Winthrop W. Smith

New uses of ion accelerators

1. Ion-Excited X-Ray Analysis of Environmental Samples.- I. Introduction.- II. General Considerations for Ion Beam Analysis of Environmental Samples.- III. Formalism and Optimization.- IV. The UCD/ARB Aerosol Analysis System.- A. The Primary Ion Beam.- B. Detection of X-Rays.- C. Data Acquisition and Reduction.- D. System Calibration.- E. Target Preparation and Matrix Effects.- F. Estimation of Analytical Costs.- G. Validation of System Operations.- V. Ion-Excited X-Ray Analysis Programs.- Appendix (Forward Scattering).- Acknowledgments.- References.- 2: Material Analysis by Nuclear Backscattering.- A. Introduction.- General Comments on Nuclear Backscattering.- Appendix (Numerical Examples).- References.- B. Applications.- I. Introduction.- II. Ion Implantation.- III. Thin Films: Growth and Deposition.- IV. Thin Film Reactions: Interdiffusion and Compound Formation.- V. Bulk Effects: Composition, Diffusion and Solubility.- VI. Concluding Remarks.- Acknowledgments.- References.- Formalism.- 1. Three Basic Concepts in Backscattering.- A. Backscattering Kinematic Factor Mass ? Analysis.- B. Differential Scattering Cross Section ? Quantitative Analysis.- C. Energy Loss ? Depth Analysis.- 2. Depth Scale in Backscattering Analysis [S].- A. Depth Scale in Backscattering Analysis.- B. Surface Approximation.- C. Linear Approximation.- 3. Height of an Energy Spectrum.- A. Surface Approximation for Spectrum Height.- B. Thick Target Yield.- C. Backscattering Yield of a Thin Film.- 4. Applications of Backscattering from Elemental Targets.- A. Surface Contamination and Ion Implantation.- B. Doping Level of a Bulk Sample.- C. Film Thickness Measurement and dE/dx Measurements.- D. Yield Formula and dE/dx Measurements.- E. Differential Scattering Cross Section Measurement.- 5. Application of Backscattering to Compound Targets.- A. Thin Film Analysis.- B. Thick Compound Targets.- C. Analysis on Composition Varying Continuously with Depth.- Appendix 1. Notations.- Appendix 2. Formulae.- Appendix 3. Sources for dE/dx Information.- References.- 3: Material Analysis by Means of Nuclear Reactions.- Charged Particle Activation Analysis.- Charged Particle Activation Analysis - Examples.- Prompt Radiation Analysis.- Nonresonant Nuclear Reactions - Gamma Rays Observed.- Nonresonant Nuclear Reactions - Nuclear Particles Observed.- Resonant Nuclear Reactions.- Summary.- Acknowledgment.- References.- 4: Lattice Location of Impurities in Metals and Semiconductors.- I. Introduction.- II. Impurity Detection.- III. The Channeling Technique.- 1. Channeling Concept.- 2. Experimental Technique.- IV. Lattice Location Analysis.- V. Examples.- 1. Substitutional Impurities.- 2. Nearly Substitutional Impurities.- 3. Interstitial Impurities.- 4. High Impurity Concentrations.- 5. Radiation-Induced Change in Impurity Sites.- VI. Summary of the Literature on Channeling Lattice Location Data.- VII. Limitations.- VIII. Conclusions.- References.- 5: Ion Implantation in Metals.- Historical Perspective.- Friction and Wear.- Corrosion.- 1. Oxides with Anion Defects.- 2. Oxides with Cation Defects.- Ion Backscattering.- Titanium and Stainless Steel.- Zirconium.- Aluminum.- Copper.- Aqueous Corrosion.- Practical Applications in Corrosion.- Electrochemistry and Catalysis.- Implantation Metallurgy.- Equipment for the Ion Implantation of Metals.- Conclusions.- References.- 6: Ion Implantation in Superconductors.- Definition of the Superconducting Parameters.- Influence of Radiation Damage on the Superconducting Properties.- a. Non-Transition Metals.- b. Transition Metals.- c. Transition Metal Alloys.- d. Superconductors with A-15 and NaCl-Structure.- e. Transition Metal Layer Compounds.- f. Quantitative Estimation of Damage in Superconductors.- Influence of Implanted Ions on the Superconducting Transition Temperature.- a. Magnetic Impurities in Non Transition Metals.- b. Pd-, Pd-Noble Metal Alloy, -Hydrogen System.- c. Ion Implanted Transition Metal Systems.- d. Aluminum Based Ion Implanted Systems.- Application to Superconducting Devices.- Conclusions.- References.- 7: Ion-Induced X-Rays from Gas Collisions.- 1. Introduction.- 2. Collision Models.- 2.1. Survey of Models.- 2.2. Coulomb Ionization.- 2.3. The Molecular-Orbital Model.- 3. Measurements of Inner-Shell Excitations.- 3.1. Introduction.- 3.2. Theory of Energy-Loss Measurements.- 3.3. X-Ray and Electron Emission.- 3.4. Typical Apparatus-Ionization and Inelastic Energy Loss.- 3.5. Scattered- Ion-X-Ray/Electron Coincidence Apparatus.- 4. Discussion of Typical Data.- 4.1. Ionization States.- 4.2. Inelastic Energy Loss.- 4.3. Electron Emission Cross Sections.- 4.4. Fluorescence Yield Effects.- 4.5. X-Ray-Scattered-Ion Coincidence Data.- 4.6. X-Rays from Highly Stripped Fast Ion Beams.- 5. Summary.- References.- 8: Ion-Induced X-Rays in Solids.- 1. Introduction.- 2. Accelerators and Target Chambers.- 2.1. Ion Sources.- 2.2. Target Chambers.- 3. The Detection and Analysis of X-Rays.- 3.1. The Gas Flow Proportional Counter.- 3.2. The Si(Li) Detector.- 3.3. The X-Ray Crystal or Grating Spectrometer.- 4. The Use of Protons and Helium Ions to Generate X-Rays from Solid Targets.- 4.1. Current Areas of Fundamental Interest.- 4.2. Applications.- 5. The Use of Heavy Ions to Generate X-Rays from Solid Targets.- 5.1. General Background.- 5.2. Physical Processes.- 5.3. Applications.- 6. Conclusions.- References.- Author Index.

