A5022736240- Atomic and Molecular Physics
- Advanced Chemical Physics Studies
- Electron and X-Ray Spectroscopy Techniques
- Photocathodes and Microchannel Plates
- Atomic and Subatomic Physics Research
- X-ray Spectroscopy and Fluorescence Analysis
- Mass Spectrometry Techniques and Applications
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum and electron transport phenomena
- Advanced Electron Microscopy Techniques and Applications
- Quantum, superfluid, helium dynamics
- Quantum optics and atomic interactions
- Particle accelerators and beam dynamics
- Ion-surface interactions and analysis
- Nuclear Physics and Applications
- Dark Matter and Cosmic Phenomena
- Laser-induced spectroscopy and plasma
- Radiation Therapy and Dosimetry
- Particle physics theoretical and experimental studies
- Plasma Diagnostics and Applications
- Spectroscopy and Laser Applications
- Laser-Matter Interactions and Applications
- Experimental and Theoretical Physics Studies
- Astro and Planetary Science
- Spectroscopy and Quantum Chemical Studies
University of Nebraska–Lincoln
2015-2024
Thomas Jefferson National Accelerator Facility
2014
George Washington University
2014
University of Virginia
1986-2014
Hunter Water
2012
Brandeis University
2011
California State University, Fullerton
2001
Drake University
1997
Missouri University of Science and Technology
1987-1996
Australian National University
1996
All known data on the energy distribution of secondary electrons from collisions protons with atoms and molecules have been reviewed differential cross sections collected. The two experimental methods used to obtain are discussed possible sources error pointed out. Theoretical treatments several checking consistency discussed. Two semiempirical models chosen represent sections, parameters for these given which fit average data, subject constraints. Recommended values ten target gases by means models.
Electron polarimeters based on Mott scattering are extensively used in atomic and molecular, solid state, nuclear, high-energy physics. This use stems from the increasing realization that much additional information concerning many physical processes can be obtained through spin-dependent measurements. In this review we discuss basic physics application of polarimetry. A number different polarimeter designs described illustrate wide range operating energies (10 eV–1 MeV) geometries such...
We have studied ${\mathrm{H}}^{+}$+He ionizing collisions, and find that electrons stranded between the two postcollision Coulomb centers dominate ejected-electron spectra for intermediate (\ensuremath{\sim}100 keV) projectile energies. The importance of these is clearly established by our classical calculations which are in qualitative agreement, both shape magnitude, with experimental taken us, earlier measurements. These ``saddle-point'' produced a classically understandable mechanism,...
We have measured the parity-violating electroweak asymmetry in elastic scattering of polarized electrons from $^{12}\mathrm{C}$ nuclei. Our result is ${\mathit{A}}_{\mathrm{expt}}$=0.60\ifmmode\pm\else\textpm\fi{}0.14\ifmmode\pm\else\textpm\fi{}0.02 ppm, where first error statistical and second systematic. With a beam polarization 0.37, we compute isoscalar vector hadronic coupling constant \ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{} to be...
Experiments show that beams of left- or right-handed electrons are not equal-opportunity destroyers molecules having two mirror-image forms, which supports the idea primordial cosmic rays generated asymmetry in biological molecules.
We have made a systematic study of rubidium optical pumping in simple cylindrical cell geometry with high-power $10\phantom{\rule{0.3em}{0ex}}\mathrm{W}$ diode laser array, low magnetic fields, and buffer-gas pressures less than $50\phantom{\rule{0.3em}{0ex}}\text{torr}$. determined polarizations experimentally for ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, He, Ar buffer gases, Rb number densities from...
The conflict between Bohr's assertion that the magnetic moment of electron cannot be measured with experiments based on concept classical trajectories, and measurement electrons in a modified Penning trap by Dehmelt et al. has led us to reevaluate other implications assertion. We show that, contrary analysis Bohr Pauli, assumption trajectories Stern-Gerlach--like device can result high degree spin separation for an beam. This effect may persist within fully quantum-mechanical analysis....
In order to understand some of the systematic effects associated with conventional Mott-scattering electron polarization measurements, we analyzed asymmetry data obtained 94-keV polarized electrons scattered at 120\ifmmode^\circ\else\textdegree\fi{} from gold-foil targets ranging in thickness 27 62 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$. Based upon an examination influence multiple and plural scattering, conclude that precision such Mott measurements is fundamentally limited by experimental...
We have studied ${\mathrm{H}}^{+}$+He and $^{3}\mathrm{He}^{++}$+He ionizing collisions at intermediate energies (60 to 120 keV/amu) observed a significant shift in the velocity position of maxima forward-ejected electron spectra when changing projectiles from protons \ensuremath{\alpha} particles. In collisions, large portion ejected electrons are stranded near transitory equiforce, or saddle point, between target ion receding projectile. The smaller velocities, due particles, is consistent...
We have measured the integrated Stokes parameters of light emitted following impact excitation by polarized electrons ${\mathit{np}}^{5}$ (n+1)p[5/2${]}_{3}$ states in Ne (n=2), Ar (n=3), Kr (n=4), Xe (n=5), and (n+1)p[5/2${]}_{2}$ state Kr. The near-threshold linear-polarization fractions ${\mathrm{\ensuremath{\eta}}}_{1}$ were consistent with zero for all J=3 measured, providing no evidence Mott scattering. For J=2 excitation, shows clear influence intermediately coupled nature state. At...
In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A values they would have for scattering from single atoms. These extrapolations involve dependence of on either thickness t or maximum detected energy loss in target ΔE. Using a concentric cylindrical-electrode polarimeter, we studied and compared these two types over range 20–100 keV. The potential systematic errors which can result such...
