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The Value of Nu for Fission of U²³³ by 14 Mev Neutrons as Derived from Charge Distribution Measurements

Description: Abstract: "The charge distribution for fragments from fission of U-235 induced by 14 Mev neutrons, as given by Ford, has been examined to obtain the average number of neutrons per fission. On the basis of some assumptions which seem reasonable a value NU-5.2 +/- 0.5 is obtained. Some evidence is also given which points toward the validity of the Glendenin hypothesis of charge distribution as opposed to that of Present."
Date: 1958
Creator: Wahl, John S.
Partner: UNT Libraries Government Documents Department

Phase coexistence in multifragmentation?

Description: The charge (Z) distributions from intermediate energy heavy-ion reactions depend upon the multiplicity {eta} of intermediate mass fragments through a factor of the form e{sup {minus}cnZ}. Experimentally c starts from zero at low values of the transverse energy E{sub t} and reaches a saturation value at high E{sub t}. In a liquid-gas phase diagram, c = 0 for the saturated vapor, while c {gt} 0 for the unsaturated vapor. It is suggested that in the c {approx} 0 regime the source evaporates down to a sizable remnant, while for c {gt} 0 the source vaporizes completely. Percolation of a finite system portrays a behavior similar to that observed experimentally.
Date: April 1, 1995
Creator: Moretto, L.G.; Phair, L. & Ghetti, R.
Partner: UNT Libraries Government Documents Department

Visualization of Charge Distribution in a Lithium Battery Electrode

Description: We describe a method for direct determination and visualization of the distribution of charge in a composite electrode. Using synchrotron X-ray microdiffraction, state-of-charge profiles in-plane and normal to the current collector were measured. In electrodes charged at high rate, the signatures of nonuniform current distribution were evident. The portion of a prismatic cell electrode closest to the current collector tab had the highest state of charge due to electronic resistance in the composite electrode and supporting foil. In a coin cell electrode, the active material at the electrode surface was more fully charged than that close to the current collector because the limiting factor in this case is ion conduction in the electrolyte contained within the porous electrode.
Date: July 2, 2010
Creator: Liu, Jun; Kunz, Martin; Chen, Kai; Tamura, Nobumichi & Richardson, Thomas J.
Partner: UNT Libraries Government Documents Department

Compact Analytic Expression for the Electric Field of a 2DElliptical Charge Distribution Inside a Perfectly Conducting CircularCylinder

Description: By combining the method of images with calculus of complex variables, we provide a simple expression for the electric field of a two-dimensional (2D) static elliptical charge distribution inside a perfectly conducting cylinder. The charge distribution need not be concentric with the cylinder.
Date: May 29, 2007
Creator: Furman, M.A.
Partner: UNT Libraries Government Documents Department

Coherent Beam-Beam Interactions in Electron-Positron Colliders

Description: We present the results of a new calculational technique that evaluates the beam-beam force due to an arbitrary charge distribution. We find coherent instabilities that dominate at certain operating points and depend strongly on the degree of damping in the system. We conclude that while these resonances may play a significant role for colliders with low damping, with a careful choice of operating points they should present no danger to the new generation of high luminosity heavy-quark factories under design.
Date: August 1, 1991
Creator: Krishnagopal, S.
Partner: UNT Libraries Government Documents Department

Do phase transitions survive binomial reducibility and thermal scaling?

Description: First order phase transitions are described in terms of the microcanonical and canonical ensemble, with special attention to finite size effects. Difficulties in interpreting a `caloric curve` are discussed. A robust parameter indicating phase coexistence (univariance) or single phase (bivariance) is extracted for charge distributions. 9 refs., 4 figs.
Date: May 1, 1996
Creator: Moretto, L.G.; Phair, L. & Wozniak, G.J.
Partner: UNT Libraries Government Documents Department


Description: Emittance compensation is a well established technique for minimizing the emittance of an electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincide the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating game. We describe a method and tools for a compensation that includes the beam magnetization.
Date: June 25, 2007
Creator: KEWISCH,J. & CHANG, X.
Partner: UNT Libraries Government Documents Department


