Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in ⁶He and ⁶Be were investigated by using the ⁶Li(⁷Li, ⁷Be)⁶He reaction at 455 MeV and ⁶Li(³He, t)⁶Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at E _x =18.0±1.0 MeV in ⁶He and into ³He + ³He from one at E _x =18.0±1.2 MeV in ⁶Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for ⁶He and ⁶Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around E _x =18 MeV in ⁶He and ⁶Be.     

Tensor polarizabilities of levels of the configurations 4f 13 6s6p and 4f 12 5d6s 2 in thulium I

The level-crossing technique with parallel electric and magnetic fields was used to measure the tensor polarizabilities of six levels of the configuration 4f ¹³ 6s6p + 4f ¹² 5d6s ² in the Tm I-spectrum. Using intermediate coupling wave functions given by Camus and the experimental values of the tensor polarizabilities, the radial integrals for electric dipole transitions from levels of the configuration 4f ¹³6s6p + 4f ¹²5d6s ² to levels of the configuration 4f ¹³ 5d6s + 4f ¹² 6s ²6p have been determined. The results areI(4f ¹³6s6p,4f ¹³5d6s)=1.98(45)ea ₀ andI(4f ¹²5d6s ²,4f ¹²6s ²6p) = 0.88(25)ea ₀. A comparison between the experimental and the calculated values of the tensor polarizabilities shows an excellent agreement, provided that these radial integrals and the radial integrals for the electric dipole transitions to the ground state configuration 4f ¹³6s ² as determined by Wallenstein from lifetime measurements are used in the calculation, instead of radial integrals computed by Camus with Hartree-Fock wave functions.     

Identification of New Low-Lying Electronic States of the FeF Radical

Dispersed fluorescence studies on the ⁶Π-X⁶Δ and ⁶Φ−X⁶Δ systems of the FeF radical have resulted in the observation of vibrational progressions for transitions to the X⁶Δ state as well as at least two previously unobserved electronic states about 5000 cm⁻¹ above the ground state. The states are assigned as the A⁶Π and B⁶Σ⁺ electronic states. The spin components of both electronic states were found to be heavily perturbed resulting in uneven splittings between them. A third, weak series was also observed but could not be assigned. The (0,0) band of the ⁶Π_7/2−B⁶Σ⁺_5/2 transition at 398 nm was observed in absorption by laser induced fluorescence and its rotational structure was assigned. The spectra obtained were weak because of a poor population of the B⁶Σ⁺ state by the reaction used to form FeF. The levels were found to be markedly perturbed at high J values. Attempts were made to fit the data on the ⁶Π_7/2-B⁶Σ_5/2⁺ system to an effective Hamiltonian, but the presence of perturbations meant that the system is not well described by such a model.     

Hyperfine-structure and isotope-shift measurements in the 6s 5d↔6p 5d transitions of Ba I in the far-red spectral region

Measurements of the hyperfine structures in the 6p5d ¹ D ₂,³ D ₁ and³ F _{2, 3, 4} states of¹³⁵Ba and¹³⁷Ba, and isotope-shifts in several far-red transitions between the 6s 5d and 6p 5d configurations, as well as the transition 6s ^{2 1} S ₀→6s6p ³ P ₁ at 7,911 Å have been performed using high-resolution laser spectroscopy on a collimated atomic beam of natural barium. An analysis of the magnetic-dipole interaction in the 6p 5d configuration using effective one- and two-body hyperfine operators is presented. In particular the contact interaction was studied with respect to the correlation between the two valence electrons. Effects of strong configuration interaction were found. From a King-plot analysis of the isotope shift term- andJ-dependence of the field shift have been evaluated for the transitions between the 6s 5d and 6p 5d configurations. Relativistic Hartree-Fock (RHF) calculations have been performed of electron densities at the nucleus for six different configurations in Ba I and Ba II. The RHF calculations reproduce the experimental King-plot slopes quite well, while the absolute values, of the changes in electron density at the nucleus for the studied transitions, are found to be 9% lower than the results derived from a muonic experiment.     

A high resolution study of the transitions 4f 76s 2→4f 76s6p in the Eu I-spectrum

Eight transitions in the Eu I-spectrum connecting the ground state with configuration 4f ⁷ 6s ² with states of the configuration 4f ⁷ 6s6p were studied with high resolution laseratomic-beam spectroscopy. CW dye lasers operating in the wavelength regions 435–470 nm and 560–630 nm were used for this study. New data for the hyperfine structure in¹⁵³Eu were obtained as well as new and more accurate values for the isotope shifts between¹⁵¹Eu and¹⁵³Eu. The existing data for the hyperfine structure in¹⁵¹Eu were reproduced with an exception for the levelz ⁶ P _7/2.     

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.     

Radiative transition of two indirect excitons to direct exciton in thallous halides

Weak emission lines are observed at the energies far lower than the energies of edge emissions in TlCl and TlBr. They are explained as due to the radiative decay of two indirect X⁺₆ × R^?₆ excitons, both at the same M-point, by leaving one direct X⁺₆ × X^?₆ excitons through zero-phonon process.     

