Snowballs of radioactive ions — nuclear spin polarization of core ions

Short-lived ions¹²B (beta-radioactive, T_1/2=20.3 ms) sustaining nuclear spin polarization were introduced into superfluid helium at 1.7 K. It was found that the¹²B ions were transported as charged entities under a static electric field and that the nuclear polarization was maintained throughout the lifetime of¹²B nuclei. Polarization of¹²B was determined through beta-NMR method. Snowball, a singly charged microcluster of helium atoms formed around an impurity ion, is responsible for the behaviour and thus constitutes a suitable environment for preserving nuclear polarization of the core ions¹²B. In a separate experiment snowballs were produced by implanting⁸Li (T_1/2=830 ms) into liquid helium and detected by means of alpha particles from the core ions to guarantee that the snowballs survive longer than the lifetime of¹²B.     

OH− ions in Oxide Crystals

This article reviews the spectroscopic properties of hydrogen bound to a large variety of synthetic compounds like simple oxides, perovskites, the LiNbO₃ family, KTP, sillenites, eulytites, borates, garnets, spinels and some others. In almost all compounds the OH stretch mode is found in the range 3200-3700 cm^?1, with isotope replica of deuterium (2350-2750 cm^?1) and a few examples of tritium (2050-2250 cm^?1). The fundamental vibration, the isotope replica and the corresponding overtones are described with an anharmonic oscillator model. A nonlinear relation between the anharmonicity and the harmonic frequency is found and interpreted using recent second order perturbation calculations. An often pronounced temperature dependence of the stretch mode and phonon coupling is discussed. Data for the stretching vibration influenced by additional weak or strong doping are presented. Atomistic defect models are described and tested by means of light polarization, external perturbations like pressure and electric field, and Raman scattering analyzed with the behavior-type method. The last section briefly reviews applications profiting from doping with hydrogen and its easy detection by means of the OH stretch mode.     

Towards sympathetic cooling of trapped ions with laser-cooled Mg + ions for mass spectrometry and laser spectroscopy

Sympathetic cooling by laser cooled Mg ions has been proposed as a method for fast cooling of highly charged ions to a very low temperature. The paper describes the construction of the solid state laser system at 279.63 nm required for laser cooling of the Mg ions. The laser system is composed of a fiber laser at 1,118.54 nm and two successive second harmonic generation (SHG) ring cavities for frequency quadrupling. In the first SHG cavity, non-critical phase matching of a lithium triborate (LBO) crystal is used for doubling from 1,118.54 to 559.27 nm. The second SHG cavity uses critical phase matching of a β-barium borate (BBO) crystal for doubling from 559.27 to 279.63 nm. With the aid of Boyd–Kleinmann theory, optimum experimental parameters are calculated and used for an efficient SHG. Besides this, the paper intends to be a shortcut for practical applications of the Boyd–Kleinmann theory for SHG.     

Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-π interactions

Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-π interactions. The key to this cation-π interaction is the coupling of the delocalized π states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.     

Kβ X-ray emission from He-like ions

Relativistic calculations on the energies and electric dipole rates of K_β X-rays from 1s3p(¹P₁,³P₁)-1s² (¹S₀) transitions for He-like ions in the range Z=14–54 are carried out using multi-configuration Dirac–Fock (MCDF) wave functions in the active space interaction approach. The contributions from Breit interaction and quantum electrodynamics have also been included in the calculation. An attempt has been made to find a scaling expression for Breit energy in terms of Zα .The scaled Breit energies are in good agreement with the earlier accurate relativistic results and this ensures the reliability of our scaling procedure. The behavior of MCDF wavefunctions for a given J in the non-relativistic limit has also been studied. The calculated K_β X-ray energies and rates agree well with other available experimental and theoretical values.     

Quasichanneling of ions in crystals. I. Elastic scattering of ions on atomic “chains” and planes

The scattering of quasichanneled particles on atomic chains and planes is studied by computer simulation for the crystals of chemical compounds. It is shown that quasichanneling is the specific regime of ion motion in the lattice. Its main features are: (1) a sharp increase of the backscattering probability; (2) transition of the ions from the quasichanneled component into a random one; (3) high sensitivity to the structure and the composition of the atomic “chain”; (4) dependence on the value and the direction of the atomic displacements.     

