures were observed near the t(³He)+d and t(³He)+t thresholds at the excitation energies of 16.75 (3/2⁺) and ～20 MeV (for ⁵He), 16.66 (3/2⁺) and ～20 MeV (⁵Li), 14.0 and 25 MeV (⁶He), and ～20 MeV (⁶Li). The angular distributions measured in the ⁷Li(⁶Li, ⁷Be)⁶He reaction for transitions to the ground state (0⁺) and excited states at E _x=1.8 MeV (2⁺) and 14.0 MeV of the ⁶He nucleus were analyzed by the finite-range distorted-wave method assuming the 1p-and 1s-proton pickup mechanism. The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions were shown to proceed predominantly through the one-step pickup mechanism, and the broad structures observed at high excitation energies are considered as quasimolecular states of the t(³He)+d and t(³He)+t types.     

Isotopic effects in the 7Li + 10, 11B elastic and inelastic scattering

Angular distributions of the ⁷Li + ¹⁰B elastic and inelastic scattering were measured at the energy E _lab (¹⁰B) = 51 MeV (21 MeV c.m.). These and previously measured ⁷Li + ¹⁰B elastic-scattering data known at the ⁷Li-beam energies 24 MeV (14.1 MeV c.m.) and 39 MeV (22.94 MeV c.m.) were analyzed within the optical model and coupled-reaction channels method to determine the energy dependence of the parameters of the scattering potential and find the difference of these parameters from that of ⁷Li + ¹¹B scattering. It was found that the ⁷Li + ¹¹B potential parameters fail to describe the ⁷Li + ¹⁰B scattering data. The biggest difference is observed between the depths of the imaginary potentials that describe these scatterings.     

Levels of188Os populated by thermal neutron capture

Direct and coincidence gamma spectroscopy has been applied to the reaction¹⁸⁷Os(n, γ)¹⁸⁸Os. A neutron binding energy of 7,989.3±0.3 keV is deduced and a level scheme is established. The experimental level energies andB(E2) ratios are compared to calculations in the framework of the Interacting Boson Model.     

Observation of abnormally large radii of nuclei in excited states in the vicinity of neutron thresholds

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/2₁⁺ state of the ¹³C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the ⁹Be (1/2⁺ level at 1.68 MeV and 5/2⁺ level at 3.05 MeV) and ¹¹Be (5/2⁺ level at 1.78 MeV and 3/2⁺ level at 3.41 MeV) nuclei, and for the 2₁⁺ state of the ¹⁴Be nucleus at 1.54 MeV and 1₁⁻ state of the ¹²Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos.     

Properties of nuclear levels excited by neutron capture γ-rays from cobalt

Neutron capture γ-rays from cobalt have been used to photoexcite nuclear levels in the 5–8 MeV region. The decay properties of the 7491 keV level in ⁵⁵Mn and the 6877 keV level in ¹⁴²Nd were studied in detail. Total and partial radiative widths of nuclear levels in several isotopes were determined using nuclear self-absorption, temperature variation, and absolute scattering cross section measurements. The total radiative widths were found to be of the same magnitude as those of unbound levels populated in neutron resonances. The spins and parities of some resonance levels were determined by carrying out angular distribution and polarization measurements, respectively.     

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.     

Electron capture in collisions of Li~(3+) ions with ground and excited states of Li atoms

The electron capture processes in collisions of Li~(3+)ion with Li(1s~22s)and Li(1s~22p_(0,1))are investigated by using the two-center atomic orbital close-coupling method in the energy range from 0.1 keV/u to 300 keV/u.The interaction of the active electrons with the target ion is represented by a model potential.The present results for the Li~(3+)–Li(1s~22s)system are compared with the available theoretical data and general agreement is obtained for the high collision energies.It is also found that the total and partial electron capture cross sections are sensitive to the initial charge cloud alignment in the low energy region.     

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.     

Quasielastic triton knockout from 6Li and 7Li nuclei by intermediate-energy pions

Quasielastic triton knockout from ⁶Li and ⁷Li nuclei by negative pions with momenta p ₀=0.72 and 0.88 GeV/c was studied in the region of backward pion-triton scattering. The experiment was performed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) on a 3-m magnetic spectrometer equipped with spark chambers. The momentum distributions of the intranuclear quasitriton motion and the excitation-energy spectra of residual nuclei were obtained.     

Model-independent calculation of radiative neutron capture on lithium-7

The radiative neutron capture on lithium-7 is calculated model independently using a low-energy halo effective field theory. The cross section is expressed in terms of scattering parameters directly related to the S-matrix elements. It depends on the poorly known p-wave effective range parameter r(1). This constitutes the largest uncertainty in traditional model calculations. It is explicitly demonstrated by comparing with potential model calculations. A single parameter fit describes the low-energy data extremely well and yields r(1)≈-1.47 fm(-1).     

