5,675 Matching Results

Search Results

Low-energy vibrations at the InSb(110) surface

Description: Article on low-energy vibrations at the InSb(110) surface along the ΓΥ direction.
Date: December 15, 1995
Creator: Buongiorno Nardelli, Marco; Cvetko, D.; De Renzi, V.; Floreano, L.; Morgante, A.; Peloi, M. et al.
Partner: UNT College of Arts and Sciences

Precision solid liner experiments on Pegasus II

Description: Pulsed power systems have been used in the past to drive solid liner implosions for a variety of applications. In combination with a variety of target configurations, solid liner drivers can be used to compress working fluids, produce shock waves, and study material properties in convergent geometry. The utility of such a driver depends in part on how well-characterized the drive conditions are. This, in part, requires a pulsed power system with a well-characterized current wave form and well understood electrical parameters. At Los Alamos, the authors have developed a capacitively driven, inductive store pulsed power machine, Pegasus, which meets these needs. They have also developed an extensive suite of diagnostics which are capable of characterizing the performance of the system and of the imploding liners. Pegasus consists of a 4.3 MJ capacitor bank, with a capacitance of 850 {micro}f fired with a typical initial bank voltage of 90 kV or less. The bank resistance is about 0.5 m{Omega}, and bank plus power flow channel has a total inductance of about 24 nH. In this paper the authors consider the theory and modeling of the first precision solid liner driver fielded on the LANL Pegasus pulsed power facility.
Date: September 1, 1995
Creator: Bowers, R.L.; Brownell, J.H. & Lee, H.
Partner: UNT Libraries Government Documents Department

Criticality benchmark results for the ENDF60 library with MCNP{trademark}

Description: The continuous-energy neutron data library ENDF60, for use with the Monte Carlo N-Particle radiation transport code MCNP4A, was released in the fall of 1994. The ENDF60 library is comprised of 124 nuclide data files based on the ENDF/B-VI (B-VI) evaluations through Release 2. Fifty-two percent of these B-VI evaluations are translations from ENDF/B-V (B-V). The remaining forty-eight percent are new evaluations which have sometimes changed significantly. Among these changes are greatly increased use of isotopic evaluations, more extensive resonance-parameter evaluations, and energy-angle correlated distributions for secondary particles. In particular, the upper energy limit for the resolved resonance region of {sup 235}U, {sup 238}U and {sup 239}Pu has been extended from 0.082, 4.0, and 0.301 keV to 2..25, 10.0, and 2.5 keV respectively. As regulatory oversight has advanced and performing critical experiments has become more difficult, there has been an increased reliance on computational methods. For the criticality safety community, the performance of the combined transport code and data library is of interest. The purpose of this abstract is to provide benchmarking results to aid the user in determining the best data library for their application.
Date: July 1, 1995
Creator: Keen, N.D.; Frankle, S.C. & MacFarlane, R.E.
Partner: UNT Libraries Government Documents Department

Preliminary analysis of core capsule x-ray spectroscopy and image results for medium-to-high growth factor implosions

Description: Recent capsule implosions using indirect drive on NOVA have probed core and near-core capsule T{sub e}, {rho} and mix structure using non-trivial pulse shapes (i.e. with a foot). These experiments have been performed using smooth as well as artificially roughened capsules. They have been performed using basically 3 non-trivial pulse-shapes with 3 different types of capsules with correspondingly different growth regimes for Rayleigh-Taylor instabilities. These experiments have employed time-dependent spectroscopy, gated imaging and absolutely calibrated time-integrated imaging as x-ray diagnostics. The authors compare nominal and {open_quotes}modified{close_quotes} 1D calculations with the spectroscopic and time-integrated image results. They find that the core T{sub e} is less than calculated (not surprising), but also that the T{sub e} of the inner pusher is substantially higher (at least 20%) than predicted, with perhaps some enhanced mix of the PVA layer towards the core.
Date: September 1, 1995
Creator: Pollak, G.; Delamater, N. & Landen, N.
Partner: UNT Libraries Government Documents Department