Substitution mechanism of Zn ions in β-tricalcium phosphate

Zn-doped β-tricalcium phosphate (β-TCP) is synthesized by the solid-state reaction method. The substitution mechanism of Zn ions in β-TCP synthesized here is investigated by carrying out a combination of near-edge X-ray absorption fine structure (NEXAFS) measurements and first-principles calculations. From the results of the present study, the substitution site for Zn ions in β-TCP is successfully determined.     

Electron-stimulated desorption of positive ions from hexagonal α-SiC

Electron-stimulated desorption (ESD) of positive ions (H⁺, O⁺, ⁺OH, F⁺ and Cl⁺) from the Si- and C-terminated surfaces of hexagonal α-SiC has been observed for electron energies in the 5–105 eV range. Comparison of these results with those for the ESD of the same ions from the surfaces of Si and condensed hydrocarbons leads to a model for the H⁺, ⁺OH, F⁺ and Cl⁺ threshold desorption process based on transitions from deep valence Si and C “s-like” levels to states in the conduction band, followed by Auger decay to form a localized multiple valence-hole configuration. O⁺ desorption, on the other hand, is initiated by O 2s ionization. Evidence is found for a strong dependence of the F⁺ threshold on the local chemical bonding. The results indicate that the thresholds for ESD of these ions from SiC are determined more by the electronic excitation of the substrate than by direct excitation of the adsorbate bond.     

Coulomb predissociation rates of He dµ molecular ions

The predissociation or particle emitting decay rates of muonic molecular ions³He dµ and⁴He dµ are estimated by means of the complex rotation method. We use a highly accurate variational three-bodyP-wave function based on random-tempered Slater-type exponential expansion. A resonance eigenvalue ofE=–48.420 89 eV and =0.348 × 10^–3 eV for the³He dµ ion and a resonance eigenvalue ofE=–58.225 303 eV and =0.118 × 10^–3 eV for the⁴He dµ ion have been obtained. These results are in a good agreement with the ones previously obtained by Kino and Kamimura by scattering calculation with the non-adiabatic coupled-rearrangement-channel method.     

Collision dynamics between heavy ions determined from δ-electron spectra

The δ-electron spectra from binary dissipative PbPb collisions at 8.6 MeV/u incident energy exhibit the influence of an interference pattern due to time delay caused by nuclear contact. A model-independent analysis of these δ-electron spectra is developed to yield the mean trajectories of the colliding nuclei.     

X-ray emission via Kα resonance complexes in gold ions

The excitation energies from ground state for 63 fine structure levels of the terms belonging to 1 s², 1snl, 2lnl′ (n = 2,3), 3l3l′ (l ≠ ≠ l′) configurations of Au⁷⁷⁺, as well as oscillator strengths for electric-dipole-allowed and intercombination transitions among the fine-structure levels were theoretically evaluated. The important relativistic effects in intermediate coupling are incorporated by means of the Breit–Pauli Hamiltonian. Extensive comparisons are performed with several approximations and previous data sets in order to size up contributing effects and to estimate accuracy ratings. The atomic excitation is obtained by electron impact in close coupling approach. For optically allowed transitions, the electron-impact collision strengths at collision energy up to 80 keV are reported. The results are relevant to the laboratory and astrophysical plasmas.     

Theoretical study of LiCl− and LiBr− molecular ions

The molecular structures and spectroscopic constants of the ground electronic states of LiCl^? and LiBr^? are investigated with the coupled-cluster method. To improve the accuracy of our calculations, we have employed the extrapolation schemes as well as corrections of the core–valence correlation and scalar relativistic effect. The equilibrium parameters, potential energy curves, force constants, vibrational energy levels and spectroscopic parameters of both molecular ions are derived, in which those of LiBr^? are reported for the first time. The electron affinities and vertical detachment energies of neutral and anionic LiCl and LiBr are also evaluated.     

Loss of electrons by fast H− ions in gases

The characteristic angles and cross sections for a (\mathop 1^- 0) + (\mathop 1^- 1)(\mathop 1\limits^ - 0) + (\mathop 1\limits^ - 1) reaction in which H⁻ atoms with an energy of 0.1–10 000 MeV lose electrons when scattered on C, N, or O atoms were calculated for the relativistic case of the Bethe scattering theory. The cross sections for N₂, O₂, and CO₂ molecular targets were obtained using the additivity rule. The results presented are compared with known experimental and theoretical data.     

k-quantum nonlinear Jaynes－Cummings model in two trapped ions

We have obtained a k-quantum nonlinear Jaynes－Cummings model for two trapped ions interacting with laser beams resonant to the kth red side-band of the centre-of-mass mode, far from the Lamb－Dicke regime. The exact analytic solution shows the existence of quantum collapses and revivals of the occupation of two atoms.     

