Structural and dynamical properties of aqueous suspensions of NaPSS (HPSS) at very low ionic strength

Results on the structural and dynamical properties of aqueous solutions of NaPSS (HPSS) are reported. Most samples of previous measurements, including our own, are contaminated by the presence of (temporal) aggregates. The emphasis of this paper lies on investigations of well purified samples at very low ionic strength where interacting effects are maximum. As previously reported, this can be achieved by pumping the suspension through ion exchange resin by means of a tube-pump, using filters of pore size. Information has been extracted from static and dynamic light scattering and viscosity measurements. A second maximum is observed in the scattering curves versus wavenumber for the first time. It is discussed on the basis of two current models describing the structure of charged macromolecules. The short time dynamics reflects the measured intensity. Detailed viscosity data in comparison of those of rodlike (TMV), slightly flexible so-called fd virus particles (length 880 nm) are used to confirm the interpretation of the light scattering results. The recently observed maximum in the reduced viscosity could be confirmed. Received: 5 May 1997 / Revised: 1 September 1997 / Accepted: 10 November 1997     

Towards optical spectroscopy of the element nobelium ({\sf Z }= \mathsf{102}) in a buffer gas cell

For the investigation of the atomic level structure of heavy elements which can only be produced at on-line facilities such as GSI, a novel experimental procedure has been developed. It is based on Radiation Detected Resonance Ionization Spectroscopy (RADRIS) and can be applied to elements like nobelium produced at rates of a few ions per second. Fusion reaction products are separated from the primary beam by the velocity filter SHIP at GSI, stopped in a buffer gas cell, collected on a tantalum filament and then re-evaporated as atoms. The ions produced by resonance ionization with tunable laser beams are detected via their characteristic α decay. First on-line experiments on α-active ¹⁵⁵Yb, which is supposed to have an atomic level structure similar to nobelium, were performed. These test experiments focused on the optimization of the collection and re-evaporation process of the radioactive ions, the laser ionization efficiency and the detection via α decay. An overall efficiency for RADRIS of 0.8% with respect to the target production rate was measured. While further improvements of this efficiency are in progress it should already be sufficient for the search for atomic levels in nobelium.     

Prospects of ion-mobility measurements in superheavy element research

The element specific electron configuration of ions directly reflects the two quantum mechanical observables 〈r²〉 and r_max, which denote the r² expectation value of the electron density and the principle maximum of the wave function of the outermost electron orbital, respectively. Thus, the determination of these observables may present a new access to element identification of single superheavy nuclides. In this paper, we discuss how these observables are related to ionic radii deduced from ion-mobility data using the most simple hard sphere model and semi-empirical (n,6,4) model potentials for the interaction of heavy ions with noble gases. A concept for a high resolution ion-mobility spectrometer is presented. Optimum extraction efficiency of the ions will be achieved by decoupling the ion motion from the electric field drift by the friction force of the suitably shaped gas flow at the exit nozzle.     

Ion traps --Precision measurements and more

Today ion traps are an important experimental tool. Applications range from high-precision measurements of masses and moments, realization of atomic clocks, to the study of ion chemical reactions. Ion traps have gained particular importance in the field of nuclear physics where they are used for the precise determination of nuclear binding energies, decay studies, and radioactive ion beam manipulation. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: bollen@nscl.msu.edu     

Molecular invariants: Atomic-group valence

Summary In this work, a generalized valence is defined for an atomic group; it reduces to the known expressions for the case of an atom in a molecule. It is the sum of the correlations between the fluctuations of the atomic chargesq _C andq _D (C belongs to the group andD does not) around their average values. Numerical results agree with chemical expectation.     

Cooling,identification and spectroscopy of super-heavy element ions

We briefly discuss some possibilities for cooling, identification and spectroscopy of super-heavy element (SHE) ions based on recent results obtained from studies of atomic and molecular ions in linear rf traps. Since these investigations only relied on the charge and the mass of the ion of interest, we believe it should be straight forward to adopt most of the techniques for SHE ion research.     