Neutron-induced charged-particle reactions in 6Li and 9Be

Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.     

Angular correlations from 6Li break-up near the Coulomb barrier of 118Sn and 208Pb

Absolute coincidence cross sections for three-particle final states have been measured inplane in the ⁶Li + ¹¹⁸Sn and ⁶Li +²⁰⁸Pb reactions at incident energies of 22.2 and 23.0 MeV, respectively. Most strongly populated is the α + d branch, proceeding sequentially through the first excited state (E_x = 2.18 MeV, J^π = 3⁺) of ⁶Li. The angular distributions are fitted by DWBA calculations including Coulomb interaction in the excitation of the projectile. The main competing reaction channels above and at the Coulomb barrier (¹¹⁸Sn: E/E_c ≈ 1.3; ²⁰⁸Pb: E/E_c ≈ 0.9) are: neutron transfer (⁶Li, αp) and the non-sequential α + d break-up of ⁶Li. The latter spectra are consistent with a quasi-free break-up mechanism. No ³He or tritons have been found in the coincidence spectra, as well as no evidence for a three-particle dissociation of ⁶Li into α + p + n.     

Resonant structure observed in the 3He(τ, γ)6Be capture reaction

The ³He(τ,γ)⁶Be capture reaction has been studied for ³He bombarding energies from 12 to 27, MeV. Transitions to the first excited state in ⁶Be(T = 1, 2⁺) are readily seen. Transitions to the ground state in ⁶Be (T = 1, 0⁺) are very weak and their presence could not be ascertained. The 90° excitation function for these transitions shows a broad maximum centered at E_τ = 23 ±1 MeV. This is interpreted as a resonance in the compound nucleus ⁶Be at E_x = 23.0±0.5 MeV with a configuration other than ³He+³He. These results are compared with other experimental work as well as with theoretical predictions.     

Intervalley magnetophonon resonance peak of thermoelectric power in the phonon drag region of p-Te

A large peak is found at 3.2 Tesla (T) in the second derivative curve of longitudinal magneto-Seebeck coefficient (-?²α₆/?H² of p-type tellurium below 20 K under the magnetic field H6c. The peak height is rapidly increasing with decreasing temperature, in contrast to disappearance of the usual oscillation due to LO phonon which is observed between 20 and 100 K. A small peak is also appreciable in the second derivative of longitudinal magnetoresistance (-?²?₆/?H² at the same field of 3.2 T. The peaks both in -?²α₆/?H² and -?²?₆/?H² are interpreted as a resonance peak due to the intervalley scattering by longitudinal acoustic (LA) phonon between the two valleys split off by inversion asymmetry splitting (μ_BGH). This interpretation gives a value of G as 5.5 in good agreement with the value of G = 5 ± 1 determined by the Shubnikov-de Haas experiment. It is explained by t he phonon drag effect based on this interpretation that the peak of -?²α₆/?H² is much more prominent than that of -?²?₆/?H² and increases with decreasing temperature.     

Deuteron exchange mechanism for the6Li(n, α) reaction at low energies

It is proposed that the major part of the low energy (l/v)⁶Li(n, α)³H cross section may be explained as being due to a direct deuteron exchange mechanism. This proposal is in agreement with recent experimental data on the spin-dependent⁶Li(n, α) cross section; it may be used to extract information on the⁶Li-αd vertex constant. The importance of the assumption of ad-exchange process for the⁶Li(n, α) angular distribution is discussed in the framework ofS-matrix theory.     

Study of complete and incomplete fusion for loosely bound projectiles 6He and 6Li on 165Ho and 166Er targets

Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loosely bound ⁶He and ⁶Li projectiles bombarding ¹⁶⁶Er and ¹⁶⁵Ho targets at energy of about 10 MeV/nucleon. Experiments were carried out to test an approach exploiting the measured intensities of ?? rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF reactions ¹⁶⁵Ho (⁶Li, ⁵ n) ¹⁶⁶Yb and ¹⁶⁶Er(⁶He, ⁶ n) ¹⁶⁶Yb as well as ICF ¹⁶⁵Ho (⁶Li, ??3n) ¹⁶⁴Er and ¹⁶⁶Er(⁶He, ??4n) ¹⁶⁴Er reaction channels were revealed from the obtained ??-ray data. The method of exit channel identification via the triple coincidence (??1-??2-light charged particle) was employed for these reactions study.     

