738 Matching Results

Search Results

Advanced search parameters have been applied.

Raman study of ``boson peak`` in ion-implanted GaAs: Dependence on ion dose and dose rate

Description: Findings on the amorphization of GaAs were interpreted in the fractal model and correlated with recent analysis of ion-induced damage from Raman and ion channeling data. The Raman spectra were decomposed on phonon-fracton cruve and Gaussian bands by fitting. Crossover frequency {omega}{sub col} between phonon and fracton regimes and the fractal exponent ({sigma}+d-D){tilde d}/D shows a pronounced dependence on applied ion dose and weak dependence on dose rate. Evolution of the fractal component is compared with ion channeling and Raman spectra of phonon bands. The fractal component is strongly dependent on ion dose and is the amorphous component and is weakly dependent on dose rate. It indicates that the fractal component is not connected with point crystalline defects, to which ion channeling is particularly sensitive. The fractal correlation length {xi} and spectral dimension d, calculated from crossover frequency and fractal exponent, changes from {xi}=6A and {tilde d}=0.2 for weakly damaged samples to {xi}=10A and {tilde d}=0.8 for completely amorphized samples.
Date: November 1, 1993
Creator: Ivanda, M.; Desnica, U.V. & Haynes, T.E.
Partner: UNT Libraries Government Documents Department

Alpha and gamma radiation effects on air-water systems at high gas/liquid ratios

Description: Radiolysis tests were conducted on air-water systems to examine the effects of radiation on liquid phase chemistry under high gas/liquid volume (G/L) ratios that are characteristic of an unsaturated nuclear waste repository setting. Test parameters included temperatures of 25, 90, and 200{degrees}C; gamma vs. alpha radiation; dose rates of {approximately}3500 and 50,000 rad/h; and G/L ratios of 10 and 100. Formate, oxalate, and total organic carbon contents increased during irradiation of the air-water systems in gamma and alpha tests at low-dose rate ({approximately}3500 rad/h). Increases in organic components were not observed for tests run at 200{degrees}C or high-dose rates (50,000 rad/h). In the tests where increases in organics occurred, the formate and oxalate were preferentially enriched in solutions that were rinsed from the test vessel walls. Nitrate (NO{sub 3}{sup {minus}}) is the dominant anion produced during the radiolysis reactions. Significant nitrite (NO{sub 2}{sup {minus}}) also occurs in some high-dose rate tests, with the reduced form of nitrogen possibly resulting from reactions with the test vessels. These results indicate that nitrogen acids are being produced and concentrated in the limited quantities of solution present in the tests. Nitrate + nitrite production varied inversely with temperature, with the lowest quantities being detected for the higher temperature tests. The G(NO{sub 3}{sup {minus}} + NO{sub 2}{sup {minus}}) values for the 25, 90, and 200{degrees}C experiments with gamma radiation are 3.2 {+-} 0.7, 1.3 {+-} 1.0, and 0.4 {+-} 0.3, respectively. Thus, the elevated temperatures expected early in the life of a repository may counteract pH decreases resulting from nitrogen acid production. Little variation was observed in G values as a function of dose rate or gas/liquid ratio.
Date: August 1, 1993
Creator: Wronkiewicz, D.J. & Bates, J.K.
Partner: UNT Libraries Government Documents Department

Review of scientific and technical options for the Superconducting Super Collider Program

Description: This document is a review of options for the Superconducting Super Collider (SSC) Program. It is the result of an informal study by an ad-hoc working group consisting of Laboratory physicists and engineers who investigated the physics and technical implications of a number of possible alternative SSC programs. Previous studies have shown, and early in this study it was confirmed, that a collider of approximately 20 TeV protons on 20 TeV protons with a luminosity of 10{sup 33} cm{sup {minus}2}s{sup {minus}1} at each interaction region is needed to support a physics program that is guaranteed to answer existing particle physics questions and make new discoveries. Therefore, all options considered in this document were consistent with attainment of these original goals for the SSC. One promising option considered was a program of colliding anti-protons on protons as a possible means to reduce the cost of the SSC by eliminating one of the Collider rings. However, the luminosity requirements to obtain the SSC physics goals remains the same as for protons colliding with protons and this study confirms that even though progress has been made over the last ten years in obtaining the high intensity anti-proton beams necessary, a luminosity higher than 10{sup 32} cannot be guaranteed. Other options were examined to see what advantages could be derived by departing from the SSC baseline program, either in schedule, in parameters, by staging, or by combinations of these options. Even though we considered re-examination of the cost of the baseline program to be beyond the scope of this document, differential cost savings were estimated. Finally, a brief survey of progress over the last ten years in various technical areas that might lead to more cost effective engineering designs was included in this study, such as higher magnetic field magnets resulting from lower operating ...
Date: November 1, 1993
Creator: Dombeck, T.
Partner: UNT Libraries Government Documents Department

