Electromigration of copper in lead

The electromigration of copper in lead was measured under isothermal conditions by a steady-state method. ⁶⁴Cu was introduced into the lead solvent as a radioactive tracer solute. After electromigration, the steady-state, concentration-distance curve was determined by standard sectioning, weighing and counting techniques. Although the experiments extend from 215 to 303°C, the measurements for Z¹, the effective charge number for copper in lead, appear to show at low temperature a strong dependence on concentration and are also difficult to reproduce satisfactorily in this temperature range. Accordingly only the results in the range from 240°C and up have been included in calculating the electromigration parameters. These results give Z¹ in the range 1.1 ± 0.3 and indicate an electrostatic charge, Z_el, of 1,8 ±0.9.     

A study of electromigration of nickel in lead

The steady state method was used to study the electromigration of ⁶³Ni in Pb. For the temperature range 180–290°C, and Ni concentration range 0.1–1000 ppm, Ni migrates toward the anode. For dilute samples (0.1 ppm Ni) the effective charge varies linearly with the inverse resistivity from ?6.75 at 188°C to ?4.97 at 289°C. The 1/ρ dependence is given by $\text{Z1 = (1.4 ± 0.3)?(288 ± 13)× 10}{}^{\mathrm{?6}}\text{/ρ}$. The effective charge is a function of the Ni concentration, increasing in magnitude with increasing concentration. For 1000 ppm Ni, |Z1| exhibits a sharp maximum around 260°C; below 230°C electromigration takes place at a much slower rate, probably due to precipitation.     

Electromigration of gold (high concentration) in lead

The steady state method was used to study the electromigration of ¹⁹⁵Au in lead doped with 680 ppm Au. In the temperature range 165–270°C Au migrates toward the anode, as in the case of more dilute solutions; but the effective charge increases in magnitude with decreasing temperature at a faster rate than that observed for dilute Pb(Au) samples, so that the difference between the effective charge for the 680 ppm samples and that for dilute samples becomes larger as the solubility limit is approached. A simple model, which allows for formation of Au doublets in equilibrium with the singlets, predicts an apparent increase of Z¹ with concentration of impurity at lower temperatures somewhat greater than the observed effect.     

Self-similarity of nonlinear screening in asymmetric complex plasmas

In this paper, two-component electroneutral systems of finite-sized macroions and oppositely charged point-like microions in the average spherical electroneutral Wigner–Seitz cell with a central macroion are studied. We investigate the self-similarity of nonlinear screening of highly charged macroions by microions in a classical asymmetrically charged complex plasma. This work is devoted to the problem of the relationship between the effective (‘visible’) charge of the macroion Z^* and its initial charge Z taking into account the effect of the nonlinear screening. It is analysed how the form of the dependence Z^*(Z) changes. The self-similarity of this dependence has been demonstrated for various characteristic system temperatures, macroion concentrations, and macroion sizes.     

X ray spectroscopic intercomparison between hydrogenic ions of different Z as a method for determining Lamb shifts

Novel methods for determining the 1s Lamb shift of hydrogenic ions are outlined. In one method the energy of a 2–1 transition in the hydrogenic ion of nuclear charge Z is compared to a 4–2 transition in the hydrogenic ion of charge 2Z. A second method exploits close coincidences between Lyman series transitions in ions of similar Z. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of exotic atoms by direct capture and via transfer from hydrogen

Exotic atoms like muonic atoms can be formed either by direct capture, often called Coulomb capture, or by muon transfer from a muonic hydrogen atom. The first estimates for the formation predicted, for both mechanisms, probabilities approximately proportional to the charge numberZ. The experiments did not confirm such a simpleZ-dependence. In direct capture, it turned out that the chemical bond played a decisive role, at least for lighter elements. In the formation via transfer, surprising data were obtained not only for heteroatomic molecules but also for noble gases. Whereas for direct capture, a model is able to reproduce quite satisfactorily a great number of measured capture ratios, including those in hydrogen compounds, the formation via transfer seems to put completely different and more fundamental questions.     

Effect of collision-induced phase-shifts on the line widths and line shifts of CO2-Ar system

The theoretical calculation of line widths and line shifts for CO₂-Ar system is computed by the Mehrotra-Boggs theory. It is shown for this system that the phase shift effect is very important at large values of |m| wherem is the value of rotational quantum numberJ in the lower vibrational state. It is also pointed out that the Salesky-Korff theory is the same as the Mehrotra-Boggs theory.     