Description: Transverse wakefield effects in the high-gradient accelerating structure of the Two-Beam Accelerator (TBA) [1-3] are analyzed theoretically using three different models. The first is a very simple two-particle model due to Wilson [4]; the second, due to Chao, Richter, and Yao [5], is for a beam with uniform charge distribution, constant betatron wavelength, and a linear wake approximation. Both of these models give analytic scaling laws. The third model has a Gaussian beam (represented by 11 superparticles), energy variation across the bunch, acceleration, variation of betatron focusing with energy, and variation of the wakefield from linearity. The three models are compared, and the third model is used to explore the wakefield effects when accelerator parameters such as energy, energy spread, injection energy, accelerating gradient, and betatron wavelength are varied. Also explored are the sensitivity of the beam to the wakefield profile and to the longitudinal charge distribution. Finally, in consideration of wakefield effects, possible parameters of a TBA are presented.
Date: August 1, 1985
Creator: Selph, F. & Sessler, A.
Partner: UNT Libraries Government Documents Department

Modeling of the phase evolution in Mg1-xAlxB2 (0<x<0.5) and its experimental signatures

Description: Despite the chemical and structural simplicity of MgB{sub 2}, at 39 K this compound has the highest known {Tc} of any binary compound. Electron doping by substituting Al for Mg leads to decreasing Tc and the observed concentration dependent rate of decrease has been proposed to arise from the non-ideal character of MgB{sub 2}-AIB{sub 2} solid solutions, which derives from the existence of an ordered Mg{sub 0.5}Al{sub 0.5}B{sub 2} compound. Heterogeneous nano-scale structure patterns in solid solutions have emerged as an important concept for complex materials, ranging from actinide alloys and oxides to high-temperature cuprate superconductors and mallganite-based materials exhibiting colossal magnetoresistivity. In this work we investigate the formation of structural heterogeneities in Mg{sub 1-x}AI{sub x}B{sub 2}, which take the form of nano-scale AI-AI and AI-Mg domains of different geometry and size, using molecular statics/dynamics simulations and in particular we study the corresponding signatures in diffraction experiments. In order to undertake this task we first derive appropriate Mg-AI-B semi-empirical potentials within the Modified Embedded Atom Method formalism. These potentials are also applied to explore the equilibrium Mg{sub 1-x}AI{sub x}B{sub 2} phase diagram for 0 &lt; x &lt; 0.5. Additionally, density functional theory calculations were utilized to study the influence of heterogeneities on the electronic structure and charge distribution in Mg{sub 1-x}AI{sub x}B{sub 2}.
Date: January 1, 2009
Creator: Andersson, Anders David; Casillas, Luis; Lezama Pacheco, Juan & Conradson, Steven D
Partner: UNT Libraries Government Documents Department

High-density nanopore array for selective biomolecule transport.

Description: Development of sophisticated tools capable of manipulating molecules at their own length scale enables new methods for chemical synthesis and detection. Although nanoscale devices have been developed to perform individual tasks, little work has been done on developing a truly scalable platform: a system that combines multiple components for sequential processing, as well as simultaneously processing and identifying the millions of potential species that may be present in a biological sample. The development of a scalable micro-nanofluidic device is limited in part by the ability to combine different materials (polymers, metals, semiconductors) onto a single chip, and the challenges with locally controlling the chemical, electrical, and mechanical properties within a micro or nanochannel. We have developed a unique construct known as a molecular gate: a multilayered polymer based device that combines microscale fluid channels with nanofluidic interconnects. Molecular gates have been demonstrated to selectively transport molecules between channels based on size or charge. In order to fully utilize these structures, we need to develop methods to actively control transport and identify species inside a nanopore. While previous work has been limited to creating electrical connections off-channel or metallizing the entire nanopore wall, we now have the ability to create multiple, separate conductive connections at the interior surface of a nanopore. These interior electrodes will be used for direct sensing of biological molecules, probing the electrical potential and charge distribution at the surface, and to actively turn on and off electrically driven transport of molecules through nanopores.
Date: November 1, 2011
Creator: Patel, Kamlesh D.
Partner: UNT Libraries Government Documents Department

Longitudinal electron bunch diagnostics using coherent transition radiation

Description: The longitudinal charge distribution of electron bunches in the Fermilab/Nicadd A0 photoinjector was determined using the coherent transition radiation produced by electrons passing through a thin metallic foil. The autocorrelation of the transition radiation signal was measured with a Michelson-type interferometer. The response function of the interferometer was determined from measured and simulated power spectra for low electron bunch charge and maximum longitudinal compression. A Kramers-Kronig technique was used to determine longitudinal charge distribution. Measurements were performed for electron bunch lengths in the range from 0.3 to 2 ps (rms).
Date: May 1, 2005
Creator: Mihalcea, D.; Bohn, C.L.; U., /Northern Illinois; Happek, U.; U., /Georgia; Piot, P. et al.
Partner: UNT Libraries Government Documents Department

Effects of transverse beam size in beam position monitors.

