Charge Distribution Of Ions Research Articles

Recent Results from Lohengrin on Fission Yields and Related Decay Properties

The Lohengrin mass spectrometer is one of the 40 instruments built around the reactor of the Institute Laue-Langevin (France) which delivers a very intense thermal neutron flux. Usually, Lohengrin was combined with a high-resolution ionization chamber in order to obtain good nuclear charge discrimination within a mass line, yielding an accurate isotopic yield determination. Unfortunately, this experimental procedure can only be applied for fission products with a nuclear charge less than about 42, i.e. in the light fission fragment region. Since 2008, a large collaboration has started with the aim of studying various fission aspects, mainly in the heavy fragment region. For that, a new experimental setup which allows isotopic identification by γ-ray spectrometry has been developed and validated. This technique was applied on the 239Pu(nth,f) reaction where about 65 fission product yields were measured with an uncertainty that has been reduced on average by a factor of 2 compared with what was that previously available in nuclear data libraries. The same γ-ray spectrometric technique is currently being applied to the study of the 233U(nth,f) reaction. Our aim is to deduce charge and mass distributions of the fission products and to complete the experimental data that exist mainly for light fission fragments. The measurement of 41 mass yields from the 241Am(2nth,f) reaction has been also performed. In addition to these activities on fission yield measurements, various new nanosecond isomers were discovered. Their presence can be revealed from a strong deformed ionic charge distribution compared to a 'normal' Gaussian shape. Finally, a new neutron long-counter detector designed to have a detection efficiency independent of the detected neutron energy has been built. Combining this neutron device with a Germanium detector and a beta-ray detector array allowed us to measure the beta-delayed neutron emission probability Pn of some important fission products for reactor applications.

Crystal orientation dependence of charge distributions of He ions scattered from rutile TiO2(1 1 0) surfaces

It is well known that the charge distributions of medium energy He ions scattered from solid surfaces depend on emerging energy and angle as well as surface materials. We analyzed emerging energy and angle dependence of He+ fractions for medium energy He ions scattered from top-layer Ti atoms at the [11¯0]- and [001]-azimuth of rutile TiO2(110). He+ fractions for the [001]- and [11¯0]-azimuth were equilibrated at emerging angles (scaled from surface normal) above ∼75° and ∼85°, respectively. It was also found that non-equilibrated He+ fractions observed at smaller emerging angles for the [11¯0]-azimuth were larger more than 20% than those for the [001]-azimuth and the difference between the He+ fractions for the [11¯0]- and [001]-azimuth increased with increasing emerging energy. The Ti–Ti bond length along the [11¯0]-axis is more than twice that along the [001]-axis. Thus the He ions scattered from top-layer Ti atoms at the [001]-azimuth interact with many outer electrons of the aligned top-layer Ti atoms until leaving from surfaces. A He ion immediately after a large-angle collision has no bound electron because of time–energy uncertainty. The He2+ ion then undergoes electron capture and loss processes during passing through the surface. In this regard, the non-equilibrated He+ fractions for the [001]-azimuth are smaller than those for the [11¯0]-azimuth.

Effect of density on the equilibrium charge distribution of carbon and oxygen ions

Theoretical estimation of the equilibrium charge distribution of carbon and oxygen ions passed through a matter is obtained. The coefficient considering the effect of density on the charge distribution of these ions is calculated for an amorphous medium consisting of atoms with the nuclear charge Z t (Z t ≤ 54). An oscillating dependence of the average ion charge on the nuclear charge of the target atom is obtained which cannot be described by empirical relations.

Methods of estimation of equilibrium charge distribution of ions in solid and gaseous media

Abstract The new version of theoretical estimation of equilibrium charge distribution of ions passing through the matter is proposed. This estimation is based on the correction of charge exchange cross sections for gases taking into account the density effect. The results of calculations are compared with experimental data and with empirical estimation based on the averaging of experimental data for charge distributions of ions in gases and solids. The theoretical method describes the experimental oscillations of width of the charge distribution in contrast to the empirical method.

The calculation of electron chemical potential and ion charge state and their influence on plasma conductivity in electrical explosion of metal wire

The electron chemical potential and ion charge state (average ion charge and ion distribution) are important parameters in calculating plasma conductivity in electrical explosion of metal wire. In this paper, the calculating method of electron chemical potential and ion charge state is discussed at first. For the calculation of electron chemical potential, the ideal free electron gas model and Thomas-Fermi model are compared and analyzed in terms of the coupling constant of plasma. The Thomas-Fermi ionization model, which is used to calculate ion charge state, is compared with the method based on Saha equation. Furthermore, the influence of electron degenerated energy levels and ion excited states in Saha equation on the ion charge state is also analyzed. Then the influence of different calculating methods of electron chemical potential and ion charge state on plasma conductivity is discussed by applying them in the Lee-More conductivity model.