Nuclear spins, magnetic moments and α-decay spectroscopy of long-lived isomeric states in 185Pb

Alpha-decay properties of the neutron-deficient isotope ¹⁸⁵Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast to previous studies, two α-decaying isomeric states were identified in ¹⁸⁵Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were interpreted as 3/2^- and 13/2⁺ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the I ^π = 13/2⁺ isomer are E _α = 6408(5) keV, T _1/2 = 4.3(2) s, respectively; while for the I ^π = 3/2^- isomer ( T _1/2 = 6.3(4) s) two α-decays with E _α1 = 6288(5) keV, I _α1 = 56(2)% and E _α2 = 6486(5) keV, I _α2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope ¹⁸¹Hg was obtained. Received: 7 February 2002 / Accepted: 19 February 2002     

Advanced Mechanics and General Relativity,by J. Franklin

Ion Coulomb crystals, formed by atomic ions at low temperatures in radiofrequency and Penning ion traps, are structures that have remarkable properties and many applications. Images of Coulomb crystals are striking and reveal the crystal structure, which arises from a balance between the trapping forces acting on the ions and their mutual Coulomb repulsion. Applications of these structures range from frequency standards and quantum simulation through to measurement of the cross-sections of chemical reactions of ions.     

稀土掺杂对钴铁氧体电子结构和磁性能影响的理论研究

尖晶石型铁氧体是十分重要的磁性材料之一, 具有独特的物理性质、化学特性、磁学特性和电子特性. 其中尖晶石型钴铁氧体具有较好的电磁性质而被广泛应用. 本文基于密度泛函理论(DFT) 的第一性原理平面波赝势法, 结合广义梯度近似(GGA+U), 研究了CoRE_0.125Fe_1.875O₄ (RE = Nd, Eu, Gd)体系的电子结构和磁性能. 结果表明随着稀土元素从Nd到Gd掺杂体系晶胞的晶格常数呈递减趋势. 磁性能依赖于稀土离子(RE³⁺)4f轨道未配对的电子数, 掺杂Eu和Gd能够提高钴铁氧体体系的磁矩, 主要因为它们3+价态离子具有较多未配对的4f电子, 因而对磁性能的影响较大. 然而Nd 的掺杂对体系磁性能的影响很小, 这是由于它的离子半径较大, 导致晶格发生畸变.     

Electronic properties of Pb(ZrTi)O3 solid solutions

The theoretical backgrounds and some experimental data on the electronic properties of polycrystalline Pb(Zr, Ti)O₃ solid solutions are summarized. These substances occur in the perovskite structure, and so their electronic band structure is presumed to be analogous to other perovskite compounds. Their forbidden gap energy has been determined to be about 3.30–3.56 eV on the basis of optical, photoacoustical, and photoelectrical measurements. Many local levels and traps exist in the forbidden gap because of the polycrystalline character and heterovalent doping. Their actual configurations and states strongly influence the optical, photoelectrical, piezoelectrical, and other physical properties of Pb(Zr, Ti)O₃ solid solutions.     

Relativistic Calculations for Trapped Ions

We present recent results in the field of total binding energy calculations, Landщ factors, quantum electrodynamics corrections and lifetime that are of interest for ion traps and ion sources. We describe in detail MCDF and RMBPT calculation of ionic binding energies, which are needed for the determination of atomic masses from highly charged ion measurements. We also show new results concerning Landщ factor in 3-electron ions. Finally we describe how relativistic calculations can help understand the physics of heavy ion production ion sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

TITAN: an ion trap for accurate mass measurements of ms-half-life nuclides

The introduction of Paul traps, in particular linear radio-frequency quadrupoles in the early 2000s, has revolutionized the use of ion traps for probing the properties of radioactive nuclides. It opened the path to trapping all available nuclides, independent of their chemical properties. We present an overview of direct mass measurements of short-lived nuclides using TITAN, a Penning trap mass spectrometer facility particularly suitable for precision measurements of ms-half-life nuclides.     

