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The Scattering of Positrons by Atomic Hydrogen: Formulation

Description: The derivation of the coupled systems of second-order integrodifferential equations which must be solved numerically in order to obtain the cross sections for the elastic and inelastic scattering of positrons by atomic hydrogen and the cross sections for the formation of positronium into the 1s and 2s states is considered. The numerical method to be used to solve the equations at incident energies above excitation thresholds is also discussed. (auth)
Date: October 1, 1960
Creator: Cody, W. J. & Smith, K.
Partner: UNT Libraries Government Documents Department

Vacancy Clusters at Nanoparticle Surfaces

Description: The authors detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v{sub 4}) are attached to the gold nanoparticle surfaces within the projected range (R{sub p}).
Date: August 6, 2000
Creator: Xu, J.; Moxom, J.; Somieski, B.; White, C.W.; Mills, A.P.; Suzuki, R. et al.
Partner: UNT Libraries Government Documents Department

Oncogene mRNA Imaging with Radionuclide-PNA-Peptides

Description: New cancer gene hybridization probes to carry radionuclides were made. Noninvasive technetium-99m gamma imaging of CCND1 cancer gene activity in human breast cancer tumors in mice was demonstrated, followed by noninvasive technetium-99m imaging of MYC cancer gene activity. Noninvasive imaging of CCND1 cancer gene activity in human breast cancer tumors in mice was demonstrated with a positron-emitting copper-64 probe, followed by noninvasive positron imaging of IRS1 cancer gene activity.
Date: March 19, 2008
Creator: Wickstrom, Eric
Partner: UNT Libraries Government Documents Department

Particle-in-Cell Calculationsof the Electron Cloud in the ILCPositron Damping Ring Wigglers

Description: The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ILC positron damping ring wiggler. WARP is a parallelized, 3D particle-in-cell code which is fully self-consistent for all species. The POSINST models for the production of photoelectrons and secondary electrons are used to calculate electron creation. Mesh refinement and a moving reference frame for the calculation will be used to reduce the computer time needed by several orders of magnitude. We present preliminary results for cloud buildup showing 3D electron effects at the nulls of the vertical wiggler field. First results from a benchmark of WARP-POSINST vs. POSINST are also discussed.
Date: July 1, 2007
Creator: Celata, C.M.; Furman, M.A.; Vay, J.-L. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

THREE NEW DELAYED ALPHA EMITTERS OF LOW MASS

Description: Two new positron active isotopes, B{sup 8} and Na{sup 20}, have been found to decay to excited states of Be{sup 8} and Ne{sup 20}, which in turn decay 'instantaneously' by alpha emission. Their half-lives are 0.65 {+-} 0.1 sec. and 1/4 sec. respectively. N{sup 12} is also found to have a low energy positron group which leads to an {alpha}-unstable excited state in C{sup 12}. The masses of B{sup 8} and Na{sup 20} are 8.027 and 20.015 respectively. B{sup 8} decays by a 13.7 {+-} 0.3 Mev positron, through the same excited state of Be{sup 8} as does Li{sup 8}. Estimates of the energies of the excited state in C{sup 12} and Ne{sup 20} are made.
Date: May 31, 1950
Creator: Alvarez, Luis W.
Partner: UNT Libraries Government Documents Department

An Asymmetric B-Meson Factory at PEP

Description: A preliminary design for a B-factory has been made using asymmetric collisions between positrons in the PEP storage ring and electrons in a new, low-energy ring. The design utilizes small-aperture, permanent-magnet quadrupoles close to the interaction point (IP). Optimization of optical and beam parameters at the IP will be discussed, as well as the lattice design of the interaction region and of the rings.
Date: January 1, 1990
Creator: Garren, A.A.; Chattopadhyay, S.; Chin, Y.; Oddone, P.J.; Zisman, Michael S.; Donald, M. et al.
Partner: UNT Libraries Government Documents Department

A Preliminary Low-Frequency Electromagnetic Analysis of a Flux Concentrator

Description: The objective of this investigation was to conduct a quick, preliminary transient magnetostatic analysis of a Brechna-type[1] flux concentrator to determine its feasibility for collecting positrons in the International Linear Collider. The magnetostatic transient module of Maxwell 3D, Version 10, from the Ansoft Corporation was used to model the flux concentrator.
Date: June 7, 2006
Creator: Mayhall, D J
Partner: UNT Libraries Government Documents Department

