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Proceedings of the workshop on some aspects of autoionization in atoms and small molecules

Description: Do we really understand the phenomenon of autoionization in atoms sufficiently well to consider it a ''mature'' topic. Can we generalize our understanding to predict behavior in systems not yet studied. Can we extract physical understanding from the encouraging results of the ''many-body calculations''. Or must we still try to understand one atom at a time. Molecular autoionization is clearly more difficult. Not only must we content with ''vibrational autoionization'' as well as ''electronic autoionization'', but the competing process of predissociation must also be taken into account. In this molecular domain, we have many experiments and many phenomena. The extant theories only deal with some cases, and are not yet able to explain some prominent observations. A group consisting of theorists and experimentalists active in the field of autoionization assembled at Argonne National Laboratory for a two-day Workshop on May 2-3, 1985, to try to provide some consensus of our present understanding and to point out the most promising direction for progress in the near future. Abstracts of individual items from the workshop were prepared separately for the data base.
Date: November 1, 1985
Creator: Berkowitz, J.; Berry, H.G. & Berry, R.S. (eds.)
Partner: UNT Libraries Government Documents Department

Ionization phenomena and sources of negative ions

Description: Negative ion source technology has rapidly advanced during the past several years as a direct consequence of the discovery of Krohn that negative ion yields can be greatly enhanced by sputtering in the presence of Group IA elements. Today, most negative ion sources use this discovery directly or the principles implied to effect negative ion formation through surface ionization. As a consequence, the more traditional direct extraction plasma and charge exchange sources are being used less frequently. However, the charge exchange generation mechanism appears to be as universal, is very competitive in terms of efficiency and has the advantage in terms of metastable ion formation. In this review, an attempt has been made to briefly describe the principal processes involved in negative ion formation and sources which are representative of a particular principle. The reader is referred to the literature for specific details concerning the operational characteristics, emittances, brightnesses, species and intensity capabilities of particular sources. 100 references.
Date: January 1, 1983
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Physics with fast molecular ions

Description: Argonne's 5-MV Dynamitron accelerator is currently being used to study the interactions of fast (MeV) atomic and molecular ions with matter. The present emphasis of the work is upon the problem of determining the stereochemical structures of molecular-ion projectiles. The technique is based upon the ''Coulomb explosion'' of these projectiles when they strike a thin-foil target. By making careful determinations of the momenta of all of the fragments emitted from these Coulomb explosions, one can infer the original configuration of the molecular constituents in the projectile and, in favorable cases, their vibrational motions. This technique is particularly useful for those cases where the more traditional spectroscopic approaches cannot be applied. During the past year, new ideas and developments in the Coulomb-explosion technique have come to fruition. Radically new multiparticle detectors have been developed and implemented. Extremely thin film targets have been produced which reduce the ''blurring'' effect of multiple scattering, and a low-excitation ion source has been installed. These developments have resulted in direct measurements of the complete stereostructures of several small polyatomic molecular ions. In this paper we describe the experimental techniques, discuss some of the difficulties, and present some recent results. 19 refs., 5 figs.
Date: January 1, 1987
Creator: Gemmell, D.S.; Faibis, A.; Kanter, E.P.; Vager, Z. & Zabransky, B.J.
Partner: UNT Libraries Government Documents Department

Low energy ion beam systems for surface analytical and structural studies

Description: This paper reviews the use of low energy ion beam systems for surface analytical and structural studies. Areas where analytical methods which utilize ion beams can provide a unique insight into materials problems are discussed. The design criteria of ion beam systems for performing materials studies are described and the systems now being used by a number of laboratories are reviewed. Finally, several specific problems are described where the solution was provided at least in part by information provided by low energy ion analysis techniques.
Date: January 1, 1980
Creator: Nelson, G.C.
Partner: UNT Libraries Government Documents Department

Attractive interaction between an atom and a surface

Description: Using a general self-energy formalism we examine the interaction between an atom and a surface. Considered in detail are deviations from the Van der Waals force due to recoil and finite velocity of the particle. Calculations for positronium near a metal surface show that for such systems recoil and velocity effects are significant even at very low energies. We also examine the mechanisms for energy exchange with the surface and calculations show that single quantum events do not always dominate the exchange rates. 8 references, 2 figures.
Date: January 1, 1983
Creator: Manson, J.R. & Ritchie, R.H.
Partner: UNT Libraries Government Documents Department

