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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

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

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

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

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

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

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

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 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

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

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

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

Slow positron target concepts for the Advanced Photon Source (APS) linear accelerator

Description: The APS linear accelerator (linac) system consists of a 200-MeV, 2856-MHz S-band electron linac, followed by a 450-Mev positron linac. The linac is available for other uses upon completion of the storage ring injection cycle. Nominal linac beam power is 480 W but the power can be increased substantially, making it suitable for production of slow positrons. Simulation studies for the design of a slow-positron target-moderator system that is optimized for operation with the APS linac are presented. Results of simulations of various target configurations indicate that a suitably designed multilayer target can result in a higher positron yield than a single-block target. Use of an integrated, multilayer target moderator is suggested. Some possibilities for extracting slow positrons between target layers by means of electromagnetic fields are discussed. First results from recent accelerator studies aimed at increasing the linac beam power are also presented.
Date: September 1, 1997
Creator: White, M. & Lessner, E.
Partner: UNT Libraries Government Documents Department

High-field penning-malmberg trap: confinement properties and use in positron accumulation

Description: This dissertation reports on the development of the 60 kG cryogenic positron trap at Lawrence Livermore National Laboratory, and compares the trap`s confinement properties with other nonneutral plasma devices. The device is designed for the accumulation of up to 2{times}10{sup 9} positrons from a linear-accelerator source. This positron plasma could then be used in Bhabha scattering experiments. Initial efforts at time-of-flight accumulation of positrons from the accelerator show rapid ({approximately}100 ms) deconfinement, inconsistent with the long electron lifetimes. Several possible deconfinement mechanisms have been explored, including annihilation on residual gas, injection heating, rf noise from the accelerator, magnet field curvature, and stray fields. Detailed studies of electron confinement demonstrate that the empirical scaling law used to design the trap cannot be extrapolated into the parameter regime of this device. Several possible methods for overcoming these limitations are presented.
Date: September 1, 1997
Creator: Hartley, J.H.
Partner: UNT Libraries Government Documents Department

Enigmatic electrons, photons, and ``empty`` waves

Description: A spectroscopic analysis is made of electrons and photons from the standpoint of physical realism. In this conceptual framework, moving particles are portrayed as localized entities which are surrounded by ``empty`` waves. A spectroscopic model for the electron Stands as a guide for a somewhat similar, but in essential respects radically different, model for the photon. This leads in turn to a model for the ``zeron``. the quantum of the empty wave. The properties of these quanta mandate new basis states, and hence an extension of our customary framework for dealing with them. The zeron wave field of a photon differs in one important respect from the standard formalism for an electromagnetic wave. The vacuum state emerges as more than just a passive bystander. Its polarization properties provide wave stabilization, particle probability distributions, and orbit quantization. Questions with regard to special relativity are discussed.
Date: August 22, 1995
Creator: MacGregor, M.H.
Partner: UNT Libraries Government Documents Department

{mu}{sup +} {yields} e{sup +}{gamma} and related rare decays

Description: The connection of rare decays to supersymmetric grand unification is highlighted, and a brief review of the status of rare decay experiments is given. The status of the MEGA experiment, a search for {mu}{sup +} {yields} e{sup +}{gamma}, is reported. Some ideas for a new experimental arrangement that has the potential to reach a sensitivity of 10{sup {minus}14} are presented.
Date: February 1, 1997
Creator: Cooper, M.D.
Partner: UNT Libraries Government Documents Department

Low mass SN Ia and the late light curve

Description: The late bolometric light curves of type Ia supernovae, when measured accurately over several years, show an exponential decay with a 56d half-life over a drop in luminosity of 8 magnitudes (10 half-lives). The late-time light curve is thought to be governed by the decay of Co{sup 56}, whose 77d half-life must then be modified to account for the observed decay time. Two mechanisms, both relying upon the positron fraction of the Co{sup 56} decay, have been proposed to explain this modification. One explanation requires a large amount of emission at infra-red wavelengths where it would not be detected. The other explanation has proposed a progressive transparency or leakage of the high energy positrons (Colgate, Petschek and Kriese, 1980). For the positrons to leak out of the expanding nebula at the required rate necessary to produce the modified 56d exponential, the mass of the ejecta from a one foe (10{sup 51} erg in kinetic energy) explosion must be small, M{sub ejec} = 0.4M{sub {circle_dot}} with M{sub ejec} {proportional_to} KE{sup 0.5}. Thus, in this leakage explanation, any reasonable estimate of the total energy of the explosion requires that the ejected mass be very much less than the Chandrasekhar mass of 1.4M{sub {circle_dot}}. This is very difficult to explain with the ``canonical`` Chandrasekhar-mass thermonuclear explosion that disintegrates the original white dwarf star. This result leads us to pursue alternate mechanisms of type Ia supernovae. These mechanisms include sub-Chandrasekhar thermonuclear explosions and the accretion induced collapse of Chandrasekhar mass white dwarfs. We will summarize the advantages and disadvantages of both mechanisms with considerable detail spent on our new accretion induced collapse simulations. These mechanisms lead to lower Ni{sup 56} production and hence result in type Ia supernovae with luminosities decreased down to {approximately} 50% that predicted by the ``standard`` model.
Date: December 1995
Creator: Colgate, S. A.; Fryer, C. L. & Hand, K. P.
Partner: UNT Libraries Government Documents Department

A study of the decay {mu} {yields} e{gamma} by the MEGA experiment

Description: The MEGA experiment is designed to search for the lepton-flavor number non-conserving rare decay {mu} {yields} {ital e}{gamma}. Data- taking is complete, with 450 million events on tape taken over approximately 10{sup 7} seconds. A small portion of the data sample has been processed through the complete event reconstruction codes to search for the {mu} {yields} {ital e}{gamma} process. No evidence for the {mu} {yields} {ital e}{gamma} decay is observed at a sensitivity of {approximately}7 x 10{sup -11} (90% confidence).
Date: December 31, 1996
Creator: Hogan, G.E.; Amann, J.F. & Ahmed, M.
Partner: UNT Libraries Government Documents Department

Comments on the possible use of the SLC as an e{sup -}e{sup -} collider

Description: It has been suggested that the SLAC Linear Collider, which was designed to collide electrons with positrons, could be modified to collide electrons with electrons. A cursory examination of this suggestion leads us to conclude that such a modification is technically feasible, but by no means trivial. In this letter we outline the issues that must be addressed to realize this possibility.
Date: February 1, 1996
Creator: Erickson, R.
Partner: UNT Libraries Government Documents Department

A Sampled Master Oscillator for the PEP-II B Factory

Description: A sampled phase-locked loop synchronizes the PEP-II B Factory rings to their SLAC Linac injector. The injection of both electrons and positrons into the separate rings and into their proper rf buckets requires phase shifting the linac rf with respect to the PEP rings. One of every three machine cycles provides the PEP ring an undisturbed reference while the other two thirds of the time the reference is unusable due to the injection scheme. The ring rf must be tunable about its nominal frequency for machine physics use. A sampled phase-locked loop handles the task of synchronizing the PEP-II rf to the linac while maintaining good phase noise. The input reference is sampled at 120 Hz and provides a ring rf signal with less than 0.1{degree} of rms phase jitter at 476 MHz.
Date: May 18, 1999
Partner: UNT Libraries Government Documents Department