Showing papers on "Charged particle published in 1998"

Method and apparatus for directing ions and other charged particles generated at near atmospheric pressures into a region under vacuum

Abstract: A method and apparatus for focusing dispersed charged particles. More specifically, a series of elements within a region maintained at a pressure between 10 -1 millibar and 1 bar, each having successively larger apertures forming an ion funnel, wherein RF voltages are applied to the elements so that the RF voltage on any element has phase, amplitude and frequency necessary to define a confinement zone for charged particles of appropriate charge and mass in the interior of the ion funnel, wherein the confinement zone has an acceptance region and an emmitance region and where the acceptance region area is larger than the emmitance region area.

The framework of plasma physics

Abstract: Foreword by David Pines The Nature of Plasma Charged Particle Motion Fluid Description of a Plasma The Cold Plasma Model and Waves MHD and the Drift Model Vlasov Description of a Plasma Binary Collisions Collisional Transport Turbulent Transport.

Phenomenology of Massive Vectorlike Doublet Leptons

Abstract: Massive vectorlike electroweak doublets are generic in many extensions of the standard model. Even though one member of the doublet is necessarily electrically charged these particles are not easily detected in collider experiments. The neutral and charged states within the doublet are split by electroweak symmetry breaking. In the absence of mixing with other states, the radiatively generated splitting is in the range 200{endash}350 MeV for m{approx_gt} (1) /(2) thinspm{sub Z} . The charged state decays to the neutral one with an O()>cm decay length, predominantly by emission of a soft charged pion. The best possibility to detect these massive charged particles is to trigger on hard initial state radiation and search for two associated soft charged pions with displaced vertices. The mass reach for this process at LEPII is limited by luminosity rather than kinematics. {copyright} {ital 1998} {ital The American Physical Society}

Deposition of charged particles on lung airways.

Abstract: The effect of a single electric charge on the efficiency with which ultrafine particles deposit in human airways has been investigated. When inhaled short-lived radon progeny are attached to electrically neutral particles their deposition efficiency is controlled by diffusion. But most ambient particles carry one, or a few, charges. We measured and compared the deposition (DE) of singly charged, charge-neutralized, and zero-charge 20-nm and 125-nm particles in hollow-cast models of human airways. These particle sizes were selected because they are about where modal peaks occur for the activity of the short-lived radon progeny in indoor air. For singly charged 20-nm particles deposition (+/- standard error) in the casts was 3.4 +/- 0.3 times that for charge neutralized aerosols and 5.3 +/- 0.3 times the amount deposited for zero-charged particles. Corresponding ratios for the 125-nm particles were 2.3 +/- 0.3 and 6.2 +/- 0.7. Since most ambient particles are charged this effect must be considered when models are used to predict dose from inhaled ultrafine particles.

Electronic method for controlling charged particles to obtain optimum electrokinetic behavior

Abstract: An electronic method is described whereby the applied electromotive force optimizes the electrokinetic behavior of charged particles to match closely the natural electrical response and physical structure of the system The method shapes the electromotive force's amplitude and frequency to normalize the relative interactions between the charged particles and the physical structure An injection means (1) allows this method to be applied to a broad base of physical, biological, and electrochemical processes that depend on the electrokinetic behavior of charged particles The method can effectively utilize the reactive energy or amplification occurring at natural system resonance to enhance the performance of the system without an increase in the applied power In an electrochemical process the method provides an optimized mass transport perturbation, including the electrical double layer, that is perpendicular to the electrodes Further, a battery module (52) is disclosed using this method to control and improve performance in electrolytic, galvanic, and storage modes of operation Advantages of this method include less energy consumption, better material utilization, tighter process control, simpler circuitry, lower cost, longer operational life, and higher process throughput

Diffusional Deposition of Charged Latex Particles on Water−Solid Interfaces at Low Ionic Strength

Abstract: The deposition of positively charged latex particles with radii between 20 and 100 nm on a negatively charged mica surface is investigated with atomic force microscopy at low ionic strengths. The polystyrene latex spheres with amidine headgroups are characterized as to their size distribution, electrophoretic mobility, and aggregation behavior. Surface coverage measurements take into account the polydispersity of the particles on the surface. Deposition kinetics from a quiescent solution are, for low coverage, in good agreement with diffusion-limited adsorption. At long times, the surface coverage tends toward a maximum surface coverage θmax independent of the particle concentration but depending on ionic strength. This work extends the available data for θmax for small particle size and very low ionic strengths. The values for θmax decrease with decreasing ionic strength; this trend is described with a simple model based on random sequential adsorption and the effect of overlapping double layers. Particl...