Aerosol Charge Neutralization by a Radioactive Alpha Source

The performance of a Po-210 radioactive ionizer for aerosol charge neutralization and bipolar charging has been evaluated. Monodisperse neutral and singly charged aerosols have been passed through the ionizer and their approach to the steady-state Boltzmann charge measured by measuring the fraction of particles that are electrically charged. The result shows that an Nt of approximately 2.5 × 10⁵ cm^?3 s is needed for the development of a steady-state charge fraction equal to that given by the Boltzmann' s law where N is the ion concentration and t is the residence time of the aerosol in the neutralizer. In addition, the performance of the ionizer for particle charge neutralization in a vibrating-orifice aerosol generator has been evaluated and the result shows that the source is less effective for this application and the residual charge on the particles is considerably higher than that given by the Boltzmann's law.     

Mass absorption coefficients and range of beta particles in Be,Al, Cu,Ag and Pb

It is demonstrated that the practical range of a beta spectrum (E _max=E) in any material can be obtained from mass absorption coefficient (μ/ρ) values. It is further shown that a semiempirical relation likeμ/ρ =AE ^−B in whichA andB are related to the atomic numberZ, of the absorber can be used for determiningμ/ρ of any material of known atomic numberZ. Theβ particle ranges are compared with theoreticalcsda and practical ranges from literature.     

Effect of direct electric current on phase formation in Pb-Sn liquid-solid alloys

The effect of a constant electric current on the phase state of alloys of the lead-tin system in the liquid-solid state was investigated. It was shown that solid inclusions are displaced to one of the electrodes according to the effective charge (particles Z* > 0 are transferred to the cathode, while particles Z* < 0 are transported to the anode).     

Approximate normalized wave functions for the finite-size Coulomb problem

Using perturbation methods developed previously for the finite-size energy shift, thes-state wave functions for a bound lepton in the Coulomb field of a nucleus with an arbitrary charge distribution are developed through order (Zα)². This technique allows a determination of the finite-size contribution to the normalization of the wave function up to order (Zα)², both for small separations of the lepton and nucleus and for the lepton outside the nucleus. General features of the wave function are discussea, including the transition of the Dirac problem to the (singular) point charge limit. A practical application is developed using these results.     

Radial scanning diagnostics of bremsstrahlung and line emission in T-10 plasma

The paper describes the scanning spectroscopic diagnostics designed for measurement of line integrated plasma radiation in two visible spectral ranges. This diagnostic system is aimed at measuring the bremsstrahlung absolute values and profile with high spatial resolution. The bremsstrahlung absolute values are used to determine the value and radial distribution of effective plasma ion charge Z _eff(r) in T-10 discharges. The importance of Z _eff measurement is due to its strong influence on plasma heating, confinement, and stability. The spatial distribution of emission for one of the chosen spectral lines is measured simultaneously with bremsstrahlung. The spatial resolution of measurements is ~1 cm, and the temporal resolution is up to 10 ms. The spectral equipment and methods for its calibration are described. Examples of line integrated brightness distribution in a “continuum window” of 5236 ± 6 Å and brightness of the lines C⁵⁺ (5291 Å), He¹⁺ (4686 Å), and D_β (4861 Å) are given. Flattening of the bremsstrahlung brightness profile in the central region of the plasma column in some discharges with sawtooth oscillations in the T-10 is observed. The measured effective ion charge profiles in ohmic discharges with high plasma density and low discharge currents demonstrate accumulation of light impurities at the column axis; as a consequence, quenching of sawtooth oscillations in some discharges is observed. The developed diagnostics provides necessary data for investigation of heat, particle, and current transport in the plasma of the T-10. Successful application of the obtained data on Z _eff(r) for investigation of geodesic acoustic modes of plasma oscillations in the T-10 should be specially noted.     

Magic numbers and low energy nuclear transmutation by protons in host metals

The observed nuclear transmutations by protons or deuterons in host metals at low reaction energies are evaluated. Reaction probabilitiesN(Z) depending on the atomic numberZ show maxima close to the magic numbers with the exception ofZ=20. The exponential decay of the maxima onZ have an incrementZ′=10. Exactly this empirically derived relation fits a sequence of the magic numbers of 3 ⁿ , where the basis value 3 reminds of the threefold scheme of the quarks. Dedicated to Prof. Dr. D. Sc. Drs. h.c. Arthur Sharmann to his 70th birthday, 26 January 1998.     