Cold ion–neutral collisions in a hybrid trap

A dual hybrid ion–neutral trap has been built to study collisions between a cloud of ultracold atoms and small numbers of co-trapped atomic or molecular ions, in a common volume. Ultracold Na atoms are trapped in a vapour-cell magneto-optical trap (MOT), via a single-mode frequency-stabilized ring-dye laser, with repumping. A linear rf quadrupole Paul ion trap, centred on the MOT, co-traps selected atomic or molecular ions, for example Ca+. Control of the initial ion temperature involves laser cooling Ca+ ions via the resonant Fraunhofer K line at 397u2009nm. We showed the rf ion trap can operate simultaneously with the MOT without destroying the ultracold atom cloud. The goal is to investigate the physics of ion–neutral sympathetic cooling, the cooling by neutrals of translationally cold and vibrorotationally hot molecular ions (e.g. Na2 +(v*, J*)), and the observation of other ion–neutral processes near 0u2009K, of potential interest in astrophysics.

Triatomic associative ionization: Na+3 formation

Abstract We observe the production of Na+3 ions in a single effusive sodium atomic beam via intra-beam, associative ionization collisions of laser-excited Na(4d, 5s) atoms with ground state Na2 dimers present in the beam: Na(4d, 5s) + Na2→Na+3 + e−. The cross section ratio of this reaction to the corresponding atomic associative ionization collision, Na(4d, 5s)+(Na(3s)→Na+2+e−, has been determined to be 2.0 for Na(4d) and 10.0 for Na(5s) at relative collision velocities of approximately 500 m/s.

Associative ionization in laser-excited sodium 3p+3d collisions

Abstract Collisions of laser-excited Na(3p) and stepwise laser-excited Na(3d) atoms in a single effusive atomic beam have been observed to result in Na 2 + ion formation: Na(3p)+Na(3d)→Na 2 + +e − . The cross-section for this process is measured to be approximately 15 times larger than the familiar Na(3p)+Na(3p)→Na 2 + +e − associative ionization reaction, at relative collision velocities of approximately 300 m/s. Theoretical models discussed here are qualitatively consistent with the experimental results.