Classical-trajectory Monte Carlo calculations have been used to study ionizing collisions between charged particles ($p,\overline{p},{e}^{+},{e}^{\ensuremath{-}}$) and He atoms at an incident velocity of 2.83 a.u. While differences in the total single-ionization cross sections for these projectiles are small, our reveal large effects all angles ionized electron spectra, provide qualitative evidence a Barkas effect $p$ $\overline{p}$ collisions. Experimental data agree well with fully...
Laser light with photon energy near the band gap of GaAs and in Laguerre-Gaussian modes different amounts orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree electron spin polarization measured using a micro-Mott polarimeter found be consistent zero an upper limit \ensuremath{\sim}3$%$ for up $\ifmmode\pm\else\textpm\fi{}5\ensuremath{\hbar}$ momentum. In contrast, 32.3 \ifmmode\pm\else\textpm\fi{} 1.4$%$ circularly polarized laser at as same...
A polarized electron source, based on photoemission from GaAs, has been developed and installed at the MIT Bates Linear Accelerator Center. multichamber vacuum system houses up to four GaAs crystals simultaneously, is contained in a Faraday cage provide about 300 keV electrostatic acceleration. modulated cw krypton ion laser used achieve stable operation during 15 μs pulses with repetition rate of 600 Hz. The source produced pre-injected peak currents excess 17 mA, accelerated 8 mA....
It is pointed out that heavy atoms (i.e. those which have spectroscopically resolvable fine structure) are not required for optical measurements of electron polarisation. A polarimeter uses helium gas instead heavy-metal vapour proposed, and several experimental details discussed.
We have measured the dependence upon target-foil temperature of linear polarization fraction ($\frac{M}{I}$) $2s^{1}S\ensuremath{-}3p^{1}P$, 5016-\AA{} transition in He i for ion energies between 60 and 180 keV. The thin carbon exciter foils were heated externally by Nichrome resistance elements. measurements Hight et al. are duplicated; energy current dependencies $\frac{M}{I}$ same, assuming correspondence beam heating external heating. also observe that $\ensuremath{\gamma}$, number...
We present the results of a rigorous quantum-mechanical calculation propagation electrons through an inhomogeneous magnetic field with axial symmetry. A complete spin polarization beam is demonstrated assuming that Landau eigenstate can be inserted into field. This in contrast semiclassical situation, where splitting blurred.
Energy spread and extracted current measurements are presented for five different types of ion sources: hot cathode, cold magnetron, microwave, electron cyclotron resonance (ECR). The were performed with a 45° parallel-plate energy analyzer resolution better than 0.5 eV at 500 incident energy. spreads ranged from to 4 eV, while total beam currents 2 30 μA. Beam due specifically protons, 3He++ ions, H+2 ions also presented. ECR magnetron sources gave the best overall performance. These, along...
The spectra of electrons emitted in collisions between H+ and He2+ projectiles He, Ne Ar targets at energies 50 100 keV amu-1 have been studied. data are qualitative agreement with results Irby el al. (1988), but disagreement measurements Bernardi et (1989, 1990). It is shown that the observed electron a dependence on both target-ion projectile effective charge can be understood qualitatively terms 'saddle-point' ionization. Several issues relevant to saddle-point ionization discussed.
We report on the design and performance of a Mott polarimeter optimized for nominal 5-MeV electron beam from Continuous Electron Beam Accelerator Facility (CEBAF) injector. The rf time structure this allows use flight in scattered detection, making it possible to cleanly isolate those detected electrons that originate scattering foil, resulting measured asymmetries which are exceptionally stable over broad range conditions, currents, foil thicknesses. In two separate series measurements...
Using a Fano-effect polarized electron source and state-selected thermally dissociated hydrogen beam, we measured the interference between direct exchange scattering amplitudes for electron-impact ionization of atomic 14.1 30.3 eV. We report data from these measurements results corrections applied to previously published data.
We have studied dissociative electron attachment (DEA) between low energy ($\ensuremath{\le}0.6\text{ }\text{ }\mathrm{eV}$) longitudinally polarized electrons and gas-phase chiral targets of 3-bromocamphor (${\mathrm{C}}_{10}{\mathrm{H}}_{15}\mathrm{BrO}$), 3-iodocamphor (${\mathrm{C}}_{10}{\mathrm{H}}_{15}\mathrm{IO}$), 10-iodocamphor. The DEA rate depends on the sign incident helicity for a given target handedness, it varies with both atomic number ($Z$) location heaviest atom in...
The statistical character of electron beams used in current technologies, as described by a stream particles, is random nature. Using coincidence measurements femtosecond pulsed pairs, we report the observation sub-Poissonian statistics that are nonrandom due to two-electron Coulomb interactions, and exhibit an antibunching signal 1 part 4. This advancement fundamental step toward observing strongly quantum degenerate beam needed for many applications, particular correlation spectroscopy.
We have measured the polarization of fluorescence emitted by noble gases He, Ne, Ar, Kr, and Xe following impact excitation polarized electrons. In ${3}^{3}$P\ensuremath{\rightarrow}${2}^{3}$S transition was studied; in heavy ${\mathit{np}}^{5}$(n+1)p${\mathrm{}}^{3}$${\mathit{D}}_{3}$\ensuremath{\rightarrow}${\mathit{np}}^{5}$(n+1)s${\mathrm{}}^{3}$${\mathit{P}}_{2}$ transitions were analyzed. investigated these as candidates for efficient optical electron polarimetry found that, because...