Extended Hubbard model with renormalized Wannier wave functions in the correlated state: beyond the parametrized models

The method used earlier for analysis of correlated nanoscopic systems is extended to infinite (periodic) s-band-like systems described by the Hubbard model. The optimized single-particle Wannier wave functions contained in the parameters of the extended Hubbard model (in the nearest-neghbor hopping (-t), in the magnitude of the intraatomic interaction U, and in other parameters) are determined explicitly in the correlated state for the electronic systems of various symmetries and dimensions: Hubbard chain, square and triangular planar lattices, and the three cubic lattices (SC, BCC, FCC). In effect, the evolution of the electronic properties as a function of interatomic distance R is obtained. The model parameters in most cases do not scale linearly with the lattice spacing and hence, their solution as a function of microscopic parameters reflects only qualitatively the system evolution. Also, the atomic energy changes with R and therefore should be included in the model analysis. The solutions in one dimension (D = 1) can be analyzed both rigorously (by making use of the Lieb–Wu solution) and compared with the approximate Gutzwiller treatments. In higher dimensions (D = 2 and 3) only the latter approach is possible to implement within the scheme. The renormalized single particle wave functions are almost independent of the choice of the scheme selected to diagonalize the Hamiltonian in the Fock space in D = 1 case. For dimensions D > 1 the qualitative behavior is independent of the structure considered. The wave-function size increases above the Mott-Hubbard localization threshold and gradually reaches the atomic limit value. The method can be extended to other approximation schemes, as stressed at the end.     

Chemical and catalytic effects of ion implantation

Energetic particles are used for inducing chemical reactions as well as for modifying the properties of materials with regard to their bulk and surface chemical behavior. The effects are partly caused by radiation damage or phase intermixing, partly by the chemical properties of the individual bombarding particles. In this contribution a survey of relevant applications of these techniques is presented:

1) Chemical reactions of implanted and recoil atoms and their use for syntheses, doping and labeling of compounds.

2) The formation of thin films by decomposing chemical compounds with ion beams.

3) Catalytic effects on substrates treated by sputtering or ion implantation. Recent results with nonmetallic substrates are reviewed. Mainly hydrogenation reactions at a solid/gas interface or redox reactions at an electrified solid/liquid interface are mentioned.

The present status and future prospects of these kinds of investigations will be discussed.     

The mobility of the amorphous phase in polyethylene as a determining factor for slow crack growth

Polyethylene (PE) pipes generally exhibit a limited lifetime, which is considerably shorter than their chemical degradation period. Slow crack growth failure occurs when pipes are used in long-distance water or gas distribution though being exposed to a pressure lower than the corresponding yield stress. This slow crack growth failure is characterized by localized craze growth and craze fibril rupture. In the literature, the lifetime of PE pipes is often considered as being determined by the density of tie chains connecting adjacent crystalline lamellae. But this consideration cannot explain the excellent durability of the recent bimodal grade PE for pipe application. We show in this paper the importance of the craze fibril length as the determining factor for the pipe lifetime. The conclusions are drawn from stress analysis. It is found that longer craze fibrils sustain lower stress and are deformed to a lesser degree. The mobility of the amorphous phase is found to control the amount of material that can be sucked in by the craze fibrils and thus the length of the craze fibrils. The mobility of the amorphous phase can be monitored by dynamic mechanical analysis measurements. Excellent agreement between the mobility thus derived and lifetimes of PE materials as derived from FNCT (full notch creep test) is given, thus providing an effective means to estimate the lifetime of PE pipes by considering well-defined physical properties.     