High p{sub t} physics processes

Description: In order to estimate the ``physics reach`` of various pp or {bar p}p colliders, several physics processes of interest have been studied. For each process, the number of produced events required to carry out meaningful.physics studies or detect statistically significant signals has been estimated. These estimates are largely based on detailed studies for the SDC and GEM design reports. Extrapolation to other energies takes into account calculated cross sections and crude background estimates. To convert the required number of events into an average luminosity to be delivered by the machine, a ``running year`` of 10{sup 7} seconds is used. This time is consistent with SSC design plans, which call for an 80% detector up time and enough stable beam time to result in 10{sup 7} ``live`` seconds per operating year. Note that when making comparisons with existing facilities, any deviation from these assumptions should be taken into account. The conclusions of this study are generally sim-ilar to those reached by Eichten, et al. in 1984 and by the Drell Panel in 1990.
Date: October 1, 1993
Creator: Bird, F.; Blocker, C.; Fukui, T.; McBride, P.; Paige, F.; Pal, T. et al.
Partner: UNT Libraries Government Documents Department

A Review of Irradiation Effects on Organic-Matrix Insulation

Description: This review assesses the data base on epoxy and polyimide matrix insulation to determine whether organic electric insulation systems can be used in the toroidal field (TF) magnets of next generation fusion devices such as ITER* and TPX*. Owing to the difficulties of testing insulation under fusion reactor conditions, there is a considerable mismatch between the ITER requirements and the data that are currently available. For example, nearly all of the high-dose (5 x 10{sup 7} to 10{sup 8} Gy) data obtained on epoxy and polyimide matrix insulation employed gamma irradiation, electron irradiation, or reactor irradiation with a fast neutron fluence far below 10{sup 23}/m{sup 2}, the fluence expected for the insulation at the TF magnets, as set forth in ITER conceptual design documents. Also, the neutron spectrum did not contain a very high energy (E {ge} 5 MeV) component. Such data underestimate the actual damage that would be obtained with the neutron fluence and spectrum expected at a TF magnet. Experiments on a polyimide (Kapton) indicate that gamma or electron doses or mixed gamma and neutron reactor doses would have to be downgraded by a factor of up to ten to simulate fusion neutron doses. Even when neutrons did constitute a significant portion of the total dose, B-containing E-glass reinforcement was often used; therefore, excess damage from the {sup 10}B + n {yields} {sup 7}Li + {alpha} reaction occurred near the glass-epoxy interface. This problem can easily be avoided by substituting B-free glass (R, S, or T types).
Date: June 1, 1993
Creator: Simon, N.J.
Partner: UNT Libraries Government Documents Department

The magnitude of the gluon condensate and the masses of c and b quarks from the families of T/{Psi} and {Upsilon} mesons

Description: It is shown that the model used by Shifman, Vainshtein, and Zakharov for the description of the experimental function R{sub c}(s) in the form of a sum of {delta}-functions and the plateau contradicts the Wilson operator expansion (O.E.) in the terms due to the gluon condensate. A QCD model with an infinite number of vector mesons does satisfy the requirements of the O.E. for masses and electronic width resonances close to the experimental values. The region of allowable values of the masses of c- and b-quarks and the gluon condensate compatible with the O.E. is obtained.
Date: November 1, 1993
Creator: Geshkenbein, B. & Morgunov, V.
Partner: UNT Libraries Government Documents Department

QCD sum rules and Compton scattering

Description: The authors extend QCD sum rule analysis to moderate energy fixed angle Compton scattering. In this kinematic region there is a strong similarity to the sum rule treatment of electromagnetic form factors, although the four-point amplitude requires a modification of the Borel transform. To illustrate their method, they derive the sum rules for helicity amplitudes in pion Compton scattering and estimate their large-t behavior in the local duality approximation.
Date: January 1, 1993
Creator: Coriano, Claudio; Radyushkin, Anatoly & Sternman, George
Partner: UNT Libraries Government Documents Department