Polarized proton acceleration program at the AGS and RHIC

Description: Presented is an overview of the program for acceleration of polarized protons in the AGS and their injection into the RHIC collider. The problem of depolarizing resonances in strong focusing circulator accelerators is discussed. The intrinsic resonances are jumped over by the fast tune jump, and a partial Siberian Snake is used to compensate for over forty imperfection resonances in the AGS. Two sets of full Siberian Snake and spin rotators will be employed in RHIC.
Date: June 1995
Creator: Lee, Y. Y.
Partner: UNT Libraries Government Documents Department

Photon production at CDF and D0

Description: Prompt photon production has been studied in {bar p}p collisions at {radical}s = 1.8 TeV using the CDF and D0 detectors at Fermilab. The measured inclusive isolated photon spectral at CDF and Do are used to test NLO QCD predictions. The CDF result shows that additional soft radiation (K{sub T}) in excess of NLO QCD is required to explain the data. No new resonance is observed in the photon + jet mass spectrum from D0 which is consistent with NLO QCD predictions. The pseudorapidity distribution of the leading jet in photon events at CDF is compared to different parton distribution sets. The angular distribution is found to be better explained by a larger Bremsstrahlung contribution.
Date: July 1, 1995
Creator: Lamoureux, J.I.
Partner: UNT Libraries Government Documents Department

Innovative vitrification for soil remediation

Description: The objective of this DOE demonstration program is to validate the performance and operation of the Vortec Cyclone Melting System (CMS{trademark}) for the processing of LLW contaminated soils found at DOE sites. This DOE vitrification demonstration project has successfully progressed through the first two phases. Phase 1 consisted of pilot scale testing with surrogate wastes and the conceptual design of a process plant operating at a generic DOE site. The objective of Phase 2, which is scheduled to be completed the end of FY 95, is to develop a definitive process plant design for the treatment of wastes at a specific DOE facility. During Phase 2, a site specific design was developed for the processing of LLW soils and muds containing TSCA organics and RCRA metal contaminants. Phase 3 will consist of a full scale demonstration at the DOE gaseous diffusion plant located in Paducah, KY. Several DOE sites were evaluated for potential application of the technology. Paducah was selected for the demonstration program because of their urgent waste remediation needs as well as their strong management and cost sharing financial support for the project. During Phase 2, the basic nitrification process design was modified to meet the specific needs of the new waste streams available at Paducah. The system design developed for Paducah has significantly enhanced the processing capabilities of the Vortec vitrification process. The overall system design now includes the capability to shred entire drums and drum packs containing mud, concrete, plastics and PCB`s as well as bulk waste materials. This enhanced processing capability will substantially expand the total DOE waste remediation applications of the technology.
Date: December 1, 1995
Creator: Jetta, N.W.; Patten, J.S. & Hart, J.G.
Partner: UNT Libraries Government Documents Department

Mechanical properties of high strength aluminum alloys formed by pulsed laser deposition

Description: Very high-strength alloys of A1(O) have been formed using a pulsed laser deposition (PLD) system to deposit from alternating targets of A1 and A1{sub 2}O{sub 3}. Ion beam analysis and transmission electron microscopy show that the deposited material is uniform in composition with up to 33 at. % O and has a highly refined microstructure consisting of a fine, uniform dispersion of {approximately}1 nm diameter {gamma}-A1{sub 2}O{sub 3} precipitates. Ultra-low-load indentation testing combined with finite-element modeling is used to determine the mechanical properties of the layers. Yield stresses as high as 5.1 GPa have been measured in these materials, greatly exceeding the strengths of aerospace Al alloys (-0.5 GPa) and even high strength steels. The key to the properties of these materials is the dispersion of small, hard precipitates spaced only a few Burgers vectors apart; dislocations are apparently unable to cut through and must bow around them.
Date: December 31, 1995
Creator: Knapp, J.A. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Method of estimating maximum VOC concentration in void volume of vented waste drums using limited sampling data: Application in transuranic waste drums

Description: A test program has been conducted at the Idaho National Engineering Laboratory to demonstrate that the concentration of volatile organic compounds (VOCs) within the innermost layer of confinement in a vented waste drum can be estimated using a model incorporating diffusion and permeation transport principles as well as limited waste drum sampling data. The model consists of a series of material balance equations describing steady-state VOC transport from each distinct void volume in the drum. The primary model input is the measured drum headspace VOC concentration. Model parameters are determined or estimated based on available process knowledge. The model effectiveness in estimating VOC concentration in the headspace of the innermost layer of confinement was examined for vented waste drums containing different waste types and configurations. This paper summarizes the experimental measurements and model predictions in vented transuranic waste drums containing solidified sludges and solid waste.
Date: December 1, 1995
Creator: Liekhus, K.J. & Connolly, M.J.
Partner: UNT Libraries Government Documents Department