Fractional charge search

Description: A device to search for fractional charge in matter is described. The sample is coupled to a low-noise amplifier by a periodically varying capacitor and the resulting signal is synchronously detected. The varying capacitor is constructed as a rapidly spinning wheel. Samples of any material in volumes of up to 0.05 ml may be searched in less than an hour.
Date: June 1, 1982
Creator: Innes, W.; Klein, S.; Perl, M. & Price, J.C.
Partner: UNT Libraries Government Documents Department

Enhanced ion backscattering near 180/sup 0/ scattering angles in the two-atom scattering model. [Ion scattering from solids]

Description: An analytical two-atom scattering model has been developed to treat the recent discovery of the enhancement near 180/sup 0/ of Rutherford backscattering yields from disordered solids. In contrast to conventional calculations of Rutherford backscattering that treat scattering from a single atom only (the backscattering atom), the present model includes the interaction of a second atom lying between the target surface and the backscattering atom. The projectile ion makes a glancing collision with this second atom both before and after it is backscattered. A weighted average is made over all possible positions of this second atom. The model predicts an enhancement effect whose physical origin arises from the tolerance of path for those ions whose ingoing and outgoing trajectories lie in the vicinity of the critical impact parameter. Results using Moliere scattering show how the yield enhancement depends on ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of the projectile and target, and target density. In the model the critical impact parameter and critical angle play important roles. It is shown that these quantities depend on a single dimensionless parameter and formulas accurate to better than 1% are given for them.
Date: August 1, 1982
Creator: Oen, O.S.
Partner: UNT Libraries Government Documents Department

Laser neutralization

Description: Laser photodetachment of the excess electron to neutralize relativistic ions offers many advantages over the more conventional collisional methods using gases or thin foils as the neutralization agents. Probably the two most important advantages of laser photodetachment are the generation of a compact and low divergence beam, and the production of intense neutral beams at very high efficiency (approximately 90%). The high intensities or high current densities of the neutral beam result from the fixed maximum divergence that can be added to the beam by photodetachment of the charge using laser intensity of fixed wavelength and incident angle. The high neutralization efficiency is possible because there is no theoretical maximum to the neutralization efficiency, although higher efficiencies require higher laser powers and, therefore, costs. Additional advantages include focusability of the laser light onto the ion beam to maximize its efficacy. There certainly is no residual gas left in the particle beam path as is typical with gas neutralizers. The photodetachment process leaves the neutral atoms in the ground state so there is no excited state fluorescence to interfere with the subsequent beam sensing. Finally, since the beams to be neutralized are very high powered, for a large range of neutralization efficiencies the neutral beam can be increased more by increasing the power to the laser neutralizer than by adding an equal amount of power to the primary accelerator. 26 figs.
Date: June 17, 1986
Creator: Peterson, O.G.
Partner: UNT Libraries Government Documents Department

Study of electrons photoemitted from field emission tips. Progress report, July 1, 1979-March 1, 1980

Description: Photo-induced field emission is a technique which studies electrons that have been photoemitted from a field emission tip. This new experimental method promises to combine the proven utility of both field emission and photoemission for investigating the electronic states near a metal surface. The primary objective of the research being performed is to investigate photo-induced field emitted electrons using a tuneable cw dye laser. To fully exploit this continuously tuneable photon source, a differential energy analyzer is being constructed to allow energy resolved measurements of the photo-field emitted electrons. This report describes the progress made in implementing experiments on photo-induced field emission from July 1979 to March 1980.
Date: February 1, 1980
Creator: Reifenberger, R.
Partner: UNT Libraries Government Documents Department

Inelastic near-surface interactions. Proceedings of the Werner Brandt workshop

Description: This workshop is one of an annual series covering penetration phenomena of charged particles in matter. This specific workshop includes electron scattering, ion and atom scattering, stopping powers, and cluster ion impacts on solids. Abstracts were prepared for individual items in the proceedings for inclusion in the data base. (GHT)
Date: April 1, 1985
Partner: UNT Libraries Government Documents Department

