Occupational dose reduction at Department of Energy contractor facilities: Bibliography of selected readings in radiation protection and ALARA (open access)

Occupational dose reduction at Department of Energy contractor facilities: Bibliography of selected readings in radiation protection and ALARA

This bibliography contains abstracts relating to various aspects of ALARA program implementation and dose reduction activities, with a focus on DOE facilities. Abstracts included in this bibliography were selected from proceedings of technical meetings, journals, research reports, searches of the DOE Energy, Science and Technology Database (in general, the citation and abstract information is presented as obtained from this database), and reprints of published articles provided by the authors. Facility types and activities covered in the scope of this report include: radioactive waste, uranium enrichment, fuel fabrication, spent fuel storage and reprocessing, facility decommissioning, hot laboratories, tritium production, research, test and production reactors, weapons fabrication and testing, fusion, uranium and plutonium processing, radiography, and aocelerators. Information on improved shielding design, decontamination, containments, robotics, source prevention and control, job planning, improved operational and design techniques, as well as on other topics, has been included. In addition, DOE/EH reports not included in previous volumes of the bibliography are in this volume (abstracts 611 to 684). This volume (Volume 5 of the series) contains 217 abstracts. An author index and a subject index are provided to facilitate use. Both indices contain the abstract numbers from previous volumes, as well as the current volume. …
Date: December 1, 1993
Creator: Dionne, B. J.; Sullivan, S. G. & Baum, J. W.
Object Type: Report
System: The UNT Digital Library
Experimental Determination of ETS Particle Deposition in a Low Ventilation Room (open access)

Experimental Determination of ETS Particle Deposition in a Low Ventilation Room

Deposition on indoor surfaces is an important removal mechanism for tobacco smoke particles. We report measurements of deposition rates of environmental tobacco smoke particles in a room-size chamber. The deposition rates were determined from the changes in measured concentrations by correcting for the effects of coagulation and ventilation. The air flow turbulent intensity parameter was determined independently by measuring the air velocities in the chamber. Particles with diameters smaller than 0.25 {micro}m coagulate to form larger particles of sizes between 0.25-0.5 {micro}m. The effect of coagulation on the particles larger than 0.5 {micro}m was found to be negligible. Comparison between our measurements and calculations using Crump and Seinfeld's theory showed smaller measured deposition rates for particles from 0.1 to 0.3 {micro}m in diameter and greater measured deposition rates for particles larger than 0.6 {micro}m at three mixing intensities. Comparison of Nazaroff and Cass model for natural convection flow showed good agreement with the measurements for particles larger than 0.1 {micro}m in diameter, however, measured deposition rates exceeded model prediction by a factor of approximately four for particles in size range 0.05-0.1 {micro}m diameter. These results were used to predict deposition of sidestream smoke particles on interior surfaces. Calculations predict that …
Date: May 1, 1993
Creator: Xu, M.; Nematollahi, M.; Sextro, R. G.; Gadgil, A. J. & Nazaroff, W. W.
Object Type: Article
System: The UNT Digital Library
Space reactor fuel element testing in upgraded TREAT (open access)

Space reactor fuel element testing in upgraded TREAT

The testing of candidate fuel elements at prototypic operating conditions with respect to temperature, power density, hydrogen coolant flow rate, etc., a crucial component in the development and qualification of nuclear rocket engines based on the Particle Bed Reactor (PBR), NERVA-derivative, and other concepts. Such testing may be performed at existing reactors, or at new facilities. A scoping study has been performed to assess the feasibility of testing PBR based fuel elements at the TREAT reactor. initial results suggest that full-scale PBR, elements could be tested at an average energy deposition of {approximately}60--80 MW-s/L in the current TREAT reactor. If the TREAT reactor was upgraded to include fuel elements with a higher temperature limit, average energy deposition of {approximately}100 MW/L may be achievable.
Date: May 1, 1993
Creator: Todosow, M.; Bezler, P.; Ludewig, H. & Kato, W.Y.
Object Type: Article
System: The UNT Digital Library
Fisheries Habitat Evaluation on Tributaries of the Coeur d`Alene Indian Reservation : Annual Report [1991]. (open access)

Fisheries Habitat Evaluation on Tributaries of the Coeur d`Alene Indian Reservation : Annual Report [1991].

The purpose of this study was to conduct physical and biological surveys of streams located on the Coeur d'Alene Indian Reservation. Surveys were designed to collect information on improving spawning habitat, rearing habitat, and access to spawning tributaries for bull trout and cutthroat trout and to evaluate the existing fish stocks. The objectives of the second year of the study were to: (1) Develop a stream ranking system to select the five streams of primary fisheries potential; (2) Conduct physical field surveys; (3) Determine population dynamics; (4) Determine growth rates of existing trout species; (5) Determine macroinvertebrate densities and diversities; and (6) Determine baseline angler utilization. The Missouri method of evaluating stream reaches was modified and utilized to rank the ten tributaries (as determined by Graves et al. 1990) associated with reservation lands. The method incorporated such data as stream bank and bed stability, condition of riparian vegetation, land use, degree of urbanization, passage barriers, water quality, flow and temperature regimes, as well as the overall habitat suitability for all life history stages of cutthroat and bull trout. This data was then combined with relative abundance data, growth rates and invertebrate densities to choose five streams, which offer the best …
Date: February 1, 1993
Creator: Woodward-Lillengreen, Kelly L.; Johnson, D. Chad & Scholz, Allan T.
Object Type: Report
System: The UNT Digital Library
Biodiesel from Microalgae: Complementarity in a Fuel Development Strategy (open access)

Biodiesel from Microalgae: Complementarity in a Fuel Development Strategy

Biodiesel produces fewer pollutants than petroleum diesel, and is virtually free of sulfur. These properties make biodiesel an attractive candidate to facilitate compliance with the Clean Air Act Amendments of 1990 (CAAA). This fuel is ordinarily considered to be derived from oilseeds, but an essentially identical biodiesel can be made from microalgae.
Date: August 1, 1993
Creator: Brown, L. M.
Object Type: Report
System: The UNT Digital Library
Genetic Variation in DNA of Coho Salmon from the Lower Columbia River : Final Report 1993. (open access)

Genetic Variation in DNA of Coho Salmon from the Lower Columbia River : Final Report 1993.

The goal of this project was to develop techniques to provide the information needed to determine if Lower Columbia River coho salmon represent a 'species' under the Endangered Species Act. Our report features two new nuclear DNA approaches to the improved detection of genetic variation: (1) Studies of DNA-level genetic variation for two nuclear growth hormone genes; (2) Use of arbitrary DNA primers (randomly amplified polymorphic DNA, or 'RAPD' primers) to detect variation at large numbers of nuclear genes. We used the polymerase chain reaction (PCR) to amplify variable sections (introns) of two growth hormone genes (GH-I and G/f-Z) in several salmonid species. