Excited State Of 7Li Research Articles

Fast neutron inelastic scattering from 7Li

The inelastic scattering of fast neutrons from 7Li nuclei was investigated at the nELBE neutron-time-of-flight facility. The photon production cross section of 478 keV γ-rays from the first excited state of 7Li was determined by irradiating a disc of LiF with neutrons of energies ranging from 100 keV to about 10 MeV. The target position was surounded by a setup of 7 LaBr3 scintillation detectors and 7 high-purity germanium detectors to detect the de-excitation γ-rays. A 235U fission chamber was used to determine the incoming neutron flux. The number of detected photons was corrected for the detection efficiency, multiple scattering and the time-of-flight dependent data acquisition dead time. The preliminary results show reasonable agreement with some previous measurments but are about 15 % below the recent data taken at the GELINA facility.

Elastic and inelastic scattering of 14N ions by 7Li at 80 MeV (c.m. 26.7 MeV)

New angular distribution data for 7Li + 14N elastic and inelastic scattering at the energy $ E_{lab}$ $({}^{14}N) = 80$ MeV (c.m. 26.7MeV) are presented. The data were analyzed within the optical model and the coupled-reaction-channels method using a channels-coupling scheme that included the 7Li and 14N inelastic scattering channels, spin reorientations of 7Li and 14N as well as most important transfer reactions. The low-energy excited states of 7Li and 14N were assumed to be collective in nature. The 7Li + 14N potential parameters as well as deformation parameters of 7Li and 14N were deduced. The 7Li + 14N potential and the data were compared with those of 6Li + 14N to observe isotopic differences. The enhanced large-angle elastic and inelastic scattering data are shown to have a large contribution from the ground-state reorientation of 7Li.

Astrophysical Rates for the 6He(p, γ)7Li Reaction

Angular distribution of the 6He(d,n)7Li reaction at Ec.m.=9.1 MeV is measured in inverse kinematics for the first time. The proton spectroscopic factors for the ground and first excited states of 7Li are derived by using the distorted wave Born approximation analysis. The astrophysical rates of 6He(p, γ)7Li reaction are then deduced and fitted with an expression of REACLIB.

Single-Proton Pickup Reaction of the HaloNucleus 6He on a 9Be Target at 25 MeV/nucleon

The inclusive differential cross sections of the 7Li nucleusin a reaction induced by 6He on a 9Be target are measured atan incident energy of 25 MeV/nucleon. Finite-range distorted-wave Bornapproximation calculations suggest that these 7Li particles areformed in a direct single-proton pickup reaction9Be(6He,7Li)8Li. The experimental data can be wellreproduced by taking into account of the contributions of both theground states and the first excited states of 7Li and 8Li.

Investigation of7Be(n,p)7Li reaction

The7Be(n, p)7Li nuclear reaction with thermal and 2 keV neutrons was studied. For thermal neutrons the total cross section of (46 800± 4 000) b was obtained and the proton branching ratio to the first excited and ground states of7Li was determined to beσ 1/σ0 = (2±1) %. For 2 keV neutrons the upper limit of the cross section of 540 b was estimated.

The value of B(E2; [formula omitted]− → [formula omitted]−) FOR 7Li

Previous experimental information from the Coulomb excitation of the 1 2 − first excited state of 7Li is discussed and reanalysed, giving B(E2; 3 2 − → 1 2 −) = 7.59 ± 0.10 e 2 · fm 4 .

Study of the one-neutron transfer reactions induced by polarized 7Li ON 26Mg and 120Sn

Abstract Angular distributions of the cross sections and analyzing powers up to third rank have been measured for the one-neutron transfer reactions 26Mg(7Li,6Li)27Mg, 120Sn(7Li,6Li)121Sn and 120Sn(7Li, 8Li)129Sn initiated by polarized 7Li ions of 44 MeV. Third-rank analyzing power has been measured for the first time in transfer reactions. Coupled-channels calculations in which the ground and first excited states of 7Li are coupled together by collective interactions and one-neutron transfers are calculated in exact finite range explain the experimental data for low-lying states in final nuclei. Extracted spectroscopic factors are in good agreement with those obtained from other one-neutron transfer reactions on the same targets.