Description: The fields produced by a long beam with a given transverse charge distribution in a homogeneous vacuum chamber are studied. Signals induced by the displaced finite-size beam on electrodes of a beam position monitor (BPM) are calculated and compared to those from a pencil beam. The non-linearities and corrections to BPM signals due to a finite transverse beam size are calculated for an arbitrary chamber cross section. Simple analytical expressions are given for a few particular transverse distributions of the beam current in a circular or rectangular chamber. Of particular interest is a general proof that in an arbitrary homogeneous chamber the beam-size corrections vanish for any axisymmetric beam current distribution.
Date: January 1, 2001
Creator: Kurennoy, S. (Sergey)
Partner: UNT Libraries Government Documents Department

ECR-based atomic collision physics research at ORNL

Description: After a brief summary of the present capability and configuration of the ORNL Multicharged Ion Research Facility (MIRF), and of upcoming upgrades and expansions, the presently on-line atomic collisions experiments are described. In the process, the utility of intense, cw ion beams extracted from ECR ion sources for low-signal rate experiments is illustrated.
Date: April 1997
Creator: Meyer, F. W.; Bannister, M. E.; Hale, J. W. & Havener, C. C.
Partner: UNT Libraries Government Documents Department

Interpreting multiplicity-gated fragment distributions from heavy-ion collisions

Description: In recent years, multifragmentation of nuclear systems has been extensively studied, and many efforts have been made to clarify the underlying physics. However, no clear consensus exists on the mechanism for multifragmentation. Is the emission of intermediate mass fragments (IMF: 3 {le} Z {le} 20) a dynamical process (brought on by the occurrence of instabilities of one form or another) or a statistical process (i.e. the decay probabilities are proportional to a suitably defined exit channel phase space)? Historically the charge (mass) distribution has played and still plays a very important role in characterizing multifragmentation. Since this subject`s inception, the near power-law shape of the charge and mass distributions was considered an indication of criticality for the hot nuclear fluid produced in light ion and heavy ion collisions. Here, the authors have studied different aspects of the charge distributions. The implications of the experimental evidence presented here are potentially far reaching. On the one hand, the thermal features observed in the n-fragment emission probabilities for the {sup 36}Ar + {sup 197}Au reaction extend consistently to the charge distributions and strengthen the hypothesis of the important role of phase space in describing multifragmentation. On the other hand, they have investigated charge correlation functions of multi-fragment decays to search for the enhanced production of nearly equal-sized fragments predicted in several theoretical works.
Date: February 1, 1997
Creator: Phair, L.; Moretto, L.G.; Rubehn, T.; Wozniak, G.J.; Beaulieu, L.; Tso, K. et al.
Partner: UNT Libraries Government Documents Department

The Brookhaven muon g-2 experiment

Description: A new experiment is being mounted at BNL to measure the anomalous magnet moment of the muon to 3 parts in 10{sup 7}. In this talk I will describe the physics issues that this precision allows us to explore, the experimental method, and an interesting new device which we will use to inject muons into our muon storage ring. The device is a 1.45T non-ferrous superconducting magnet, where all fringe field is contained by a superconducting sheet.
Date: March 1, 1995
Creator: Bunce, G.
Partner: UNT Libraries Government Documents Department

Emittance growth and halo formation in a low energy proton beam

Description: We have measured emittances in a low-energy proton beam at energies between 19 and 45 KeV and currents between 9 and 39 mA. The rms emittance of the space-charge dominated proton beam, as measured by a moving-slit emittance probe, grew by an average amount of 60% in a propagation distance of 2.5 cm. An Abel inversion procedure was applied to the measured transverse charge distribution of the proton beam in order to calculate the electrostatic field energy, which is the driving quantity for emittance growth. We have found that all of the emittance growth is due to a halo containing {approx_equal} 10% of the beam particles.
Date: April 1, 1993
Creator: Palkovic, J.
Partner: UNT Libraries Government Documents Department