Charged particle irradiation apparatus and an operating method thereof

Abstract: A charged particle irradiation apparatus, which is capable of decreasing a lateral dose falloff at boundaries of irradiation field of charged particle beam, and reducing the size of the charged particle irradiation apparatus, is provided by controlling magnetic fields of quadrupole electromagnets 1-5 and deflection electromagnets 6-8 so that center of the charged particle beam passes always center of a scatterer irrespective of direction and intensity of a magnetic field generated by scanning electromagnets 50, 60.

Particle Charge Distribution Measurement for Commonly Generated Laboratory Aerosols

Abstract: An improved particle charge analyzer system has been developed to measure the absolute charge distribution of common generated laboratory aerosols. The charge analyzer system consists of an integral cylindrical mobility analyzer used in conjunction with an optical aerosol spectrometer, with computer assisted operation and data reduction. The charge analyzer collects aerosol particles over an absolute electrical mobility range from 4.2*10−4 to 400 cm2/(stat · Volt second) and flow rates that can vary from 0.3 to 30 liters per minute. The charge analyzer has been used to investigate the nature of spray and contact electrification during aerosol generation by measuring the residual charge distribution on the liquid and solid generated particles. In addition, the neutralization of charged particles by bipolar ions also was studied using conventional neutralizers that use ionizing radiation from alpha and beta sources. Charge distribution measurements were performed on alumina dust (Al), Arizona road ...

Photo-double-ionization of He: Fully differential and absolute electronic and ionic momentum distributions

Abstract: We measure fully differential cross sections for photo-double-ionization of helium at energies 1, 6, and 20 eV above threshold. The data have been obtained by measuring in coincidence the momentum vector of the He{sup 2+} ion and one of the electrons. Using time-of-flight and imaging techniques, we cover a solid angle of 25{endash}100{percent} 4{pi} of the final-state continuum of all particles. Therefore the experiment is not confined to any particular set of angles or energy sharing, and allows for a reliable absolute calibration. We present momentum distributions of the ions and a comprehensive set of differential cross sections for electron emission. The latter are {ital on an absolute scale} and cover both equal and unequal energy sharing{emdash}for both the fast and the slow electron fixed{emdash}and a wide range of polar angles. We also present the first data for noncoplanar geometry. For all energies the cross section is sharply peaked around the coplanar emission, i.e., both electrons are preferentially emitted in the plane of the recoiling ion and the photon polarization direction. For most of the geometries the shape of the cross sections is well described by fourth-order Wannier theory calculations. {copyright} {ital 1998} {ital The American Physical Society}

Atomic multielectron processes

Abstract: 1. Basic Experimental Techniques.- 2. Multielectron Processes Induced by Charged Particles.- 3. Collisions Involving Negative Atomic Ions.- 4. Multiple Photoionization.- References.

Plasmon excitation by charged particles moving near a solid surface

Abstract: The interaction of fast charged particles with a semi-infinite medium is described using both quantum-mechanical and semiclassical dielectric formulations. We consider the coupling with bulk and surface excitations for arbitrary trajectories of the particle and apply the solutions to several cases of special interest. Interference effects in bulk and surface excitations for some particular trajectories are described. We analyze in detail the process of reflection-electron-energy-loss spectroscopy, obtaining results for the probabilities of multiple bulk- and surface-plasmon excitations. The calculations are compared with available experimental results, showing a good description of the angular dependence of the excitation phenomenon.

Particle channeling in a bent crystal

Abstract: The channeling of high-energy charged particles in bent crystals is being used more and more extensively for steering particle beams at accelerators, for extracting a beam or its halo from an accelerator, and for splitting the extracted beam. The use of the strong intracrystalline fields of bent crystals in high-energy physics, for example, to measure the magnetic moments of short-lived particles from the spin precession angle in a bent crystal, appears to be very promising. The results of studies on the channeling of high-energy particles in a bent crystal are reviewed. The features of channeling and quasichanneling, the ionization energy losses, and the radiation emitted by channeled particles are studied. The possibility of polarization effects for channeled particles is discussed.

Fullerene nanotubes can be used when transporting gamma-quanta, neutrons, ion beams and radiation from relativistic particles

Abstract: The nanotube system is shown to be very effective when transporting the beams of neutral and charged particles. Also, it can be used for intensive radiation of relativistic leptons which is similar to channeling radiation in crystals. Now it is possible to make nanotubes of 100–300 μm length and of 1–50 nm diameter.