Prompt gamma as a fluence rate monitor in neutron beam experiments

An accurate measurement of the neutron lifetime requires a determination of neutron fluence rate to an accuracy of a few tenths of a percent. The10B(n,α)7 Li reaction offers the possibility of achieving this uncertainty. The thermal cross section is large and its departure from 1/v behavior is about 3 parts in 10000. The principal alpha branch is to the first excited state of7Li which then decays by emission of a 478 keV gamma ray. The measurement of the gamma branch can be made with boron samples that totally absorb thermal neutrons, allowing greater sensitivity and eliminating the uncertainty of target thickness. The absolute efficiency of the gamma detector can be determined by an alpha-gamma coincidence technique. Preliminary investigations of this method are presented with a discussion of the problems that must be overcome to achieve the desired uncertainty.

Elastic and inelastic scattering of polarised7Li from120Sn

The differential cross section and analysing powers iT11, TT20, T20, T21 and TT30 have been measured for both the elastic scattering of 44 MeV polarised 7Li from 120Sn and for projectile excitation to the 1/2 state at 478 keV. The data have bee fitted with coupled-channels calculations which include ground-state reorientation of the 7Li and coupling to excited states of 7Li. The sensitivity of the different observables to a number of coupling schemes is discussed. The potentials were derived from a double folding model which explicitly includes the 7Li deformation.

Five-nucleon transfer in the12C(d,7Li)7be reaction atE lab=78.0 MeV

Angular distributions of the12C(d,7Li)7Be reaction to the ground and to the unresolved first excited states of7Li or7Be nuclei were measured in the entire angular region in the centre of mass system atElab=78.0 MeV. Both the one-step five-nucleon cluster transfer as well as two-step sequential transfers were considered in the theoretical analysis. The former mechanism was found to dominate, but the latter is also not negligible.

Inelastic scattering of pions on7Li

The recent experimental results of Gibson and coworkers, for inelastic scattering of pions on7Li, leading to the first five excited states of7Li are analyzed using a shell model description including configuration admixtures and representing the transition nucleon densities following Helm model, used extensively in the context of inelastic scattering of electrons. With the transition radii for protons and neutrons chosen to be 3.9 fm and 4.1 fm respectively, good fits to the experimental cross sections are obtained. In contrast to the distorted wave Born approximation (dwba) calculations using optical model codes, we find the present work is able to reproduce the observed maxima and minima precisely. Moreover this analysis reveals the importance of considering the configuration admixtures especially in the transitions to24 P 5/2 (7.48 MeV) and24 D 7/2 (9.67 MeV) levels.

Coulomb Excitation of 7Li

Coulomb excitation of the 0�478 MeV, J1t = t-, first excited state of 7Li has been studied using beams of 7Li ions and targets of 138Ba and 208Pb. Spectra of the scattered particles were measured at 171� using an annular Si surface-barrier detector (l 38Ba and 208Pb targets) and at 90� using an Enge split-pole magnetic spectrometer (208Pb targets). For each experimental configuration, the bombarding energy at which nuclear interference became significant was determined experimentally. An analysis based upon the reorientation effect yielded the following results: the static electric quadrupole moment of the J1t = t- ground state (Q3/2-) is -4�0� 1�1 efm", the contribution of the giant dipole resonance (GDR) to the Coulomb-excitation cross section is 2�7 �0�2 times as great as would be calculated from the hydrodynamic model, and B(E2;t-~t-) is 7�42�0�14e2fm4 ? The value obtained for Q3/2- is in excellent agreement with results reported from atomic- and molecular-beam spectroscopy and from Coulomb scattering of aligned 7Li. Thus it provides a strong verification of the validity of the reorientation-effect technique for the determination of nuclear quadrupole moments, provided that the GDR effect is treated adequately.