Maxwell stress-induced flow control of a free surface electro-osmotic flow in a rectangular microchannel

Multiphase flow control is a challenging task in microfluidic systems. Application of such ideas in electro-osmotic actuation of multiphase flows, which involves a complex convolution of phenomena ranging from electro-chemistry to hydrodynamics, is even more tricky. Most of the existing studies in the field have limited their scope to the thin electric double layer (EDL) limit, where the role of ionic space charge distribution in the EDL is simplified to provide a slip velocity boundary condition at the substrate, and the role of the fluid–fluid interface is limited to continuity of velocity and hydrodynamic shear stress. In this study, electro-osmotic flow of two immiscible fluids, an electrolytic solution and an inert gas, are studied in a rectangular microchannel and the role of interfacial potential and Maxwell stress-generated dynamics is explored in a wide range of EDL thicknesses. A net stress term is used in the transport equations which includes the electric effects by Maxwell stress as well as the hydrodynamic stress. It is observed that the free surface, depending upon its potential may enhance the fluid velocity or act as a rigid wall. With the help of two-dimensional velocity contour plots, the role of various flow parameters on flow profile is discussed. Further, a parametric analysis of flow rate gives interesting insights into the flow rate reversal and control in such microfluidic devices.

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the eff ects of polarizable drift gases and ionic charge distribution

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the eff ects of polarizable drift gases and ionic charge distribution

Charge distribution and mobility of lithium ions in Li2TiO3 from 6,7Li NMR data

A comparative analysis of 6,7Li NMR spectra is performed for the samples of monoclinic lithium titanate obtained at different synthesis temperatures. In the 7Li NMR spectra three lines are found, which differ in quadrupole splitting frequencies vQ and according to ab initio EFG calculations are assigned to three crystallographic sites of lithium: Li1 (vQ ∼ 27 kHz); Li2 (vQ ∼ 59 kHz); Li3 (vQ ∼ 6 kHz). The dynamics of lithium ions is studied in a wide temperature range from 300 K to 900 K. It is found that the narrowing of 7Li NMR spectra as a result of thermally activated diffusion of lithium ions in the low-temperature Li2TiO3 sample is observed at a higher temperature in comparison with a sample of high-temperature lithium titanate. Based on the analysis of 6Li NMR spectra it is assumed that there is mixed occupancy of lithium and titanium sites in the corresponding layers of the crystal structure of low-temperature lithium titanate, which hinders lithium ion transfer over regular crystallographic sites.

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the effects of polarizable drift gases and ionic charge distribution

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM-MS) using drift-gases with varying masses and polarizabilities. Despite the reduced length of the cell (18 cm), a pair of constitutional isomers, N-butylaniline and para-butylaniline, with theoretical collision cross-section values in helium (ΩHe ) differing by as little as 1.2 Å(2) (1.5%) but possessing contrasting charge distribution, showed baseline peak-to-peak resolution (Rp-p ) for their protonated molecules, using carbon dioxide (CO2), nitrous oxide (N2O) and ethene (C2H4 ) as the TWIM drift-gas. Near baseline Rp-p was also obtained in CO2 for a group of protonated haloanilines (para-chloroaniline, para-bromoaniline and para-iodoaniline) which display contrasting masses and theoretical ΩHe , which differ by as much as 15.7 Å(2) (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans-oleic acid and cis-oleic acid possessing nearly identical theoretical ΩHe and ΩN2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift-times were observed for the 1,3-dialkylimidazolium ions when comparing He, N2 and N2O. Using density functional theory as a means of examining the ions electronic structure, and He and N2-based trajectory method algorithm, we discuss the effect of the long-range charge induced dipole attractive and short-range Van der Waals forces involved in the TWIM separation in drift-gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift-gases could improve separation and the overall success of TWIM-MS analysis.

Charge distribution of ions in low-current vacuum-arc plasma

The charge distribution of vacuum-arc ions has been investigated for the arc between copper electrodes at currents varied from 8 to 60 A (with the arc voltage increased from 21 to 24 V). Plasma contains copper ions with charge states from +1 to +4. The mean ion charge state increases from 2.15 to 2.24 (i.e., by only 4%) due to a small increase in the fractions of multiply charged ions (Cu2+ and Cu3+) in the total ion flux. This conclusion does not contradict that of the ecton model of vacuum-arc cathode spot, according to which the number of cells in the spot that are due to microexplosions on the cathode increases proportionally to the arc current.