Determination of the effective nuclear charge from EPR data using a modified crystal-field theory

We propose a scheme for determining the effective nuclear charge Z _ef^CF of a 3d ion placed in a crystal field of arbitrary symmetry. As an example, we consider the Co²⁺ ion in a matrix MCO₃ (M = Ca, Cd). We show that the effective nuclear charge Z _ef^CF correlates with a change in the degree of the bond covalence.     

Beta-decay of nuclei near the neutron shell <Emphasis Type="Italic">N</Emphasis> = 126

A self-consistent approach to the weak interaction rates is presented. It is based on the generalized energy-density functional method and continuum QRPA. The study has been made of the β-decay total energy releases, half-lives and β-delayed neutron emission branchings for recently identified near-spherical nuclei with charge numbers Z = 76–79 approaching the closed neutron shell at N = 126. Together with our previous calculations near N = 28, 50, 82 this provides an important update to the standard set of weak rates for the r-process modeling, radioactive beam experiments and advanced reactor applications. Within the fully microscopic framework a significant competition is found of the Gamow-Teller and first-forbidden decay contributions to the total half-lives.     

On the possible role of the bootstrap effect in the RF current drive experiments

Conditions of existence of the bootstrap effect at anomalous diffusion in tokamaks are discussed. Assuming that these conditions are fulfilled at lower hybrid current drive, various models of anomalous diffusion and of temperature profiles are considered. Toroidal current density profiles and related quantities are calculated, demonstrating strong dependences on the electron temperature profiles and on the effective ion charge Z_eff. Recommendations for experimental revealing the bootstrap current are presented.     

High Z effects in accounting for radiative component of the electron magnetic moment in hydrogen-like atoms

The behavior of electron energy levels in hydrogen-like atoms is studied while taking into account the nonperturbative interaction between the radiative component of the magnetic moment of a free electron Δg _free and the Coulomb field of an atomic nucleus with charge Z, including those with Z > 137. It is shown that for Zα ? 1 the energy-level shift is rather effectively determined through the matrix elements of the corresponding Dirac-Pauli operator with relativistic Coulomb wave functions. At the same time, for superheavy nuclei with Z ～ 170, this shift, generated by Δg _free, is genuinely nonperturbative, behaves like ～Z ⁵ near the threshold of negative continuum, exceeds all the estimates of radiative corrections coming from vacuum polarization and electron self-energy known so far, and turns out to be at least of the same order as the effects of nuclear charge screening by filled electron shells.     

Electromigration and permeation of hydrogen and deuterium in silver

A steady state flow technique was used to measure the effective charge number (Z*) and permeability (N) of hydrogen and deuterium in silver. Over the range of temperature (485–720°C) and pressure (220–750 torr) the effective charge number is a constant. The interstitial impurity migrates in the direction of the electron wind with Z_H* = ?6·8 and Z_D* = ? 18. The values of Z* are of the same order as self-electromigration but the size of the isotope effect is surprising. The quantum theories used to explain the isotope effect for hydrogen electromigration in Fe and Ni appear to fail here. In order to determine the effective charge number is was necessary to measure the permeability. For both H₂ and D₂, the permeability in silver follows the equation N = N_O exp(? Q/RT) where N_0D = 2·39 ± 0·40, Q_D = 14400 ± 300, N_OH = 2·86 ± 0·70 and Q_H = 14200 ± 500. Here Q is in units of cal/mol and N is in units of cc(ntp)/(sec - atm² - cm) The isotope effect ratio N_H/N_D = 1·25 was smaller than the classically expected value of (2)^1/2, but could be explained by the theory of Ebisuzaki, Kass and O'Keeffe.     

Spin-orbit coupling constants from semi-empirical wavefunctions

The problem of computing spin-orbit coupling constants from wave-functions of a semi-empirical variety are considered specifically for SCF wavefunctions with intermediate neglect of differential overlap. The incorporation of the 1s electrons into a ‘core’ should result in an effective nuclear charge of Z′ = Z - 2·5846 being used in one-electron terms, but for agreement with experiment the results have to be reduced by some 70 per cent. This reduction factor is different for ions. If the multiplicative factor is included good agreement between observed and calculated spin-orbit coupling constants is given.