Exploiting the single-lepton event structure in the search for the top quark

Description: We discuss whether the event structure can be useful in searching for the top quark in the single-lepton channel at the Tevatron, where the main obstacle is a considerable background from QCD W+ multijet production. We restrict our discussion to the case of a Standard Model top quark of heavy mass, M{sub top}>100 GeV.
Date: June 1, 1993
Creator: Cobal, M.; Leone, S. & Grassman, H.
Partner: UNT Libraries Government Documents Department

Yukawa unification: The good, the bad, and the ugly

Description: We analyze some consequences of grand unification of the third-generation Yukawa couplings, in the context of the minimal supersymmetric standard model. We address two issues: the prediction of the top quark mass, and the generation of the top-bottom mass hierarchy through a hierarchy of Higgs vacuum expectation values. The top mass is strongly dependent on a certain ratio of superpartner masses. And the VEV hierarchy always entails some tuning of the GUT-scale parameters. We study the RG equations and their semi-analytic solutions, which exhibit several interesting features, such as a focusing effect for a large Yukawa coupling in the limit of certain symmetries and a correlation between the A terms (which contribute to b {yields} s{gamma}) and the gaugino masses. This study shows that non-universal soft-SUSY-breaking masses are favored (in particular for splitting the Higgs-doublets via D-terms and for allowing more natural scenarios of symmetry breaking), and hints at features desired in Yukawa-unified models. Several phenomenological implications are also revealed.
Date: May 1993
Creator: Rattazzi, R.; Sarid, U. & Hall, L. J.
Partner: UNT Libraries Government Documents Department

Probing nucleon strangeness with parity violating electron scattering

Description: The electromagnetic and weak neutral currents display different sensitivities to various strange quark matrix elements of the nucleon. Measurements of the parity-violating electron-proton and electron-nucleus asymmetries at intermediate energies could allow one to extract limits on the nucleon's strange-quark form factors. The prospects for deriving such constraints from present and approved experiments at MIT-Bates and CEBAF, as well as the implications of such measurements for models of nucleon strangeness, are discussed.
Date: June 1, 1993
Creator: Musolf, M.
Partner: UNT Libraries Government Documents Department

Infrared fixed point solution for the top quark mass and unification of couplings in the MSSM

Description: We analyze the implications of the infrared quasi fixed point solution for the top quark mass in the Minimal Supersymmetric Standard Model. This solution could explain in a natural way the relatively large value of the top quark mass and, if confirmed experimentally, may be suggestive of the onset of nonperturbative physics at very high energy scales. In the framework of grand unification, the expected bottom quark -- tau lepton Yukawa coupling unification is very sensitive to the fixed point structure of the top quark mass. For the presently allowed values of the electroweak parameters and the bottom quark mass, the Yukawa coupling unification implies that the top quark mass must be within ten percent of its fixed point values.
Date: August 1, 1993
Creator: Bardeen, W.A.; Carena, M.; Pokorski, S. & Wagner, C.E.M.
Partner: UNT Libraries Government Documents Department

Assessment of the Available (Sup 233)U Cross Sections Evaluations in the Calculation of Critical Benchmark Experiments

Description: In this report we investigate the adequacy of the available {sup 233}U cross-section data for calculation of experimental critical systems. The {sup 233}U evaluations provided in two evaluated nuclear data libraries, the U. S. Data Bank [ENDF/B (Evaluated Nuclear Data Files)] and the Japanese Data Bank [JENDL (Japanese Evaluated Nuclear Data Library)] are examined. Calculations were performed for six thermal and ten fast experimental critical systems using the Sn transport XSDRNPM code. To verify the performance of the {sup 233}U cross-section data for nuclear criticality safety application in which the neutron energy spectrum is predominantly in the epithermal energy range, calculations of four numerical benchmark systems with energy spectra in the intermediate energy range were done. These calculations serve only as an indication of the difference in calculated results that may be expected when the two {sup 233}U cross-section evaluations are used for problems with neutron spectra in the intermediate energy range. Additionally, comparisons of experimental and calculated central fission rate ratios were also made. The study has suggested that an ad hoc {sup 233}U evaluation based on the JENDL library provides better overall results for both fast and thermal experimental critical systems.
Date: January 1, 1993
Creator: Leal, L.C.
Partner: UNT Libraries Government Documents Department

Tau physics

Description: This report discusses the following topics: [tau] production and related [tau] properties; general discussion of [tau] decays; leptonic decays; hadronic decays; the [tau] in atomic physics; and the [tau] neutrino: [nu][sub [tau]]
Date: March 1, 1993
Creator: Perl, M.L.
Partner: UNT Libraries Government Documents Department