IPEC Solver: Numerical simulation tool to study inter-polyelectrolyte complexation

IPEC Solver is a Windows program designed to analyze the stability of core–shell inter-polyelectrolyte complexes formed by complexation of oppositely charged block copolymers. The two-dimensional size distribution of the complexes composed by different numbers of positively or negatively charged polyelectrolytes is calculated based on the scaling model of block copolymer aggregation and Poisson–Boltzmann theory for electrostatic interactions [V.A. Baulin, E. Trizac, Self-assembly of spherical inter-polyelectrolyte complexes from oppositely charged polymers, Soft Matter 8 (25) (2012) 6755–6766]. Salt effects, charge distribution and distributions of labile cations and anions around the complexes are calculated numerically as a function of chain composition and solvent properties. Program summaryProgram title: IPEC SolverCatalogue identifier: AEPM_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPM_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 53802No. of bytes in distributed program, including test data, etc.: 4582576Distribution format: tar.gzProgramming language: C++ (VS.10)Computer: PCOperating system: WinXP, Win7Has the code been vectorized or parallelized?: Supports parallel computation through OpenMPRAM: 1 GBClassification: 16.11Nature of problem:This free software is designed to illustrate physical mechanisms of self-assembly of inter-polyelectrolyte complexes in the presence of salt. It can suggest an optimal structure of the aggregates as a function of the structure of block copolymers.Solution method:The distribution of the complexes composed by a different number of positively or negatively charged polyelectrolytes is calculated based on a scaling model of block copolymer aggregation and Poisson–Boltzmann theory for electrostatic interactions [V.A. Baulin, E. Trizac, Self-assembly of spherical inter-polyelectrolyte complexes from oppositely charged polymers, Soft Matter, 8 (25) (2012) 6755–6766]. Salt effects, charge distribution and distributions of labile ions around the complexes are provided.Restrictions:IPEC complex is assumed to have a core–shell structure: a spherical core containing charged polymers is surrounded by a neutral corona. To insure stability of the solution, salt concentration, ka>0.2Additional comments:Solves the Poisson–Boltzmann equation in a broad range of parameters.Running time:From seconds to several hours.

Charge-state distributions of fast diatomic carbon ions and dissociated fragments passing through microcapillaries

We measured charge distributions of fast diatomic molecular ions after transmission through microcapillaries. Projectile beams of C2 ions with velocities of 0.89–1.79 au were incident on single-tapered capillaries with two different outlet diameters of 7.7 and 13.7 µm. We found that most of the transmitted primary C2 ions retain their incident charge states. For dissociated C1 fragments resulting from scattering with capillary-wall surfaces, their average charges increase with increasing velocity. The velocity dependence exhibits a similar trend to that of the equilibrium charge of atomic carbon particles that penetrate through matter. It was concluded that the molecular fragmentation during the transmission occurs mainly via grazing scattering at shallow layers below the surface of capillaries.

Width of the equilibrium charge distribution of heavy ions in solid and gaseous media

Based on an analysis of the experimental data on the charge distributions of ions in gases and solids, the analytical parameterization of the width of the charge distribution as a function of the energy, the average equilibrium ion charge, ion nuclear charge, and nuclear charge of target atom has been obtained. The proposed relations are applicable in a broad energy range and describe the existing experimental data satisfactorily.

Charge distribution of nitrogen ions reflected from copper and graphite surfaces

A method for the theoretical estimation of the equilibrium charge distribution of ions passed through a media is proposed. It is based on the correction of charge-exchange cross sections for gases using a factor taking the density effect into account. The calculated charge distribution of N ions in graphite agrees well with the existing experimental data. This method makes it possible to estimate the charge distribution of fast N ions reflected from a Cu surface.

Empirical estimation of the equilibrium charge distribution of heavy ions in solid and gaseous media

Abstract Based on the analysis of experimental data on equilibrium charge distributions of ions in gases and solid media, the analytical parameterization of the charge distribution width as a function of the average ion charge and nuclear charges of the ion and the target atom and that of the asymmetry as a function of the average ion charge are obtained. The proposed relations are applicable in a broad energy interval and describe the existing experimental data satisfactorily.

Molecular Dynamics Simulation of the Effects of NaCl on Electrostatic Properties of Newton Black Films

The effects of NaCl on electrostatic properties of Newton black films (NBF) coated with two monolayers of sodium dodecyl sulfate were investigated by using molecular dynamics simulations. Film systems without salt and with 1.0 mol/L NaCl were studied separately. Charge density profiles of salt ions are calculated and fitted using a function we proposed. Fitting results show that adding NaCl leads to more positive charge adsorbed to the surface and less diffusing in the middle of the film. More positive charge adsorbed to the surface leads to the destruction of solvation shells around amphiphilic groups, so that water molecules arrange less regularly. Adding NaCl leads to a decrease of both ions and water contributions to the electrostatic field, which are controlled by ionic charge distributions and water orientations. The relative decrements of ions and water contributions determine the difference in electrostatic potential. On the basis of the investigation of electrostatic potential and species distrib...