Practical applications of coherent transition radiation

Description: The predictable nature of transition radiation (TR) emissions has been demonstrated under a wide variety of experimental conditions. The reliable character of TR allows the design of specific practical applications that use emissions from the optical to the x-ray spectral regions. Applications often can be enhanced by the spatial coherence of TR, and some have become highly developed. New applications may be developed through the use of other related radiation mechanisms. 20 refs., 3 figs.
Date: October 2, 1987
Creator: Moran, M.J.
Partner: UNT Libraries Government Documents Department

Test of usable sputter target size in the Florida-State-University-type inverted sputter ion source

Description: Diagrams of the sputter target and plots of beam current as a function of the sputter target size and selected defining aperture are presented in an attempt to determine the smallest sputter target (cone) size usable to obtain reasonable negative ion beams. (JFP)
Date: January 1, 1978
Creator: Billquist, P.J.
Partner: UNT Libraries Government Documents Department

MEVVA ion source for high current metal ion implantation

Description: The MEVVA (Metal Vapor Vacuum Arc) ion source is a new kind of source which can produce high current beams of metal ions. Beams of a wide range of elements have been produced, spanning the periodic table from lithium up to and including uranium. The source extraction voltage is up to 60 kV, and we are increasing this up to 120 kV. A total ion beam current of over 1 Ampere has been extracted from the present embodiment of the concept, and this is not an inherent limit. The ion charge state distribution varies with cathode material and arc current, and beams like Li/sup +/, Co/sup +,2+,3+/ and U/sup 3+,4+,5+,6+/ for example, are typical; thus the implantation energy can be up to several hundred kilovolts without additional acceleration. The ion source has potential applications for ion implantation and ion beam mixing for achievement of improved corrosion resistance or wear resistance in metals or surface modification of ceramic materials and semiconductors. Here we outline the source and its performance, and describe some very preliminary implantation work using this source.
Date: July 1, 1986
Creator: Brown, I. & Washburn, J.
Partner: UNT Libraries Government Documents Department

Gas cell neutralizers (Fundamental principles)

Description: Neutralizing an ion-beam of the size and energy levels involved in the neutral-particle-beam program represents a considerable extension of the state-of-the-art of neutralizer technology. Many different mediums (e.g., solid, liquid, gas, plasma, photons) can be used to strip the hydrogen ion of its extra electron. A large, multidisciplinary R and D effort will no doubt be required to sort out all of the ''pros and cons'' of these various techniques. The purpose of this particular presentation is to discuss some basic configurations and fundamental principles of the gas type of neutralizer cell. Particular emphasis is placed on the ''Gasdynamic Free-Jet'' neutralizer since this configuration has the potential of being much shorter than other type of gas cells (in the beam direction) and it could operate in nearly a continuous mode (CW) if necessary. These were important considerations in the ATSU design which is discussed in some detail in the second presentation entitled ''ATSU Point Design''.
Date: June 1, 1985
Creator: Fuehrer, B.
Partner: UNT Libraries Government Documents Department

Development of a lithium liquid metal ion source for MeV ion beam analysis

Description: Lithium liquid metal ion sources are an attractive complement to the existing gaseous ion sources that are extensively used for ion beam analysis. This is due in part to the high brightness of the liquid metal ion source and in part to the availability of a lithium ion beam. High brightness is of particular importance to MeV ion microprobes which are now approaching current density limitations on targets determined by the ion source. The availability of a lithium beam provides increased capabilities for hydrogen profiling and high resolution Rutherford backscattering spectrometry. This paper describes the design and performance of a lithium liquid metal ion source suitable for use on a 5MV Laddertron accelerator. Operational experience with the source and some of its uses for ion beam analysis are discussed. 8 refs., 2 figs.
Date: January 1, 1988
Creator: Read, P.M.; Maskrey, J.T. & Alton, G.D.
Partner: UNT Libraries Government Documents Department

Pulsed WIP electron gun. Fabrication phase 1 x 40 cm and 1 x 70 cm cooled WIP electron gun. Final report, March 1979-December 1980

