Kinetic Ejection Research Articles

KINETIC ENERGY EJECTION FRACTION: A BETTER MARKER OF CARDIAC FUNCTION IN THE SINGLE VENTRICLE CIRCULATION

Ventricular volumetric ejection fraction (VV EF) is often normal in those with single ventricle circulations. This is not in keeping with their symptoms and prognosis. We propose a new simple measure of ventricular function based on kinetic energy, the kinetic energy ejection fraction (KE EF), and

Assessing cardiac function in the single ventricle circulation: Kinetic energy ejection fraction

Background Those with single ventricle circulations often have a normal ventricular volumetric ejection fraction (VV EF) which is not in keeping with their symptoms and prognosis. Recently four-dimensional flow (4Dflow) magnetic resonance imaging (MRI) has been used to extract parameters of intra-cardiac kinetic energy (KE). There has been recent interest in measuring ventricular KE in health and disease to see if this could provide an additional tool in the assessment of ventricular function. We propose a new simple measure of ventricular function based on kinetic energy, the kinetic energy ejection fraction (KE EF), and assess its usefulness in patients with single ventricle circulation.

Electron ejection by He+ ion impact at rare-gas films: Energy- and spin-resolved studies

The electron ejection processes operative when He+ ions with energies in the range 10–500eV impact adsorbed rare-gas layers are examined both by analyzing the energy distribution of electrons ejected from the surface and by use of spin-labeling techniques, specifically the use of electron-spin-polarized He+ ions coupled with measurement of the ejected electron polarization. The data for xenon films indicate that at low ion energies electron ejection is associated primarily with an Auger neutralization process similar to that seen at clean high-work-function metal surfaces. At the higher ion energies, however, kinetic ejection becomes important and provides an increasing contribution to the total electron yield. For krypton films kinetic ejection is the dominant ejection mechanism although a small signal associated with Auger neutralization is also seen. In the case of argon only kinetic ejection occurs.

The dynamics of He + ion neutralization at a xenon film: Energy- and spin-resolved studies

The neutralization of He + ions with energies in the range 10–500 eV at an adsorbed xenon layer is examined both by analyzing the energy distribution of electrons ejected from the surface and by use of spin-labeling techniques, specifically the use of electron-spin-polarized He + ions coupled with measurement of the ejected electron polarization. The data indicate that neutralization proceeds via an Auger process similar to that which occurs at a clean high-work-function metal surface. At the higher ion energies, however, kinetic ejection becomes important and provides an increasing contribution to the total electron yield.

High-efficiency target ion sources for radioactive ion beam generation

In this report, high-temperature ion sources are described, which have demonstrated the high ionization efficiency, species versatility, and operational reliability required at isotope-separator-online (ISOL) based radioactive ion beam facilities such as the Holifield Radioactive Ion Beam Facility (HRIBF). Specific attention is given to the ion optics, operational parameters, thermal transport properties, emittances, and ionization efficiencies of the HRIBF ion sources that have been carefully designed for safe handling in the high-level radiation fields incumbent at such facilities. Included in the article are descriptions and performance data for high-temperature, positive- (electron impact and surface ionization) and negative- (kinetic ejection and surface ionization) ion sources as well as low-temperature, batch-mode negative-ion sources, developed for processing long-lived isotopes that have been the principal contributors to recent successes held at the Holifield Radioactive Ion Beam Facility.

Efficient negative-ion sources for radioactive ion beam applications (abstract)

Direct extraction, negative-surface ionization, and sputter-type sources have been designed to efficiently ionize specific members of the group VII A elements (F, Cl, Br, I, and At) for use in the nuclear structure physics and nuclear astrophysics research programs at the Holifield Radioactive Ion Beam Facility (HRIBF). A negative surface ionization source that utilizes a solid, spherical geometry, LaB6 ionizer (φ≅2.7 eV) for negatively ionizing Cl, Br, l, and At. During off-line evaluation, the ionization efficiency for Cl− generation ranged between 15% and 20% and for Br− generation, between 15% and 25%. Chemically active elements, such as fluorine, are often released from refractory host materials in a variety of molecular forms. Consequently, the LaB6 surface ionization source, described above, is ineffective for simultaneously dissociating and negatively ionizing this element. To overcome this problem, a new concept source, referred to as the kinetic ejection negative ion source (KENIS), was developed. The source utilizes the Cs-sputter technique to effectively dissociate molecular carriers and ionize F at efficiencies in excess of 7%. The source has been used on-line to inject >3×107 17F−/s into the tandem accelerator and deliver ∼3×106 17F9+/s (fully stripped) to the research station for completion of important nuclear-astrophysics experiments. In this article, emphasis will be placed on the design details, materials of construction, ion optics, operational parameters, thermal transport properties, emittances, and measured ionization efficiencies for these sources.