Dynamics of laser excitation, ionization and harmonic conversion in inert gas atoms

Description: Studies of non-perturbative multiphoton processes in atoms in pulsed laser fields employ a single-active-electron (SAE) model which follows the time evolution of each valence electron in the frozen, mean-field of the remaining electrons, the nucleus and the laser field. The photoelectron and photon emission spectra, although related, are not identical. A simple two-step, quasi-classical model explains the differences and gives a more complete understanding of the strong field induced dynamics.
Date: October 1, 1995
Creator: Kulander, K.C.
Partner: UNT Libraries Government Documents Department

Assembly and testing of a composite heat pipe thermal intercept for HTS current leads

Description: We are building high temperature superconducting (HTS) current leads for a demonstration HTS-high gradient magnetic separation (HGMS) system cooled by a cryocooler. The current leads are entirely conductively cooled. A composite nitrogen heat pipe provides efficient thermal communication, and simultaneously electrical isolation, between the lead and an intermediate temperature heat sink. Data on the thermal and electrical performance of the heat pipe thermal intercept are presented. The electrical isolation of the heat pipe was measured as a function of applied voltage with and without a thermal load across the heat pipe. The results show the electrical isolation with evaporation, condensation and internal circulation taking place in the heat pipe.
Date: September 1, 1995
Creator: Daugherty, M.A.; Daney, D.E.; Prenger, F.C.; Hill, D.D.; Williams, P.M. & Boenig, H.J.
Partner: UNT Libraries Government Documents Department

The Cold War is over. What now?

Description: As you might imagine, the end of the Cold War has elicited an intense reexamination of the roles and missions of institutions such as the Los Alamos National Laboratory. During the past few years, the entire defense establishment has undergone substantial consolidation, with a concomitant decrease in support for research and development, including in areas such as materials. The defense industry is down-sizing at a rapid pace. Even universities have experienced significant funding cutbacks from the defense community. I view this as a profound time in history, bringing changes encompassing much more than just the defense world. In fact, support for science and technology is being reexamined across the board more completely than at any other time since the end of World War II.
Date: May 1995
Creator: Hecker, S. S.
Partner: UNT Libraries Government Documents Department

Energy Systems Division Overview

Description: This report presents an overview of the research programs from the energy systems division in the form of viewgraphs.
Date: August 1, 1995
Creator: Sather, N.
Partner: UNT Libraries Government Documents Department

A transportable high-resolution gamma-ray spectrometer and analysis system applicable to mobile, autonomous or unattended applications

Description: The Safeguards Technology Program at the Lawrence Livermore National Laboratory is developing systems based on a compact electro-mechanically cooled high-purity germanium (HPGe) detector. This detector system broadens the practicality of performing high- resolution gamma-ray spectrometry in the field. Utilizing portable computers, multi-channel analyzers and software these systems greatly improve the ease of performing mobile high-resolution gamma-ray spectrometry. Using industrial computers, we can construct systems that will run autonomously for extended periods of time without operator input or maintenance. These systems can start or make decisions based on sensor inputs rather than operator interactions. Such systems can provide greater capability for wider domain of safeguards, treaty verification application, and other unattended, autonomous or in-situ applications.
Date: July 1, 1995
Creator: Buckley, W.M. & Neufeld, K.W.
Partner: UNT Libraries Government Documents Department