Description: An electron gun capable of long-run operation at 10 KHz and 1 A/cm/sup 2/ has been fabricated and tested. Pulse widths of 200 to 600 nsec and a total life of greater than 10/sup 7/ shots have been demonstrated. During the acceptance tests, the electron gun was operated at a total average power of 20 KW for 30 minutes. This basically satisfied the contract requirements. To establish some upper limit of the gun's capability, the device was operated at a repetition rate of 3.5 KHz at a total average power of 54.5 KW for greater than 10 minutes. During these tests, no high voltage breakdown occurred after the device was processed. The beam uniformity at high repetition rates is +-10% and the efficiency is 50%.
Date: January 1, 1980
Creator: Wakalopulos, G.
Partner: UNT Libraries Government Documents Department

Physics of ion sputtering

Description: The ejection of atoms by the ion bombardment of solids is discussed in terms of linear collision cascade theory. A simple argument describes the energies of the ejecta, but elaborate models are required to obtain accurate sputtering yields and related quantities. These include transport theoretical models based on linearized Boltzmann equations, computer simulation models based on the binary collision approximation, and classical many-body dynamical models. The role of each kind of model is discussed. Several aspects of sputtering are illustrated by results from the simulation code MARLOWE. 20 references, 6 figures.
Date: April 1, 1984
Creator: Robinson, M.T.
Partner: UNT Libraries Government Documents Department

LBL EBIS test-strand

Description: An EBIS program was initiated at Lawrence Berkeley Laboratory in late 1979. This first stage, construction of an EBIS research and development test-stand is described, along with results of the bare beam experiments.
Date: May 1, 1981
Creator: Feinberg, B. & Brown, I.G.
Partner: UNT Libraries Government Documents Department

On the Current Intensity Limit of a Vacuum Arc Ion Source

Description: The maximum ion current that can be produced as a high energy beam from a metal vapor vacuum arc ion source is considered. Results are presented of measurements of the plasma ion current in the MEVVA II ion source. It is shown that this source is an efficient generator of metal ions, an intense flux of which is efficiently transported to the beam extractor. The maximum metal ion current that is available for extraction at the extractor location is 5% of the arc current. The limitation to the intensity of the metal ion beam that can be produced by this kind of ion source is in the extractor design. 27 refs., 6 figs.
Date: March 1987
Creator: Brown, I. G.
Partner: UNT Libraries Government Documents Department

Alternative approach to the surface-excitation model

Description: Although the development of the surface-excitation model of sputtered-ion emission involved a detailed description of the ionization process, one can arrive at the same result by assuming an equilibrium treatment, e.g. the Saha-Langmuir equation, with the temperature falling as the collision casade develops. This suggests that, even if situations are found where the surface-excitation model is successful, it does not follow that the original detailed description of the ionization process is correct. Nevertheless, the surface-excitation model does contain an interesting new idea which should not be overlooked, i.e. that atoms sputtered during the early stages of a collision cascade will be relatively energetic, and to the extent that the Saha-Langmuir equation has some applicability, will have a probability of positive ionization which will be low for atoms of low ionization potential (I < phi where I is the ionization potential and phi the work function) and high for atoms of high ionization potential (I > phi), relative to lower-energy atoms emitted during the later stages of the collision cascade. The extended abstract will discuss recent experimental results.
Date: January 1, 1981
Creator: Krohn, V.E.
Partner: UNT Libraries Government Documents Department

Excitation of simple atoms by slow magnetic monopoles

Description: We present a theory of excitation of simple atoms by slow moving massive monopoles. Previously presented results for a monopole of Dirac strength on hydrogen and helium are reviewed. The hydrogen theory is extended to include arbitrary integral multiples of the Dirac pole strength. The excitation of helium by double strength poles and by dyons is also discussed. It is concluded that a helium proportional counter is a reliable and effective detector for monopoles of arbitrary strength, and for negatively charged dyons.
Date: January 1, 1984
Creator: Kroll, N.M.; Parke, S.J.; Ganapathi, V. & Drell, S.D.
Partner: UNT Libraries Government Documents Department