Study of (Al2O3)n(Ox) clusters with n = 16 and x = 0, 1, 2 from first principles calculations

The ionic and electronic structure of (Al₂O₃)_n(O_x) clusters with n 16 and x = 0, 1, 2 is studied by means of first principles density functional calculations, norm-conserving pseudopotentials and a numerical atomic basis set. The equilibrium geometries have been determined by total energy minimization, starting with several initial geometries for each cluster size. The trends obtained for the atomic arrangements (structural isomers, coordination numbers, disordered versus ordered structures, etc.) and the electronic properties (binding energies, Homo-Lumo gap and dipole moments) are discussed. For most of the oxidized clusters studied here we find that the Homo-Lumo gap and the magnitude of dipole moment of isomeric species can vary drastically.     

Small polaron formation in many-particle states of the Hubbard-Holstein model: The one-dimensional case

We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless phonons of frequency . Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case , the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime overcomes the energy of the purely electronic system . In the antiadiabatic case, , polaron formation is instead driven by the condition of a large ionic displacement (g being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes are also analyzed. Received 15 February 1999     

High-precision mass measurements of hydrogen-like <Superscript>24</Superscript>Mg<Superscript>11+</Superscript> and <Superscript>26</Superscript>Mg<Superscript>11+</Superscript> ions in a Penning trap

For the determination of the bound-electron g factor in hydrogen-like heavy ions the mass of the ion is needed at a relative uncertainty of at least 1 ppb. With the SMILETRAP Penning trap mass spectrometer at the Manne Siegbahn Laboratory in Stockholm several mass measurements of ions with even-even nuclei at this level of precision have been performed so far, exploiting the fact that the mass precision increases linearly with the ion charge. Measurements of masses of the hydrogen-like ions of the two Mg-isotopes ²⁴Mg and ²⁶Mg are reported. The masses of the hydrogen-like ions are 23.979011054(14) u and 25.976562354(34) u, corresponding to the atomic masses 23.985041690(14) u and 25.982592986(34) u, respectively. The possibility to use these two isotopes for the first observation of an isotope effect in the bound-electron g factor in hydrogen-like heavy ions is discussed.     

Stabilization of catalytically active gold species in Fe-modified zeolites

The influence of iron additive on redox, electronic and catalytic properties of gold incorporated into zeolite catalysts has been studied by means of TEM, XPS, XRD, TPR, ICP and AES. The interaction of gold with iron modifier was observed in Y-zeolites and mordenites with different cations and method of Fe incorporation (impregnation or ion exchange). This interaction leads to mutual influence on redox properties of Fe and Au ionic species and facilitates their reduction. Limited diffusion of Au precursor after Fe species deposition in narrow mordenite channels does not permit to incorporate Au in adequate concentration, while in large super-cage of Y-zeolites this limitation is absent. The structure of Y-zeolites favors formation of active gold species. Catalytic tests in CO oxidation show that Fe additive stabilizes the gold active species active at low-temperature (partly charged clusters) and makes them insensitive to redox treatments.     

Non-partial-wave Coulomb-Born theory for the excitation of many-electron atomic ions II: Numerical description and application

A non-partial-wave Coulomb-Born theory is recently formulated to treat the excitation of many-electron atomic ions for impact by an arbitrary charged particle [Y.B. Duan et al., Phys. Rev. A 56, 2431 (1997)]. The multiple expansion of the transition matrix element is decomposed into the target form factor and the projectile form factor. These are the matrix elements of the tensor operators between quantum states so that any complicated wave function for the target ion can be employed. In this formal theory, an infinitesimally small positive quantity is introduced artificially to guarantee the convergence of integrals. As a supplementary part of the theory, we discuss how to choose the value of . It is found that the should be taken as functions of the momentum transfer and multipolarity . Illustrations are carried out by calculating the cross-sections for some typical transitions n _a l _a -n _b l _b of hydrogen-like ions for impact by electron, positron, and proton, respectively. The resulting cross-sections are in good agreement with ones produced by using a method available for ion targets with Slater-type orbitals [N.C. Deb, N.C. Sil, Phys. Rev. A 28, 2806 (1993)]. Comparisons demonstrate that the Coulomb-Born theory with non-partial wave analysis provides a powerful method to treat the excitation of many-electron atomic ions impact by an arbitrary charged particle. Received 6 April 1999