Spectroscopy of 41K by thermal neutron capture in 40K

The γ-ray spectrum emitted after thermal neutron capture in ⁴⁰K has been studied at the ILL high flux reactor with curved crystal Bragg, pair and Ge(Li) spectometers. 585 transitions were assigned to the reaction ⁴⁰K(n, γ)⁴¹K and 490 of them were placed into a ⁴¹K level scheme; 68 new states are proposed. On the basis of γ-ray branches to states with established spin and parity, many new spin-parity assignments were made. The level energies up to 4 MeV were measured with a precision of 8–50 eV relative to the 411.8 keV ¹⁹⁸Au standard, those above 4 MeV with a precision of 50–100 eV. The spin of the capture state was found to be $\text{I =}\text{7}\text{2}$; the neutron binding energy was determined to E_B = 10095.25(10) keV. The level density of $\text{I}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{\pm }}\text{,}\text{7}\text{2}{}^{\mathrm{\pm }}\text{,}\text{9}\text{2}{}^{\mathrm{\pm }}$ states was analyzed in terms of the constant-temperature Fermi gas model. It was shown that in this spin window the level scheme is almost complete up to an excitation energy of 5 MeV.     

Study of excited states of atoms by means of nonorthogonal radial orbitals

Rules are derived for graphical determination of the overlap integral of wave functions and matrix elements of operators of physical quantities. A calculation is made for four-electron atoms in the configuation 1s²2s4s using nonorthogonal radial orbitals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 7–11, March, 1981.     

Optically in accessible core excited states of Li and Na

The first observations of a number of optically inaccessible core-excited autoionizing states of lithium and sodium have been made. For example, the (1s2s²)²S and (1s2p²)²D states of Li have excitation energies of 56.31±0.03 and 61.04±0.03 eV, respectively.     

A study of excited states of5He by the7Li (d, α)5He-reaction

The interactions of deuterons with⁷Li, in which two α-particles and a neutron are produced in the final state are studied atE _d =1.2 MeV. The dual parameter α-α coincidence spectrum was analyzed with a search program. The results indicate two excited states of⁵He: One at excitation energy 2.9±0.1 MeV and with a reduced width of γ²=1.1±0.4 MeV, and the other at 4.8±0.4 MeV, with γ²=0.9±0.4 MeV. No contributions of sequential decay through the 4⁺ state in⁸Be or direct three body decay was observed.     

Investigation of highly excited states of calcium by three-photon ionization

The three-photon ionization in Ca from S₀ ground state is studied. The two-photon process is a near -- resonance process with one of the following bound states: 4s4d ¹D₂, 4p P₂, 4s6s ¹S₀, 4 D₂ and 4 S₀ while the third photon reach either directly the continuum or one of the autoionizing states. The succession of bound states as well as the transitions above the ionization limit are discussed. The dynamics of the multiphoton excitation processes is also discussed and radiative decay of 4 S₀ Ca state with two-photon excitation as well as (the measured) decay times of the Ca autoionizing states using the proper line profiles for different quantum numbers has been determined.Received: 29 September 2003, Published online: 18 May 2004PACS: 32.70.-n Intensities and shapes of atomic spectral lines - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Fb Photoionization of atoms and ions - 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Structural Nature of 7Li and 11B Sites by Static NMR and MAS NMR in Nonlinear Optical Material LiCsB6O10

The relationship between structure and nonlinear optical properties in LiCsB₆O₁₀ is characterized using single-crystal nuclear magnetic resonance (NMR) and magic-angle spinning (MAS) NMR. Although the quadrupole parameters for B(1) and B(2) sites were obtained using single-crystal NMR, the T ₁ values for these atomic sites could not be distinguished in this way. Thus, the structural nature of lithium and boron sites in LiCsB₆O₁₀ was investigated using MAS NMR. B(1) and B(2) sites could be distinguished based on the spectrum and T _1ρ obtained from ¹¹B MAS NMR. In addition, the T ₁ and T _1ρ values and activation energies for ⁷Li and ¹¹B are compared. No significant changes were seen in the T _1ρ at the lithium and boron nuclei in LiCsB₆O₁₀.     

Transition probabilities and static moments of excited states in even-even nuclei

A new approach is made to calculate the generalized single-particle density matrixp ^μv in even-even nuclei. It is shown that this quantity is included in the three particle response function, for which we derived a renormalized equation. Taking into account in a consequent way the effective particle-hole interaction we received a formula for the static moment of excited states and the transition probability between such states which is essentially different from the usual RPA theory.