Europa's surface composition and sputter‐produced ionosphere

Abstract: The efficient sputtering and decomposition of Europa's regolith by energetic charged particles produces an atmosphere representative of its surface composition. In addition to O2 and H2 from the decomposition of ice, we show that molecules representative of organics and salts will be present in ionic form at levels detectable using an ion mass spectrometer on an orbiting spacecraft. Such an instrument can also measure isotope ratios to determine surface age.

Spontaneous Breaking of Translational Invariance and Spatial Condensation in Stationary States on a Ring: I. The Neutral System

Abstract: We consider a model in which positive and negative particles with equal densities diffuse in an asymmetric, CP invariant way on a ring. The positive particles hop clockwise, the negative counter-clockwise and oppositely-charged adjacent particles may swap positions. The model depends on two parameters. Analytic calculations using quadratic algebras, inhomogeneous solutions of the mean-field equations and Monte-Carlo simulations suggest that the model has three phases. A pure phase in which one has three pinned blocks of only positive, negative particles and vacancies and in which translational invariance is broken. A mixed phase in which the current has a linear dependence on one parameter but is independent of the other one and of the density of the charged particles. In this phase one has a bump and a fluid. The bump (condensate) contains positive and negative particles only, the fluid contains charged particles and vacancies uniformly distributed. The mixed phase is separated from the disordered phase by a second-order phase-transition which has many properties of the Bose-Einstein phase-transition observed in equilibrium. Various critical exponents are found.

Comparative study of ion, x-ray and neutron emission in a low energy plasma focus

Abstract: In a low energy (2.3 kJ) Mather-type deuterium plasma focus, neutron and x-ray emission is investigated by time integrated and time resolved detectors. CR-39 nuclear track ion detectors are employed for measuring charged particle angular distribution. Correlation of charged particles with neutron and x-ray emission is also investigated. The neutron emission profile is found to be composed of two pulses, the intensity and anisotropy of which vary with the filling pressure. The charged particle flux is maximum with high fluence anisotropy for the pressure range 2.5-3.0 mbar which is also the optimum pressure for high neutron emission with low fluence anisotropy . The high neutron emission with low fluence anisotropy is attributed to the presence of trapped deuterons in an anomalous magnetic field. The relevant pressure range generates favourable conditions for plasma density and pinch filament diameter. X-ray emission is generally high at low pressure. For the pressure range of 2.5-4.0 mbar, the axial neutron detector registers a hard x-ray pulse, which may escape through a half inch thick Cu flange. These results suggest that at low pressures, the collapsing current sheath interacts with the anode end and causes intense low energy x-ray emission, but the neutron emission remains low. X-rays are dominantly Cu . In the narrow pressure regime 2.5-3.0 mbar, the current sheath forms a pinch filament leading to high neutron yield with low fluence anisotropy.

Hadronic expansion dynamics in central Pb+Pb collisions at 158 GeV per nucleon

Abstract: Two-particle correlation functions of negative hadrons over wide phase space, and transverse mass spectra of negative hadrons and deuterons near mid-rapidity have been measured in central Pb+Pb collisions at 158 GeV per nucleon by the NA49 experiment at the CERN SPS. A novel Coulomb correction procedure for the negative two-particle correlations is employed making use of the measured oppositely charged particle correlation. Within an expanding source scenario these results are used to extract the dynamic characteristics of the hadronic source, resolving the ambiguities between the temperature and transverse expansion velocity of the source, that are unavoidable when single and two particle spectra are analysed separately. The source shape, the total duration of the source expansion, the duration of particle emission, the freeze-out temperature and the longitudinal and transverse expansion velocities are deduced.

Drift wave test particle transport in reversed shear profile

Abstract: Drift wave maps, area preserving maps that describe the motion of charged particles in drift waves, are derived. The maps allow the integration of particle orbits on the long time scale needed to describe transport. Calculations using the drift wave maps show that dramatic improvement in the particle confinement, in the presence of a given level and spectrum of E×B turbulence, can occur for q(r) profiles with reversed shear. A similar reduction in the transport, i.e., one that is independent of the turbulence, is observed in the presence of an equilibrium radial electric field with shear. The transport reduction, caused by the combined effects of radial electric field shear and both monotonic and reversed shear magnetic q profiles, is also investigated.