Polarization of a Diffuse Soft Particle Subjected to an Alternating Current Field

The polarization of a diffuse soft particle submerged in an aqueous electrolyte and subjected to a uniform alternating electric field is theoretically analyzed with the standard electrokinetic model (the Poisson-Nernst-Planck equations). The particle consists of a rigid uncharged core and a charged diffuse polyelectrolytic shell (soft layer) permeable to ions and solvent. Our focus is on the impact of the characteristics of the soft layer including the Donnan potential, the soft layer thickness, and the friction coefficient of the soft layer on the dipole coefficient, characterizing the strength of the polarization. Under the limits of thin double layers and thin polyelectrolytic shells, approximate analytical expressions to evaluate the dipole moment coefficients are derived for high-frequency and low-frequency ranges, respectively. The analytical results are compared and agree favorably with those numerically computed by the standard model. Interestingly, we discover that when the double layer is comparable to the soft layer the dipole moment behaves qualitatively differently at different Donnan potentials. When the Donnan potential is small, the dipole moment decreases as the double layer increases. In contrast, at large Donnan potentials, the dipole moment increases with the increase in the double layer. The distinct responses to Donnan potentials are attributed to the impact of the associated double layer on the charge distribution of mobile ions inside the soft layer. The theoretical model provides a fundamental basis for interpreting the polarization of heterogeneous systems, including environmental or biological colloids or microgel particles.

Bovine β-Lactoglobulin Is Dimeric Under Imitative Physiological Conditions: Dissociation Equilibrium and Rate Constants over the pH Range of 2.5–7.5

The oligomerization of β-lactoglobulin (βLg) has been studied extensively, but with somewhat contradictory results. Using analytical ultracentrifugation in both sedimentation equilibrium and sedimentation velocity modes, we studied the oligomerization of βLg variants A and B over a pH range of 2.5–7.5 in 100 mM NaCl at 25°C. For the first time, to our knowledge, we were able to estimate rate constants (koff) for βLg dimer dissociation. At pH 2.5 koff is low (0.008 and 0.009 s−1), but at higher pH (6.5 and 7.5) koff is considerably greater (>0.1 s−1). We analyzed the sedimentation velocity data using the van Holde-Weischet method, and the results were consistent with a monomer-dimer reversible self-association at pH 2.5, 3.5, 6.5, and 7.5. Dimer dissociation constants KD2-1 fell close to or within the protein concentration range of ∼5 to ∼45 μM, and at ∼45 μM the dimer predominated. No species larger than the dimer could be detected. The KD2-1 increased as |pH-pI| increased, indicating that the hydrophobic effect is the major factor stabilizing the dimer, and suggesting that, especially at low pH, electrostatic repulsion destabilizes the dimer. Therefore, through Poisson-Boltzmann calculations, we determined the electrostatic dimerization energy and the ionic charge distribution as a function of ionic strength at pH above (pH 7.5) and below (pH 2.5) the isoelectric point (pI∼5.3). We propose a mechanism for dimer stabilization whereby the added ionic species screen and neutralize charges in the vicinity of the dimer interface. The electrostatic forces of the ion cloud surrounding βLg play a key role in the thermodynamics and kinetics of dimer association/dissociation.

Attosecond Plasma Wave Dynamics in Laser-Driven Cluster Nanoplasmas

We introduce a microscopic particle-in-cell approach that allows bridging the microscopic and macroscopic realms of laser-driven plasma physics. As a first application, resonantly driven cluster nanoplasmas are investigated. Our analysis reveals an attosecond plasma-wave dynamics in clusters with radii R is approximately equal to 30 nm. The plasma waves are excited by electrons recolliding with the cluster surface and travel toward the center, where they collide and break. In this process, energetic electron hot spots are generated along with highly localized attosecond electric field fluctuations, whose intensity exceeds the driving laser by more than 2 orders of magnitude. The ionization enhancement resulting from both effects generates a strongly nonuniform ion charge distribution. The observed nonlinear plasma-wave phenomena have a profound effect on the ionization dynamics of nanoparticles and offer a route to extreme nanoplasmonic field enhancements.

Energy and charge distribution of helium atoms reflected from a Cu surface under grazing incidence

The energy and charge distributions of helium ions and atoms reflected from a Cu surface at grazing incidence have been measured at the energies 250 and 300 keV. The dependence of the relative number of helium atoms in the scattered beam on the scattering angle at incidence angles less than 2° and scattered particle energies below 150 keV has been discovered. It is shown that, for a theoretical estimation of the charge fractions of particles reflected from the target surface, charge-exchange cross sections used in calculations must be corrected when solids are considered instead of gases.