The development of the 17F beam at the Holifield radioactive ion beam facility

This report details some of the key technological developments employed at the Holifield Radioactive Ion Beam Facility (HRIBF) to produce beams of 17F using the 16O(d, n) 17F reaction. The oxide fiber target material used at the HRIBF is described and a comparison is made between the 17F yield achieved using light (Al) and heavy (Hf) metal oxide fibers. The development of the Kinetic Ejection Negative Ion Source (KENIS) employed in this work is also discussed along with the operational principles of the source. Finally, a detailed description of the HfO 2 target configuration used to produce 10 7–10 8 17F ions/s for over 850 hours of operation is provided. To date, seven nuclear physics experiments using accelerated beams of 17F and 18F produced using this apparatus have been performed over an energy range of 10–170 MeV.

鉄系粉末金型潤滑成形法の最適化と抜出し挙動の動的および静的摩擦解析

The present paper describes a new evaluation for ejection behavior in iron powder compacting process and optimum die-wall lubrication conditions. In the new method, ejection force is broken down to static friction force and kinetic friction force, which make it possible to explain ejection behavior more clearly. The incremental rate of kinetic ejection force is more important for surface quality of compacts than the value of static ejection force. Among three lubricants used, zinc stearate showed the highest static ejection force but the lowest incremental rate of kinetic ejection force. It also showed an excellent surface quality of the compacts. Characteristic crystalline structure gave a low shear strength, which contributed to decrease the kinetic friction. In the die-wall lubrication method, the projected area rate of lubricant particles should be 90% or more, therefore, the multiple coating method which is repetition of short time shot is requested.

Model for the chemical erosion of graphite due to low-energy H+ and D+ impact

A methane erosion yield model has been developed using the principal atomistic reactions outlined by Küppers and co-workers [eg., A. Horn, A. Schenk, J. Biener, B. Winter, C. Lutterloh, M. Wittmann, and J. Küppers, Chem. Phys. Lett. 231, 193 (1994)] with additional terms to account for the energy of the incident particles, namely, kinetic ejection and damage deposition. Furthermore, modifications were made to the previous models by using distributed activation energies for methyl and hydrogen release as well as an activated Eley-Rideal abstraction process. Fitting of this model to experimentally measured methane yield data shows excellent agreement, except for low energy (⩽25 eV) impact at temperatures above ∼800 K. We have provided a sound physical basis for the behavior of the free fitting parameters and conclude that most of the processes associated with low-energy impact on pyrolytic graphite leading to methane production have been incorporated. Possible extensions of the model to include heavy hydrocarbons and total chemical erosion yields are also discussed. Due to the lack of comprehensive experimental data on the flux dependence of hydrocarbon erosion, the flux dependence of the fitting parameters could not be explored and so the effect of flux density requires further modeling considerations.

Prototype negative-ion sources for radioactive ion-beam generation

Radioactive ion beams (RIBs) of F17 and F18 are of interest for investigation of astrophysical phenomena such as the “hot” CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F−, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. We have conceived and evaluated two prototype negative-ion sources for potential use for RIB generation: (1) a direct extraction source and (2) a kinetic-ejection source. Both sources utilize Cs vapor to enhance F− formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F−, and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency η for formation and extraction of F− for the direct extraction negative-ion source is found to be η∼1.0% while the characteristic delay time τ for transport of F and fluorides through the source is, typically, η∼120 s; the analogous efficiencies and delay times for the kinetic ejection negative-ion source are, respectively: η=∼3.2% and τ=∼70 s.