Products of High-Energy Deuteron and Helium Ion Bombardments of Copper

Description: The identity and relative yields of about twenty of the radioisotopes produced by the bombardment of natural copper with 190 Mev deuterons and 380 Mev helium ions have been determined. Two previously unreported isotopes were detected: Zn{sup 62}, decaying by orbital electron capture with a 9.5-hour half-life, and Fe{sup 52}, decaying by positron emission with a 7.8-hour half-life.
Date: March 1, 1948
Creator: Miller, D.R.; Thompson, R.C. & Cunningham, B.B.
Partner: UNT Libraries Government Documents Department

Summary of beam quality diagnostics and control working group

Description: The working group on beam quality, diagnostics, and control at the 12th Advanced Accelerator Concepts Workshop held a series of meetings during the Workshop. The generation of bright charged-particle beams (in particular electron and positron beams), along with state-of-the-art beam diagnostics and synchronization were discussed.
Date: September 1, 2006
Creator: Lewellen, John & Piot, Philippe
Partner: UNT Libraries Government Documents Department

Capture - Positron Ratios for Allowed and First-Forbidden Transitions

Description: Report issued by the Brookhaven National Laboratory discussing capture positron ratios. As stated on page 1, "the purpose of this report is to present aids for the simple determination of the relative probabilities of K-electron capture and positron emission for allowed and first-forbidden transitions" (p. 1). This report includes tables, and illustrations.
Date: January 1958
Creator: Perlman, M. L. & Wolfsberg, Max
Partner: UNT Libraries Government Documents Department

Calculation of positron observables using a finite-element-based approach

Description: We report the development of a new method for calculating positron observables using a finite-element approach for the solution of the Schrodinger equation. This method combines the advantages of both basis-set and real-space-grid approaches. The strict locality in real space of the finite element basis functions results in a method that is well suited for calculating large systems of a thousand or more atoms, as required for calculations of extended defects such as dislocations. In addition, the method is variational in nature and its convergence can be controlled systematically. The calculation of positron observables is straightforward due to the real-space nature of this method. We illustrate the power of this method with positron lifetime calculations on defects and defect-free materials, using overlapping atomic charge densities.
Date: November 4, 1998
Creator: Klein, B. M.; Pask, J. E. & Sterne, P.
Partner: UNT Libraries Government Documents Department

Lifetime studies at the APS.

Description: The studies presented in this note are focused on the lifetime characterization with positrons for the symmetrical low {beta}{sub y} lattice. Before switching back to electrons, detailed lifetime studies were performed in order to gather data that could be compared to similar ones with electrons, the ultimate goal being to define a model that could be used to predict lifetimes. The report is divided into three parts: simulations to allow decoupling of the different contributions to the lifetime; review of the experimental conditions and related problems; and analysis of the data and discussion of the limitations.
Date: May 7, 1999
Creator: Ropert, A.
Partner: UNT Libraries Government Documents Department

THE USE OF POSITRON EMISSION TOMOGRAPHY IN IDENTIFYING AND QUANTIFYING RECEPTORS INVOLVED IN SCHIZOPHRENIA.

Description: Schizophrenia is a devasting mental disorder that is the focus of a great deal of research. Some symptoms of the disease, such as auditory hallucinations and delusions, can be ameliorated with drug treatment, whereas other symptoms, such as social withdrawal and cognitive decline, remain uncontrolled. It is possible that these latter symptoms that are often termed ''negative symptoms'' are the result of anatomical and neurochemical abnormalities, whereas those symptoms of the disease such as auditory hallucinations that are termed ''positive symptoms'' may be a result of only neurochemical disorders. The drugs used to treat schizophrenia are designated neuroleptics. The term neuroleptic was chosen to emphasize the similarity of pharmacological profiles of drugs with entirely different chemical structures. Especially prominent features of the effects of neuroleptics include the following: a state of affective indifference; a decrease in locomotor activity; a decrease in excitation, agitation, and aggressiveness; and an antipsychotic action in patients with acute as well as chronic psychoses.
Date: January 1991
Creator: Volkow, N. D. & Wolf, A. P.
Partner: UNT Libraries Government Documents Department