1995 verification flow testing of the HDR reservoir at Fenton Hill, New Mexico

Description: Recent flow testing of the Fenton Hill HDR reservoir has demonstrated that engineered geothermal systems can be shut-in for extended periods of d= with apparently no adverse effects. However, when this particular reservoir at Venton Hill was shut-in for 2 years in a pressurized condition, natural convection within the open-jointed reservoir region appears to have leveled out the preexisting temperature gradient so that the gradient has now approached a condition more typical of liquid-dominated hydrothermal reservoirs which air invariably almost isothermal due to natural convection. As a result of the sudden flow impedance reduction that led to an almost 50% increase in Production flow new the end of the Second Phase of the LTFR in May 1993, we were uncertain as to the state of the reservoir after being shut-in for 2 years. The flow performance observed during the current testing was found to be intermediate between that at-the end of the Second Phase of the LTFT and that following, the subsequent sudden flow increase, implying that whatever caused the sudden reduction in impedance in the first place is probably somehow associated with the cooldown of the reservoir near the injection interval, since temperature recovery at the surfaces of the surrounding open joints is the most obvious phenomenon expected to occur over time within the reservoir.
Date: January 1, 1995
Creator: Brown, D.
Partner: UNT Libraries Government Documents Department

EUV/soft x-ray spectra for low B neutron stars

Description: Recent ROSAT and EUVE detections of spin-powered neutron stars suggest that many emit ``thermal`` radiation, peaking in the EUV/soft X-ray band. These data constrain the neutron stars` thermal history, but interpretation requires comparison with model atmosphere computations, since emergent spectra depend strongly on the surface composition and magnetic field. As recent opacity computations show substantial change to absorption cross sections at neutron star photospheric conditions, we report here on new model atmosphere computations employing such data. The results are compared with magnetic atmosphere models and applied to PSR J0437-4715, a low field neutron star.
Date: May 23, 1995
Creator: Romani, R.W.; Rajagopal, M.; Rogers, F.J. & Iglesias, C.A.
Partner: UNT Libraries Government Documents Department

Measurement of the B{sup +} and B{sup 0} meson lifetimes using exclusive B {yields} {psi}K decays at CDF

Description: The authors present recent CDF measurements of {tau}{sup +}, {tau}{sup 0}, and {tau}{sup +}/{tau}{sup 0} using exclusive B {yields} {psi}K decays, where B = B{sup +} or B{sup 0}, {psi} = J/{psi} or {psi}(2S), and K = K{sup +}, K*(892){sup 0}, K{sub S}{sup 0}, or K*(892){sup +}. The precision of these results is less than 10% and is nearly identical to that previously reported at LEP.
Date: July 1995
Creator: Abe, F.
Partner: UNT Libraries Government Documents Department

Pulsed optically-pumped polarized H{sup {minus}} ion source development

Description: Results are presented of pulsed optically-pumped polarized H{sup {minus}} ion source (OPPIS) development for high energy accelerators. An atomic hydrogen beam intensity of 2 {times} 10{sup 18} atoms/s within the polarizer acceptance was obtained with an atomic H injector at BINP. A pulsed polarized H{sup {minus}} ion current of about 10--20 mA should be obtainable using this injector. Limitations on beam characteristics due to space-charge were studied. A polarization scheme to avoid space-charge limitations is considered, in which charge-exchange and spin-exchange are combined.
Date: September 1, 1995
Creator: Zelenski, A.N.; Davydenko, V.I.; Dimov, G.I.; Levy, C.D.P.; Oers, W.T.H. van; Schmor, P.W. et al.
Partner: UNT Libraries Government Documents Department

Reactor physics calculations for {sup 99}Mo production at the Annular Core Research Reactor

Description: The isotope {sup 99}Mo would be produced at Sandia using ACRR and the collocated Hot Cell Facility. {sup 99}Mo would be produced by irradiating targets coated with {sup 235}U in the form of highly enriched U{sub 3}O{sub 8}; after 7 days, the target would be removed and the isotope extracted using the Cintichem process. The Monte Carlo neutronics computer code MCNP was used to determine the optimum configuration for production, using various fractions of the US demand. Although ACRR operates at a low power level, the US demand for {sup 99}Mo can be easily met using a reasonable number of targets.
Date: July 1, 1995
Creator: Parma, E.J.
Partner: UNT Libraries Government Documents Department

Search for new phenomena in CDF-I: Z{prime}, W{prime} and leptoquarks

Description: We present the latest results of CDF searches for Z{prime}, W{prime} and leptoquarks. Using about 70pb{sup -1} data from 1992-95 CDF runs, we have searched for Z{prime} {yields} l{sup +}l{sup -}, W{prime} {yields} WZ and pairs of second generation scalar leptoquark, S{sub 2}. We find no evidence for these new particles, and set new mass limits at 95% CL. We exclude M{sub Z{prime}} < 650 GeV/c{sup 2}, 205 < M{prime}{sub W} < 400 GeV/c{sup 2}, and M{sub S2} < 180 GeV/c{sup 2} for {beta} = 1 and M{sub S2} < 141 GeV/c{sup 2} for {beta} = 0.5. Two interesting strange events are also shown.
Date: July 1, 1995
Creator: Park, S.
Partner: UNT Libraries Government Documents Department