Deformed states of high spin in42Ca

The⁴²Ca levels at 4,715 and 6,633 keV excitation energy have been investigated using the³⁹ K(α,pγ reaction atE _α=14 and 15 MeV. From particle-γ-ray angular correlations the spin assignmentsJ(4,715)=6, 4 andJ(6,633)=8, 6, 4 have been obtained. Lifetime measurements using the Doppler-shift attenuation method yieldedτ (4,715)=120±46 fs andτ(6,633)=52±21 fs. Both levels have positive parity and decay by enhancedE2 transitions. They are interpreted as theJ ^π=6⁺ and 8⁺ members, respectively, of theK ^π=0⁺ rotational band which has theE _x =1,837, 2,423 and 3,250 keV states as further members. The enhancement of inbandE2 transitions is 50 _?16 ⁺³⁵ W.u. (6→4) and 63 W.u. (8→6) respectively. The intrinsic quadrupole moments which have been derived on the basis of the coexistence model, areQ ₀=1.13?0.16/+0.37b(8→6) andQ ₀=1.36±0.25b(6→4), respectively. TheJ ^π=10⁺ member of the rotational band has possibly been observed as a level at 8,856±5 keV excitation energy.     

Hyperfine structure and isotope shift of high-lying metastable states of rhenium

Fourteen transitions in ReI, starting from high-lying metastable states belonging to the configurations (5d+6s)⁷, have been studied by laser-induced fluorescence in a collimated atomic beam, and accurate values for the isotope shifts in these transitions as well as for the hyperfine structure constants of 13 metastable and 9 excited states have been obtained. In addition, high precision measurements of the hyperfine structure of the states 5d ⁵ 6s ^{2 4} D _7/2 and 5d ⁶ 6s ⁶ D _{1/2, 3/2, 5/2, 9/2} have been performed using the atomic beam magnetic resonance technique coupled with laser-induced state-selective detection of metastable atoms. The analysis of the hyperfine structure data yields experimental evidence for far configuration mixing effects on the off-diagonal spin-dipole matrix elements. The phenomenological interpretation of the isotope shifts shows the significance of off-diagonal field-shift effects.     

The 6Li(α, 2α)2H reaction at 700 MeV and the α-d momentum distribution

The results of an experimental study of the reaction ⁶Li(α, 2α)²H at 700 MeV are given. A comparison with the data from seven other reactions pertaining to the α⁺d cluster structure of ⁶Li is presented. The amplitude for the virtual transition ⁶Li→α+d obtained three of these experiments and the present one are comparable. The internal momentum distributions extracted with the plane-wave impulse approximation in four of the experiments are compatible with a pole form, the width parameter being given by the α-separation energy in ⁶Li. The remarkable consistency among these results is seen as evidence for the validity of the simple models used for both the reaction mechanism (PWIA) and to describe the α d-vertex (pole approximation) in ⁶Li.     

Quark-quark spin-isospin-interaction and6Li(p, δ+ +)6He reaction

The elementary reaction pp→nΔ ^{+ +}, through which the⁶Li(p, Δ ^{+ +})⁶He reaction proceeds, is considered as the flip of spins and isospins of two quarks, one in each of the two quark bags of the interacting nucleons. Using the experimental data on the⁶Li(p, Δ ^{+ +})⁶He reaction at 1.04 GeV and the distorted wave Born approximation (DWBA) for the reaction mechanism, the strength of the spin-isospin quark-quark interaction is determined. It is found to be 70 MeV fm³.     

Experimentally determined transition probabilities of the systems 6p2→6p6d, 6p7s, 6p8s of neutral lead

Branching ratio measurements have been performed for all of the observed transitions from eight levels in neutral lead (6p²→6p6d, 6p²→ 6p7s, 6p²→6p8s) excited in a hollow cathode discharge in the 200–730 nm spectral range. From the relative emission intensity data, a set of absolute transition probabilities is derived for 28 lines, including lines for which transition probabilities have not been previously published. The absolute scales are obtained by averaging the measured lifetimes of the ³P⁰_1,2, ¹P_1⁰(6p7s), ³F^0_2,3, ³D^0_1,2(6p6d) levels.     

Efficient photo-ionization for barium ion trapping using a dipole-allowed resonant two-photon transition

Two efficient and isotope-selective resonant two-photon ionization techniques for loading barium ions into radio-frequency (RF)-traps are demonstrated. The scheme of using the strong dipole-allowed transition 6s ²? ¹S₀→6s6p? ¹P₁ at λ=553 nm as a first step towards ionization is compared to the established technique of using a weak inter-combination line (6s ²? ¹S₀→5d6p? ³D₁,λ=413 nm). An increase of two orders of magnitude in the ionization efficiency is found favoring the transition at 553 nm. This technique can be implemented using commercial all-solid-state laser systems and is expected to be advantageous compared to other narrowband photo-ionization schemes of barium in cases where highest efficiency and isotope-selectivity are required.     

Measurement of the lifetime and quenching rate of metastable 2S muonic helium ions

The lifetime of the 2S state in (μ^?4He)⁺ ions has been measured at He-gas pressures between 50 Torr and 6 atm (T=300 K). We observed both X-rays from the two-photon 2S→1S transitions as well as delayed K_α X-rays associated with radiative quenching. The quenching rate is strongly pressure dependent; it is predominantly a quadratic function of pressure with a measured three-body rate coefficient k=(5.9±0.8)×10^?32cm⁶/s. At 6 atm, we find τ_2S<250 ns because of the absence of two-photon transitions.