Chemistry of Ice Induced by Bombardment with Energetic Charged Particles

Abstract: The presence of intense fluxes of charged particles impinging on the solid surfaces of planets, satellites, and rings in the Outer Solar System, produces a number of effects whose knowledge appears to be essential for understanding the evolution of these objects. This type of research is based on laboratory simulations of relevant targets (e.g. molecular solids) bombarded with charged particles under physical conditions more or less similar to the astrophysical ones. Here I review the experimental results obtained, in recent years, on physical-chemical effects induced on frozen gases (CO, CO2, CH4, H2O, etc.) and mixtures simulating ice targets in space (frosts on planets, satellites, comets, etc.). In particular I discuss the ion induced formation of new species. Some properties of the organic refractory residues left over by ion-irradiation are also presented. In the Solar System, frozen surfaces are continuously bombarded by energetic ions from solar wind and flares, planetary magnetospheres and galactic cosmic rays. Many applications of the above type of experiments have been discussed in recent years and are here reviewed. These include modifications undergone by comets and satellites in the outer Solar System.

Multifragmentation of the remnant produced in the reaction of 1A GeV gold with carbon

Abstract: A high-statistics exclusive study of the multifragmentation of 1A GeV gold on carbon has been performed. Particles with Z{le}2 show evidence of emission in a first prompt stage as well as in a second equilibrium stage whereas fragments with Z{ge}3 appear to be emitted essentially only in the second stage. Two methods for the separation of the Z{le}2 particles into the two stages are given and they are in agreement. The yields for each stage are determined as a function of the event charged particle multiplicity m. The mass, nuclear charge, excitation energy per nucleon, and temperature of the remnant left after the first stage and their fluctuations have been determined as a function of m. The expansion of the remnant to fragment freeze-out is examined. The freeze-out temperature is determined from double isotope ratios as a function of m and isentropic trajectories are obtained in the temperature-density plane. The caloric curve shows a monotonic increase with excitation energy. Some of the energy is in the form of radial flow. Overall, the results are consistent with a previous statistical analysis of the data which suggests that, over a certain range of excitation energies, multifragmentation involves a continuous phase transition. {copyright}more » {ital 1998} {ital The American Physical Society}« less

Space charge in dielectrics. Energy storage and transfer dynamics from atomistic to macroscopic scale

Abstract: The consequence of the coupling of a charged particle with a polarization field is the formation of a quasi-particle called the 'polaron'. The degree of 'localization' of such charge depends on the nature of this coupling. In this way, trapping at an atomic scale is described as resulting from the evolution of a coupling involving successively: the electronic polarization field, the infrared polarization field, and the quasi-static ionic polarization field. The internal energy stored in the surrounding medium polarized by the charge is high because the charge is so well localized. The maximum of this energy is obtained for the quasi-static polarization field; its magnitude is of the order of 5 to 10 eV per trapped charge. This work addresses the physics of aging and of the breakdown process on the basis of an unsustainable increase in local internal energy within the material, due to charge trapping-the polarization around a trapped charge increases the local energy; the relaxation of the material lattice then follows a rapid detrapping of charges from their sites, releasing the local excess site region energy into the material. Such a release executes transient virtual work on the material, producing macroscopic dielectric damage, and when critical, unstable conditions are achieved in the time domain, this is followed by electrical breakdown. This interpretation of electrical material breakdown is related to bulk breakdown as observed in thin film laminate structures (/spl sim//spl mu/m) and surface flashover as seen in large structures (/spl sim/mm to cm).

Spectral universality of strong shocks accelerating charged particles

Abstract: As a rule, the shock compression controls the spectrum of diffusively accelerated particles. We argue that this is not so if the backreaction of these particles on the shock structure is significant. We present a self-similar solution in which the accelerated particles change the flow structure near the shock so strongly that the total shock compression may become arbitrarily large. Despite this, the energy spectrum behind the shock is close to E^{-3/2} independently of anything at all.

Experimental determination of fragment excitation energies in multifragmentation events

Abstract: For 50 MeV/nucleon {sup 129}Xe+{sup nat}Sn multifragmentation events, we deduced, by means of correlation techniques, the multiplicities of the hydrogen and helium isotopes which were emitted by the hot primary excited fragments produced at the stage of the disassembly of an equilibrated hot source. We also derived the relative kinetic energy distributions between the primary clusters and the light charged particles that they evaporate. From the comparison between the secondary multiplicities observed experimentally and the multiplicities predicted by the GEMINI model, we concluded that the source breaks into primary fragments which are characterized by the same N/Z ratio as the combined system. Knowing the secondary light charged particle multiplicities and kinetic energies, we reconstructed the average charges of the hot fragments and we estimated their mean excitation energies. The fragment excitation energies are equal to 3.0 MeV/nucleon for the full range of intermediate mass fragment atomic number. This global constancy indicates that, on the average, thermodynamical equilibrium was achieved at the disassembly stage of the source. {copyright} {ital 1998} {ital The American Physical Society}