A positron accumulator ring for APS

Description: The new positron injection scheme is as follows. The cycle rate of the injector synchrotron is increased to 2 Hz. During 0.4 sec of each 0.5-sec synchrotron cycle, 24 linac pulses are injected into the horizontal phase space of the PAR at a 60-Hz rate. Each injected pulse occupies about 1/3 of the circumference of the accumulator ring. After 0.1 sec for longitudinal damping, the single accumulated bunch is transferred into one of the 352.96-MHz buckets of the injector synchrotron RF system. This single bunch is accelerated to 7 GeV and transferred into the storage ring while the PAR accumulates the next bunch of positrons. The injector synchrotron requires only the one high-frequency RF system.
Date: March 1, 1988
Creator: Crosbie, E.A.
Partner: UNT Libraries Government Documents Department

Final Technical Report: "New Tools for Physics with Low-energy Antimatter"

Description: The objective of this research is to develop new tools to manipulate antimatter plasmas and to tailor them for specific scientific and technical uses. The work has two specific objectives. One is establishing the limits for positron accumulation and confinement in the form of single-component plasmas in Penning-Malmberg traps. This technique underpins a wealth of antimatter applications. A second objective is to develop an understanding of the limits for formation of cold, bright positron beams. The research done in this grant focused on particular facets of these goals. One focus was extracting tailored beams from a high-field Penning-Malmberg trap from the magnetic field to form new kinds of high-quality electrostatic beams. A second goal was to develop the technology for colder trap-based beams using a cryogenically cooled buffer gas. A third objective was to conduct the basic plasma research to develop a new high-capacity multicell trap (MCT) for research with antimatter. Progress is reported here in all three areas. While the goal of this research is to develop new tools for manipulating positrons (i.e., the antiparticles of electrons), much of the work was done with test electron plasmas for increased data rate. Some of the techniques developed in the course of this work are also relevant to the manipulation and use of antiprotons.
Date: October 2, 2013
Creator: Surko, Clifford M.
Partner: UNT Libraries Government Documents Department

Transverse Beam Emittance Measurements of a 16 MeV Linac at the Idaho Accelerator Center

Description: A beam emittance measurement of the 16 MeV S-band High Repetition Rate Linac (HRRL) was performed at Idaho State University's Idaho Accelerator Center (IAC). The HRRL linac structure was upgraded beyond the capabilities of a typical medical linac so it can achieve a repetition rate of 1 kHz. Measurements of the HRRL transverse beam emittance are underway that will be used to optimize the production of positrons using HRRL's intense electron beam on a tungsten converter. In this paper, we describe a beam imaging system using on an OTR screen and a digital CCD camera, a MATLAB tool to extract beamsize and emittance, detailed measurement procedures, and the measured transverse emittances for an arbitrary beam energy of 15 MeV.
Date: July 1, 2012
Creator: S. Setiniyaz, T.A. Forest, K. Chouffani, Y. Kim, A. Freyberger
Partner: UNT Libraries Government Documents Department

Nitrogen 12

Description: N{sup 12} is shown to have a half life of 12.5 {+-} 1 milliseconds, and a positron upper limit of 16.6 {+-} 0.2 Mev. It is produced by the reaction C{sup 12}(p,n)N{sup 12}, and has a threshold proton energy of 20.0 Mev. This indicates that N{sup 12} is within about 200 Kev of being unstable against proton emission. The mass of N{sup 12} is 12.0228 {+-} 0.00015, and the beta transition is allowed.
Date: January 19, 1949
Creator: Alvarez, Luis W.
Partner: UNT Libraries Government Documents Department

INTERNAL CONVERSION COEFFICIENTS - HOW GOOD ARE THEY NOW?