Prototype negative ion sources for radioactive ion beam generation (abstract)

Radioactive ion beams (RIBs) of F17 and F18 are of interest for investigation of astrophysical phenomena such as the “hot” CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F−, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. We have conceived and evaluated two prototype negative ion sources for potential use for RIB generation: a direct extraction source and a kinetic ejection source. Both sources utilize Cs vapor to enhance F− formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F− and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency η for formation and extraction of F− for the direct extraction negative ion source is found to be η∼1.0%, while the characteristic delay time τ for transport of F and fluorides through the source is typically, η∼120 s; the analogous efficiencies and delay times for the kinetic ejection negative ion source are, respectively: η=∼3.2% and τ=∼70 s.

Analytic description of the chemical erosion of graphite by hydrogen ions

One main concern about the use of graphite as a plasma facing material is the enhanced erosion under hydrogen bombardment due to hydrocarbon formation. In view of the lifetime evaluation of plasma exposed carbon components and of impurity production in present and future machines such as ITER, an analytical expression for the erosion yield by chemical sputtering for the relevant energies, temperatures and incident fluxes is of special importance. An extrapolation to fluxes and energies relevant for high density divertor plasmas has not been possible up to now on the basis of semiempirical fits to laboratory data. Starting from a short review of the existing empirical formulas, recent detailed investigations of the atomistic processes for the thermally activated hydrocarbon emission are described, which enable the formulation of an improved analytical description including the ion flux as a parameter. The chemical erosion of graphite by hydrogen bombardment results from two processes: the thermally activated hydrocarbon emission, Ytherm, and a surface process at low energies and low temperatures resulting from the kinetic ejection of surface hydrocarbon complexes from collisional energy transfer, Ysurf. The new analytic description can be fitted well to the existing data for ion beam erosion, and extrapolation to divertor relevant fluxes is possible. At high ion fluxes the maximum of chemical erosion is shifted to higher temperatures, where annealing of damaged structures leads to a stronger reduction of Ytherm than previously estimated. There are no data on a possible flux dependence of Ysurf, leaving still some uncertainty in extrapolation

Electronically stimulated sputtering and luminescence from solid argon.

Electronic excitation of condensed-gas solids by MeV light ions results both in luminescence and in kinetic ejection of atoms and molecules from the surface of the solid. This work reveals that ejection of Ar atoms from electronically excited solid argon films arises from two nonradiative repulsive dissociation steps in the deexcitation decay sequence which contains the major radiative transition. A hole-diffusion model with nonradiative quenching at the metal substate on which the films are grown accounts for the dependence of the sputtering and luminescence on film thickness and gives an estimate of 230 A\r{} for the hole-diffusion length. The hole-diffusion model also explains the nearly linear dependence of the sputtering and luminescence yields on electronic stopping cross section for high-velocity incident ions. Intentionally added ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$ impurities reduce the hole-diffusion length. These reductions provide values for effective reaction volumes, ${k}_{+}$${\ensuremath{\tau}}_{+}$, of 7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ ${\mathrm{cm}}^{3}$ for ${\mathrm{O}}_{2}$ and 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ ${\mathrm{cm}}^{3}$ for ${\mathrm{N}}_{2}$, where ${k}_{+}$ is the interaction rate constant of the holes with the impurity and ${\ensuremath{\tau}}_{+}$ is the lifetime of holes in pure films. The ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$ impurities also quench nonmobile luminescent excimers, ${\mathrm{Ar}}_{2}^{\mathrm{*}}$, over large distances: 21 A\r{} for ${\mathrm{O}}_{2}$ and 11 A\r{} for ${\mathrm{N}}_{2}$. The magnitude of the sputtering yield characterizes the vacuum interface as primarily hole reflecting, but with a surface-hole-trapping rate about 6 times that of the bulk. Surface ${\mathrm{O}}_{2}$ impurity greatly enhances surface trapping of free holes. Sputtering of ${\mathrm{Ar}}_{2}^{\mathrm{*}}$ dimers is evident from the observation of 11.3-eV luminescence in the region in front of the argon films. The dimers are emitted with \ensuremath{\sim}0.8 eV of kinetic energy. This is consistent with the repulsive decay forming an energetic ${\mathrm{Ar}}^{\mathrm{*}}$, which forms ${\mathrm{Ar}}_{2}^{\mathrm{*}}$ upon exiting or, possibly, the ejection of an ${\mathrm{Ar}}_{2}^{\mathrm{*}}$ during trapping at the surface.