Advanced materials for solid oxide fuel cells

Description: The purpose of this research is to improve the properties of the current state-of-the-art materials used for solid oxide fuel cells (SOFCs). The objectives are to: (1) develop materials based on modifications of the state-of-the-art materials; (2) minimize or eliminate stability problems in the cathode, anode, and interconnect; (3) Electrochemically evaluate (in reproducible and controlled laboratory tests) the current state-of-the-art air electrode materials and cathode/electrolyte interfacial properties; (4) Develop accelerated electrochemical test methods to evaluate the performance of SOFCs under controlled and reproducible conditions; and (5) Develop and test materials for use in low-temperature SOFCs.
Date: December 31, 1995
Creator: Armstrong, T. & Stevenson, J.
Partner: UNT Libraries Government Documents Department

Scheduled oil sampling: A proactive approach towards pollution prevention and waste minimization

Description: The Waste Reduction Operations Complex (WROC) at the Idaho National Engineering Laboratory (INEL) maintains an emergency fire protection system which provides fire water during emergency conditions. The diesel engine driving this system receives regular preventative maintenance (PM) and servicing. The Waste Minimization Plan for WROC requires that all systems and processes be given a regular assessment to verify any Pollution Prevention (P2) or Waste Minimization (Waste Min.) activities. The WROC Maintenance group has implemented a proactive or best management practice (BMP) that reflects this P2/Waste Min. awareness. The diesel engine is operated for 30 minutes each week to maintain its readiness. A typical owner`s manual for industrial engines require that the oil be changed every 100-hours of operation or 6-months; only 13-hours of operation occur during the 6-months before the required oil change. Thirteen hours of operation would not warrant changing the oil. The WROC proactive approach to this problem is to perform an annual Scheduled Oil Sampling (SOS). An 8-ounce sample of oil is obtained and sent to a SOS lab. The SOS lab analyzes the condition (breakdown) of the oil and, provides a detailed analysis of metal particulates (from engine wear), and checks for impurities, such as, sulphur, water, coolant, and fuel in the system. The oil is changed only when the sampling results warrant that an oil change is necessary. The actual costs of the oil, filters, and labor far exceed the costs of performing the SOS. The projected cost savings after 8 years is about $12,000 in labor, oil changing costs, and hazardous waste analysis.
Date: November 1, 1995
Creator: Reece, C. & Zirker, L.
Partner: UNT Libraries Government Documents Department

Influence of sample composition on aerosol organic and black carbon determinations

Description: In this paper we present results on characterization of filter-collected redwood (Sequoia sempevirens)-needle and eucalyptus smoke particles by thermal, optical, and solvent extraction methods. Our results demonstrate that organic and black carbon concentrations determined by thermal and optical methods are not only method dependent, but also critically influenced by the overall chemical composition of the samples. These conclusions are supported by the following: (1) the organic fraction of biomass smoke particles analyzed includes a component, ranging in concentration from about 6-20% of total carbon or from 16-30% of organic carbon, that is relatively non-volatile and has a combustion temperature close to that of black carbon; (2) presence of K or Na in biomass smoke samples lowers the combustion temperatures of this organic component and of black carbon, making their combustion properties indistinguishable; (3) about 20% of total organic material is nonvolatile when heated to 550{degrees}C in an inert atmosphere. Consequently, thermal methods that rely on a specific temperature to separate organic from black carbon may either underestimate or overestimate the black and organic carbon concentrations, depending on the amounts of Na and K and on the composition and concentration of organic material present in a sample. These analytical uncertainties and, under some conditions, absorption by organic material may contribute to the variability of empirically derived proportionality between light transmission through filter deposits and black carbon concentrations.
Date: July 1, 1995
Creator: Novakov, T. & Corrigan, C.E.
Partner: UNT Libraries Government Documents Department