Description: Internal conversion coefficients involving atomic electrons (ICC) and electron-positron pairs (IPC) are often required to determine transition multipolarities and total transition rates. A new internal conversion coefficient data base, BrIcc has been developed which integrates a number of tabulations on ICC and IPC, as well as {Omega}(E0) electronic factors. To decide which theoretical internal conversion coefficient table to use, the accurately determined experimental {alpha}{sub K}, {alpha}{sub L}, {alpha}{sub Total} and {alpha}{sub K}/{alpha}{sub L} values were compared with the new Dirac-Fock calculations using extreme assumptions on the effect of the atomic vacancy. While the overall difference between experiment and theory is less than 1%, our analysis shows preference towards the so called ''Frozen Orbital'' approximation, which takes into account the effect of the atomic vacancy.
Date: April 22, 2007
Creator: KIBEDI,T.; BURROWS, T.W.; TRZHASKOVSKAYA, M.B.; NESTOR, JR., C.W. & DAVIDSON, P.M.
Partner: UNT Libraries Government Documents Department

Luminosity Lifetime

Description: In a symmetric or 'energy transparent' relativistic collider, the luminosity is given by L = N{sup 2}f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y} where N is the number of electrons or positrons per bunch, {sigma}*{sub x} ({sigma}*{sub y}) is the horizontal (vertical) rms beam size at the interaction point (IP), and f{sub c} is the collision frequency. If the beam sizes remain constant as the luminosity decreases, then the time dependence of luminosity is contained entirely in the time dependence of the beam currents, i.e., N O N(t), and we can rewrite the equation as L(t) = N{sup 2}(t)f{sub c}/4{pi}{sigma}*{sub x}{sigma}*{sub y}. There are two distinct categories for luminosity loss. In the first category are loss processes due to collisions between the two beams, that is, processes associated directly with the luminosity. In the second category (see below) are single-beam loss processes. The processes in the first category relevant to a high-energy collider are Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}) and 'radiative' Bhabha scattering (e{sup +}e{sup -} O e{sup +}e{sup -}{gamma}). In the first process, a beam particle is lost if its angular deflection is beyond the ring's transverse acceptance; in the second process, loss occurs if the beam particle's momentum change is outside the longitudinal acceptance of the ring (typically determined by the RF bucket height).
Date: April 1, 1997
Creator: Zisman, M.S.
Partner: UNT Libraries Government Documents Department

Atomic Structure of Pyramidal Defects in GaN:Mg; Influence ofAnnealing

Description: The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Defects in bulk GaN:Mg were almost one order of magnitude larger than in thin films. An exchange of Ga and N sublattices within the defect compared to the matrix lead to a 0.6 {+-} 0.2 {angstrom} displacement between the Ga sublattices of these two areas. A [1100]/3 shift with change from AB stacking in the matrix to BC within the entire pyramid was observed. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the photoluminescence intensity. Positron annihilation confirms presence of vacancies of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 C.
Date: October 3, 2005
Creator: Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; O'Keefe, M.; Hautakangas, S.; Saarinen, K. et al.
Partner: UNT Libraries Government Documents Department

On Asymmetric Collisions with Large Disruption Parameters

Description: Collisions between a weak electron bunch and a strong positron bunch are studied within a flat beam model. Electrons are tracked through the transverse space charge field of the positron bunch, and it is shown that positrons in a storage ring may remain stable after asymmetric collisions with a weak electron bunch in spite of large values of the electron disruption parameter. The plasma oscillations that effect collisions with large disruption parameters may be suppressed by properly matching the electrons.
Date: June 1, 1990
Creator: Krafft, Geoffrey; Fripp, Michael & Heifets, Sam
Partner: UNT Libraries Government Documents Department

Electron Positron Proton Spectrometer for use at Laboratory for Laser Energetics

Description: The Electron Positron Proton Spectrometer (EPPS) is mounted in a TIM (Ten-Inch Manipulator) system on the Omega-60 or Omega-EP laser facilities at the University of Rochester, Laboratory for Laser Energetics (LLE), when in use, see Fig. 1. The Spectrometer assembly, shown in Fig. 2, is constructed of a steel box containing magnets, surrounded by Lead 6% Antimony shielding with SS threaded insert, sitting on an Aluminum 6061-T6 plate.
Date: April 7, 2010
Creator: Ayers, S L
Partner: UNT Libraries Government Documents Department