RESRAD update

Description: A microcomputer program called RESRAD, which implements a pathway analysis method for radiological risk assessment, was developed by Argonne National Laboratory (ANL) in 1989. This program is used to derive allowable residual concentrations of radionuclides in soil and to predict effective dose equivalents and excess cancer incidence risks incurred by an individual exposed to radioactive materials. Since its development, the RESRAD code has been adopted by DOE in Order 5400.5 for the derivation of soil cleanup criteria and dose calculations, and it has been used widely by DOE, other agencies, and their contractors. The original models used by ANL to develop RESRAD were initially developed as part of a DOE effort that began in the early 1980s and involved most of the national laboratories and DOE program offices. The RESRAD code is continuously improved and updated to incorporate comments from users and new features that ease the interaction with users and increase the code's capability and flexibility. The DOE Offices of Environmental Guidance and Environmental Restoration also provide periodic guidance regarding any significant changes to the code. The RESRAD update, Version 5.0, has substantial improvements in many aspects compared with the last version released in 1989.
Date: January 1, 1993
Creator: Yu, C.; Cheng, J.J.; Zielen, A.J.; Jones, L.G.; LePoire, D.J.; Wang, Y.Y. (Argonne National Lab., IL (United States)) et al.
Partner: UNT Libraries Government Documents Department

Investigation of ion beam mixing of iron marker layers in aluminum oxide by RBS

Description: Thin films made with a thin embedded marker layer of iron or iron oxide in amorphous alumina were ion mixed with 210 key Ar over a temperature range of RT to 750[degrees]C in vacuum. The dose range was 5[times]10[sup 15]-7[times]10[sup 16]ions/cm[sup 2] with an average dose rate of 4.5[times]10[sup 12]ionS/cm[sup 2]-sec. The resulting marker distributions were analyzed using RBS. Spreading of the iron RBS peak due to mixing into the alumina matrix was observed in the Fe[sub 2]O[sub 3] marker samples and was clearly seen to be a function of temperature (>400[degrees]C) and dose, whereas for the Fe marker sample, no such temperature dependence was observed. An activation energy for the thermally assisted ion mixing in the Fe[sub 2]O[sub 3] marker sample was determined to be 0.69 eV in comparison to an activation energy of 1.77 eV for samples that underwent only a thermal treatment.
Date: January 1, 1993
Creator: Cooper, E.A.; Nastasi, M. & Sickafus, K.E.
Partner: UNT Libraries Government Documents Department

[Research programs from the University of South Carolina on High Energy Physics]. [119 Technical Progress Report]

Description: Work on three main experiments is summarized: (1) study of charm physics in a wide-band photon beam; (2) charmless two-body decays of b-flavored mesons and baryons studied with a ring imaging Cherenkov counter; and (3) the AMY Program, which studies e[sup +]e[sup [minus]] interactions using the TRISTAN collider at KEK, with emphasis on trigger upgrades. Future work related to the existence of a 17-keV neutrino in [beta] decay and [nu][sub [mu]]/[nu][sub [tau]] oscillation is described.
Date: January 1, 1993
Creator: Rosenfeld, C.
Partner: UNT Libraries Government Documents Department

Investigation of the effects of polyelectrolyte coatings on colloid transport in porous media

Description: Goal is to study the repulsive interaction forces between humic- coated colloids and negatively charged porous media surfaces. Filtration experiments were carried out on hematite coated with humic acid or NOM, in porous media or packed bed (silica bed). Effects of Ca[sup 2+] are being studied. Results so far indicate that many humic coating properties (molecular size, acidity, polarity, surface conformation) have an important effect on colloid attachment rates but very little effect on colloid electrophoretic mobility; steric repulsive forces are proposed to account for these observations. Some humic coatings are more effective in enhancing colloid transport in quartz beds than in enhancing colloid stability. Other effects are discussed.
Date: January 1, 1993
Creator: Olson, T.M.
Partner: UNT Libraries Government Documents Department

Interfacial chemistry in solvent extraction systems

Description: Research this past year continued to emphasize characterization of the physicochemical nature of the microscopic interfaces, i.e., reversed micelles and other association microstructures, which form in both practical and simplified acidic organophosphorus extraction systems associated with Ni, Co, and Na in order to improve on the model for aggregation of metal-extractant complexes. Also, the macroscopic interfacial behavior of model extractant (surfactant) molecules was further investigated. 1 fig.
Date: January 1, 1993
Creator: Neuman, R.D.
Partner: UNT Libraries Government Documents Department

First measurement of the left-right Z cross section asymmetry in polarized e[sup +]e[sup [minus]] collisions at the SLC