Polarized deformed spin [formula omitted] projectile scattering and complex folded potentials

A formalism is presented where polarization observables of all ranks for deformed spin − case3 2 projectiles are calculated in a parameter-free fashion. Complex optical potentials for the available 7 Li + 58Ni elastic scattering data at E lab = 20.3 MeV are obtained from single folding calculations, taking the 7Li ground state to be an α + t cluster in relative p-state. The expansion of the hamiltonian in spin-space generates tensor terms of ranks 2 ( T R ) and 3 ( T 3) apart from the usual central and spin-orbit terms. The T R potential fits the second-rank tensor analysing powers quite well without being able to resolve discrete ambiguities of input optical parameters. The T 3 term generates a J · L contribution, making the spin-orbit interaction three-component. The 7Li vector analysing power so obtained is negative, but the magnitude is not fully reproduced. Modification of parameters to account for absorption modes not included in the superposition model indicates the need for properly handling dynamical polarization effects due in particular to the low-lying first excited state of 7Li.

States in 8Li from an R-matrix analysis of 7Li(n, n) 7Li and 7Li(n, n′) 7Li ∗ (0.478, 4.63) measurements

A comprehensive multilevel multichannel R-matrix analysis of 7Li+n scattering data has been completed. All available neutron elastic scattering and inelastic scattering data to the first two excited states of 7Li up to 8 MeV incident neutron energy were included in the analysis. Good over-all fits to all cross-section data throughout this energy range were obtained. In this study six previously unknown levels in 8Li have been identified and spin and parity assignments for these and all previously identified levels in 7Li except the very narrow one at E x = 6.53 MeV have been made. The present results are in excellent agreement with previous analyses and model calculations.

Transfer of state multipoles in excited A 1Σ +u7Li 2 following rotationally inelastic collisions with He: Experiment and theory

Circularly polarized dye laser radiation is used to prepare rotational levels j = 1 to j = 20 of the A 1Σ + u excited state of 7Li 2 with well defined values of the state multipoles K = 0, 1 and 2. Inelastic collisions with helium atoms populate other j levels and we have measured the circular polarisation ratio of emission, C, from these levels. C is plotted versus final j′ for each value of Δ j from +2 to +18 and a family of curves is obtained which may be used as a critical test of current theories. The results are interpreted in terms of cross sections σ K for transfer of the state multipoles under isotropic collision conditions. The observation of substantial polarisation following inelastic collision indicates that the σ K are dominated by certain restricted scattering channels. Relative magnitudes of the multipole cross sections are calculated using the “ l-dominant”, “restricted Δ m j channels” nd the Born approximation. These cross sections are then used to calculate C.

The influence of hyperfine coherence and of elastic collisions on the circular polarisation of emission from Li 2

This paper gives an account of the factors that influence the degree of involvement of nuclear hyperfine interactions in determining the polarisation ratios of low J′ levels of diatomic molecules excited by circularly polarised light. Experimental estimates are obtained for the nuclear hyperfine coupling constant of the 1Σ u + excited state of 7Li 2. The role of foreign gas collisions is also considered and cross sections for the destruction of orientation obtained for J′ = 10.

Cross Section for the 9Be(n, t1)7Li Reaction Between 13.3 and 15 MeV

The magnitude and energy dependence of the 9Be(n,t1)7Li reaction have been measured between 13.3.- and 15-MeV neutron energy by observing the gamma decay of the first excited state of 7Li with a Ge...

(n, t) and (n, α) reactions on 9Be

A metallic 9Be target was bombarded with 13.99 MeV neutrons; α-particles, tritons and 6He recoil nuclei were detected and identified with a telescope consisting of two proportional counters and a solid state detector. Absolute differential cross sections were measured for the (n, t) reactions leading to the ground state and first excited state of 7Li and for the (n, α) reactions leading to the ground state and first excited state of 6He. No evidence for higher excited states in 6He has been found. An attempt has been made to interpret the observed (n, α) angular distributions in terms of the direct reaction model.

Transverse form factors of 7Li calculated with projected Hartree-Fock wave functions

Transverse magnetic and electric contributions to the high-energy electron scattering at 180° from the ground state and first excited state of 7Li are calculated using projected Hartree-Fock wave functions obtained previously The results are compared with experiment and with the LS coupling shell model

Coulombformfaktoren für7Li

Using refined clustermodel wave functions the Coulomb form factors for the elastic scattering of electrons as well as the formfactors for the inelastic scattering leading to the first and second excited states of7Li have been calculated.