Detection of low energy neutrals by a channel electron multiplier

A method for determining relative channel electron multiplier (CEM) detection efficiencies for low energy neutrals using the technique of direct recoiling is described. The method uses time-of-flight analysis of low-energy atoms recoiling from an energetic ion/surface collision. The system used for demonstration is 1–10 keV Ne + scattering from a polyimide resin surface, producing H and C recoils. The behavior of the CEM detection efficiency γ can be divided into two regions: A flat plateau region is observed at high velocity while below a specific velocity, ν H = 4.4 × 10 7 and ν C = 3.2 × 10 7 cm/s, γ decreases linearly with velocity with slope dγ dν = 6.4 × 10 −8 s/cm . This behavior is discussed in terms of secondary electron emission by a kinetic ejection process.

Kinetic ejection of electrons from oxidized AgMg (98.5% Ag) dynode of an EMI 9603B particle multiplier by the impact of K+ ions

Kinetic ejection of electrons from oxidized AgMg (98.5% Ag) dynode of an EMI 9603B particle multiplier by the impact of K+ ions

Kinetic electron ejection by scattered neutralized positive ions

A crude energy analysis of positive secondary currents (measured on the collecting surfaces) from clean single-crystal targets of tungsten, molybdenum and vanadium, as well as polycrystalline tungsten, indicates that significant proportions of the currents measured result not only from sputtered target ions but also from kinetic electron ejection from the collecting surfaces by scattered incident particles. Some correlation has been achieved with kinetic ejection thresholds calculated according to simple hard-shape collision theory.

Secondary electron emission from Au, Mo, and CuBe by high-charge-number laser-produced metal ions

The secondary electron emission coefficient γ for gas-covered Au, Mo, and CuBe surfaces was determined in the energy range 0.3–22.4 keV for incident ions as follows: H+, C+ 1 → 6, Al+ 1 → 10, Cu+ 1 → 9, Ta+ 1 → 3. Energetic highly charged ions produced by a Nd laser beam focused on solid targets in vacuum were allowed to impinge on a metal target. The electrons ejected were collected and the current measured. Potential ejection is dominant over kinetic ejection in this energy range. The Parilis-Kishinevskii theory of secondary electron emission, based primarily on ionization of metal target atoms with subsequent recombination through an internal Auger process, and the present experimental results for low charge numbers (n ≤ 3e) and high mass (A ≥ 27) are only in qualitative agreement. For high charge numbers (n ≥ 4e) or low mass (A ≤ 12), there is no agreement.

Secondary Electron Emission from Insulators by Ion Bombardment

The characteristics of secondary electron emission from a glass surface by Ar/sup +/ ions were investigated experimertally. The yields from glass and quartz microsheets were larger than those from stainless steel. It was first observed that field-enhanced emission and seif-sustained emission were caused by the surface charge. Because increasing of the yield has technological demand, HF etching and sandblast were attempted as one of the means of increasing yield. Then the yields of etched and sandblasted samples were about two times larger than that of nonetched or nonsandblasted sample. Field-enhanced emission and seif-sustained emission cannot be irterpreted only with kinetic ejection or potertial emission theory. A simple model is proposed in which the work function decreases by the band bending with the accumulation of positive charge near the surface. (auth)

Model for Kinetic Electron Ejection from Gas-Covered Surfaces

A model for the ionization of molecules adsorbed to a surface by energetic ion bombardment is described. The transition of a hypothetical "average" ion to the surface through a low-density surface gas is analyzed and assumed to represent the ensemble of collision processes encountered in the real case. This leads to the determination of the probability of freeing an electron from an atom in the surface gas by an impinging ion. For surfaces with a monolayer or more of adsorbate, the probability is comparable in size to coefficients of potential and kinetic ejection for ion kinetic energies above 1000 eV.

EXCITATION OF ELECTRONS IN SOLIDS BY RELATIVELY SLOW ATOMIC PARTICLES

I. Introduction 332 II. Excitation of Electrons Due to the Internal Energy of the Atomic Particle-plus-solid System and Potential Ejection of Electrons 332 III. Kinetic Ejection of Electrons in Vacuum 342 IV. Radiative (Induced) Conductivity of Semiconductors Bombarded with Ions 353 V. Excitation of Luminescence by Ion Bombardment of Solids, and Ionoluminescence 358 VI. Conclusion 362 Cited Literature 364