Description: The SLAC Linear Collider (SLC) has recently been upgraded to produce, accelerate, and collide a spin polarized electron beam. The average beam polarization during the 1992 run was (22.4 [plus minus] 0.7)%. The SLD Collaboration used the polarized beam to perform the first measurement of the left-right cross section asymmetry (A[sub LR]) for Z boson production by e[sup +]e[sup [minus]] collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with a sample of 10,224 Z decays. The measured value of A[sub LR] is 0.100 [plus minus] 0.044(stat.) [plus minus] O.004(syst.) which determines the effective weak mixing angle to be sin[sup 2][theta][sub W][sup eff] = 0.2378 [plus minus] 0.0056(stat.) [plus minus] 0.0005(syst.).
Date: January 1, 1993
Creator: Swartz, M.L.
Partner: UNT Libraries Government Documents Department

Wetting and dispersion in ceramic/polymer melt injection molding systems

Description: This program had two major areas of emphasis: (1) factors influencing state of particulate dispersion and rheological properties of ceramic powder/polymer melt mixtures, and (2) effect of interfacial bonding strength on mechanical and rheological properties of ceramic particle/polymer composites. Alumina and silica in various polyethylenes were used.
Date: January 1, 1993
Creator: Sacks, M.D. (Florida Univ., Gainesville, FL (United States). Dept. of Materials Science and Engineering) & Williams, J.W. (Florida Univ., Gainesville, FL (United States). Dept. of Materials Science and Engineering 3M Co., St. Paul, MN (United States))
Partner: UNT Libraries Government Documents Department

Laser desorption in an ion trap mass spectrometer

Description: Laser desorption in a ion-trap mass spectrometer shows significant promise for both qualitative and trace analysis. Several aspects of this methodology are discussed in this work. We previously demonstrated the generation of both negative and positive ions by laser desorption directly within a quadrupole ion trap. In the present work, we explore various combinations of d.c., r.f., and time-varying fields in order to optimize laser generated signals. In addition, we report on the application of this method to analyze samples containing compounds such as amines, metal complexes, carbon clusters, and polynuclear aromatic hydrocarbons. In some cases the ability to rapidly switch between positive and negative ion modes provides sufficient specificity to distinguish different compounds of a mixture with a single stage of mass spectrometry. In other experiments, we combined intensity variation studies with tandem mass spectrometry experiments and positive and negative ion detection to further enhance specificity.
Date: January 1, 1993
Creator: Eiden, G.C.; Cisper, M.E.; Alexander, M.L.; Hemberger, P.H. & Nogar, N.S.
Partner: UNT Libraries Government Documents Department

Spectra of Heliumlike Krypton From Tokamak Fusion Test Reactor Plasmas

Description: Krypton has been injected into ohmically-heated TFTR plasmas with peak electron temperatures of 6 key to study the effects of krypton on the plasma performance and to investigate the emitted krypton line radiation, which is of interest for future-generation tokamaks such as ITER, both as a diagnostic of the central ion temperature and for the control of energy release from the plasma by radiative cooling. The emitted radiation was monitored with a bolometer array, an X-ray pulse height analysis system, and a high-resolution Johann-type crystal spectrometer; and it was found to depend very sensitively on the electron temperature profile. Satellite spectra of heliumlike krypton, KrXXXV, near 0.95 [Angstrom] including lithiumlike, berylliumlike and boronlike features were recorded in second order Bragg reflection. Radiative cooling and reduced particle recycling at the plasma edge region were observed as a result of the krypton injection for all investigated discharges. The observations are in reasonable agreement with modeling calculations of the krypton ion charge state distribution including radial transport.
Date: April 1, 1993
Creator: Bitter, M.; Hsuan, H.; Bush, C.; Cohen, S.; Cummings, C.J.; Grek, B. et al.
Partner: UNT Libraries Government Documents Department

Studies of complexity in fluid systems

Description: Objective is to bring together researchers from several disciplines (mathematics, numerical computation, theoretical and experimental physics) who share an interest in the development of complexity in fluid systems. Work is in progress on development of singular interfluid interfaces on several fronts. Striking variations in droplet formation can be observed in physical experiments and simulations based on simple models. High-speed photographs are being taken of small liquid drop breaking into droplets. Experimental studies of granular materials are being continued.
Date: February 1, 1993
Creator: Kadanoff, L.P.; Constantin, P.; Dupont, T.F. & Nagel, S.
Partner: UNT Libraries Government Documents Department