Preparation and optical spectroscopy of phosphate glasses containing divalent europium ions

P2O5.BaO.Na2O.K2O glasses doped with various content of Eu2O3 were prepared using high temperature melting method, and the Eu2+ ions in the phosphate glasses were obtained with the aid of the reductive action of silicon powder. The fabricating conditions, fluorescence, excitation spectra of the glasses were then studied. The glasses containing europium show a broad emission band at 450 nm and sharp bands from 580 to 650 nm, and the co-existence of Eu2+ and Eu3+ is identified. Also, a good glass with a dominant proportion and large quantity of Eu2+ ions can be obtained by the reductive action of silicon powder and proper processing.     

Materials modification at zirconium–silicon interface using swift heavy ions

The reactivity of the Zr/Si interface induced by swift heavy ion beams of Au has been investigated in the present work. Zirconium was evaporated on a clean silicon substrate in ultra high vacuum (UHV) at a pressure of 10^?8 Torr by the electron beam evaporation technique and the final layer was a thin film of Au to avoid oxidation of zirconium. The Zr/Si system was irradiated by 350 MeV Au²⁶⁺ ions at liquid nitrogen temperature at different fluences (0.46×10¹⁴, 1.85×10¹⁴ and 4.62×10¹⁴ ions/cm²). Rutherford back scattering (RBS) spectroscopy using 2 MeV He ions was used to monitor the Zr and Si concentration profiles and interdiffusion at the interfaces. The irradiation at the Zr/Si interface showed mixing. X-ray diffraction measurements confirmed the formation of the ZrSi₂ phase. Thermal spike formation and melting in the tracks was found to be the dominant process at the interfaces.     

Spectral studies on Cu ions in sodium–lead borophosphate glasses

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cu²⁺ ions in sodium–lead borophosphate glasses doped with different concentrations of Cu²⁺ ions have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in sodium–lead borophosphate glasses are present in octahedral sites with tetragonal distortion. The optical absorption spectra of all the glass samples show a single broad band, which has been assigned to the ²B_1g→²B_2g transition of Cu²⁺ ions. The optical band gap energy (E_opt) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. The emission bands observed in the ultraviolet and blue region are attributed to 3d⁹4s→3d¹⁰ triplet transition in Cu⁺ ion. The FT-IR spectra show that the glass system contains BO₃, BO₄ and PO₄ structural units.     

Energetical structure of muonic molecular ions ddµ and dtµ

The long-lived states lying below then=2 threshold in muonic molecular ions ddµ and dtµ are reviewed. We have considered all the known long-lived states both of normal and anomalous spatial parity, the bound states as well as resonant three-body states of shape and Feshbach types. It is shown that these states could be satisfactorily classified in terms of the Born-Oppenheimer adiabatic theory. We calculate some characteristic properties of the Feshbach resonances, thus obtaining that the life-time of the 3d states is greater than 10^–11 s, and the fusion rate from these states less than 10⁹ s^–1. The geometry of the 4f(J=0,v=0) state shows that it does not obey approximate ungerade symmetry. On the contrary, the low vibrational 3d states are approximately of gerade symmetry, as a result these states decay ejecting dµ atoms in the same proportion as tµ atoms.     

Dielectronic recombination rates for ions of the magnesium sequence—II

The dielectronic recombination (DR) rate coefficient α^DR is explicitly calculated for Ar, Fe and Mo target ions of the Mg isoelectronic sequence (12 electrons). The 2p transitions are dominant at high temperatures and are considered in detail with full LS coupling. This work extends our previous study in which both the 3s, Δn = 0 and 3s, Δn ≠ 0 transitions are considered. Scaling of α^DR with free-electron temperature is also discussed.     

Detection of parametric resonance of trapped ions for micromotion compensation

We have detected excess micromotion of trapped ions by modulating the trapping voltage. This radio-frequency (rf) modulation induces parametric resonance and excites secular motion of the trapped ions when they possess excess motion. This technique has been applied to laser-cooled ions in a linear rf trap and it provides optimum values for compensating the trapping field. We found that the technique has sensitivity equal to or greater than the conventional method for detecting excess micromotion. Because any laser propagation direction can be used, this method is expected to be applied to surface-electrode traps.