Spectra from multiphoton electron detachment of H

New data are reported on the multiphoton detachment process in a fast beam of H− ions. The angle-tuned relativistic Doppler shift is used to vary the photon energy of a focused (~10 GW/cm2) 10.6-μm CO2 laser beam from ~0.05 to ~0.4 eV in the rest frame (CM frame) of the fast ions. The ions are produced at 800 MeV (β = v/c = 0.84) by the Los Alamos Meson Physics Facility linear accelerator at Los Alamos and experience ~1-psec pulses in the CM frame as they cross the laser beam focus. Peaks in the detachment signal corresponding to each order for two- to six-photon processes are observed. At modest laser intensity in the gigawatt-per-square-centimeter range, observed shifts of the apparent two-photon threshold are found to be not more than 30–50% of the expected maximum shift, based on the value of the ponderomotive potential. Experimental uncertainties are due mainly to imprecise knowledge of the maximum laser intensity. The data analysis and modeling of the expected threshold shape experiments are continuing.

Electron spectroscopy of foil-excited chlorine beams☆

Abstract We report on a recent spectroscopic study of autoionization electrons emitted by fast, foil-excited chlorine ion beams. The observed electrons originated in the decay of certain core-excited metastable autoionizing states in lithium-like and sodium-like chlorine. Such states are metastable since they are forbidden to autoionize via the strong Coulomb interaction but decay instead via second-order magnetic interactions (or in some cases, radiatively). Chlorine beams from the Oak Ridge tandem accelerator were passed through thin carbon foils (≈ 15 μg/cm2) which served both to strip and excite the ions. Electrons emitted in the decay of autoionizing states thus formed were energy analyzed after the foil by a cylindrical mirror analyzer, the position of which could be varied with respect to the foil to facilitate time-of-flight lifetime studies. Beam energies were chosen to maximize the production of the lithium-like (Cl14+) and sodium-like (Cl6+) charge states. The results of a measurement of the energy and the lifetime of the (1s2s2p) 4 P 5 2 state of Cl14+ will be presented. A spectrum of autoionization electrons from Cl6+ will also be shown, but firm identification of many of the states of this system is at present difficult due to the almost complete lack of theoretical calculations of the energies and lifetimes of such states.

Laser Spectroscopy of Relativistic Beams of H- and H: Observation of e-Detachment from H- by Multiphoton Absorption

Publisher Summary This chapter discusses laser spectroscopy of relativistic beams of H- and H by multiphoton absorption. Multiphoton detachment (MPD) takes place with lower energy photons than typical multiphoton ionization (MPI) with neutrals. The lack of intermediate-states simplifies the calculations as does the fact that the final-state interaction is of short range rather than Coulomb: H- may provide a particularly clean test of MPI/MPD theory. Large changes in the MPD rate can be expected when a large static electric field is applied in addition to a laser field. In the experiment described in the chapter, detached electrons were detected with high efficiency and low background by the electron spectrometer; fast η atoms were detected by a downstream scintillator. Observed MPD rates with the smoothing tube were somewhat smaller than without it, as expected, but at the highest intensities, partial depletion saturation was observed of at least the 3-photon threshold detachment on the ∼1 psec scale of the H- transit time through the laser focus.

Metastable States of Highly Excited Heavy Ions

Highly stripped heavy ions (i.e. systems with high nuclear charge but a small number of electrons) are of interest from several viewpoints. One reason is that the relativistic magnetic interactions such as the spin-orbit, spin-other-orbit and spin-spin interactions are considerably stronger in these ions than in nearly neutral isoelectronic ions. This situation sometimes allows “forbidden” processes to be experimentally observable, even though the rates for these processes are still very small compared to those for “allowed” processes. A number of recent experiments1 involving the radiative decay of metastable states of highly stripped ions have advanced our knowledge of atomic structure through a comparison of radiative decay rate measurements with theory. It is also possible to study metastable states in simple heavy ions which do not decay radiatively, but by the autoionization processes instead. Our recent work2 concerns the study of such states.