Sensitivity of the CSR Self-Interaction to the Local Longitudinal Charge Concentration of an Electron Bunch

Description: Recent measurements of the coherent synchrotron radiation (CSR) effect carried out at CERN and at Jefferson Lab indicate that the observed emittance growth and energy modulation due to the orbit-curvature-induced bunch self-interaction are sometimes bigger than the results predicted from previous analyses and simulations based on a Gaussian longitudinal charge distribution. In this paper, by performing a model study, we show both analytically and numerically that when the longitudinal bunch charge distribution involves concentration of charges in a small fraction of the bunch length, enhancement of the CSR self-interaction beyond the Gaussian prediction may occur.
Date: August 1, 2000
Creator: Li, R.
Partner: UNT Libraries Government Documents Department

Unusual layer-dependent charge distribution, collective mode coupling, and superconductivity in multilayer cuprate Ba2Ca3Cu4O8F2

Description: Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high Tc superconductor Ba2Ca3Cu4O8F2 (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO2 layers, respectively. For the states originating from two inequivalent CuO2 layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.
Date: January 22, 2009
Creator: Chen, Yulin; Iyo, Akira; Yang, Wanli; Ino, Akihiro; Arita, M.; Johnston, Steve et al.
Partner: UNT Libraries Government Documents Department


Description: An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RMIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 {mu}. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch.
Date: June 25, 2007
Creator: KEWISCH,J. & CHANG, X.
Partner: UNT Libraries Government Documents Department

Final mechanical design, fabrication, and commissioning of a wire scanner and scraper assembly for halo-formation measurements in a proton beam

Description: The 6.7 MeV, 100 mA proton beam being produced in the Low Energy Demonstration Accelerator (LEDA) RFQ is being injected into a 52 magnet lattice in order to study the charged-beam phenomenon known as beam halo [1]. Quadrupole magnets in the lattice are purposely mismatched to cause or amplify halo formation in the beam. Interceptive diagnostics that consist of a thin wire and a paddle type device called a scraper are placed in the beam to obtain charge-distribution data. The charge-distribution data is used to create a current-density distribution plot of the beam at the probed location [2]. This paper describes the mechanical design, fabrication, and commissioning of the interceptive diagnostic devices and the assembly that carries them.
Date: April 1, 2001
Creator: Valdiviez, R. (Robert); Martinez, F. A. (Felix A.); Rendon, Armando M.; Wright, T. O. (Tony O.); Ledford, J. E. (John E.); Patterson, N. K. (Norman K.) et al.
Partner: UNT Libraries Government Documents Department

Longitudinal Bunch Shape Diagnostics With Coherent Radiation And a Transverse Deflecting Cavity at TTF2

Description: At the DESY TTF2 linear accelerator three special techniques to characterize the longitudinal charge distribution of the electron bunches that drive the free-electron laser are currently under study: electro-optical sampling, far-infrared spectral analysis of coherent radiation and the use of a transverse deflecting cavity to streak the bunch. The principles and implementations of the latter two are described in this paper. Details on electro-optical sampling can be found in [1].
Date: August 4, 2005
Creator: Grimm, O.; Frohlich, L.; Klose, K.; Nagl, M.; Peters, O.; Rossbach, J. et al.
Partner: UNT Libraries Government Documents Department

A Density Functional Approach to Polarizable Models: A Kim-Gordon-Response Density Interaction Potential for Molecular Simulations

Description: A combined linear response--frozen electron density model has been implemented in a molecular dynamics scheme derived from an extended Lagrangian formalism. This approach is based on a partition of the electronic charge distribution into a frozen region described by Kim-Gordon theory, and a response contribution determined by the instaneous ionic configuration of the system. The method is free from empirical pair-potentials and the parameterization protocol involves only calculations on properly chosen subsystems. They apply this method to a series of alkali halides in different physical phases and are able to reproduce experimental structural and thermodynamic properties with an accuracy comparable to Kohn-Sham density functional calculations.
Date: April 7, 2005
Creator: Tabacchi, G; Hutter, J & Mundy, C
Partner: UNT Libraries Government Documents Department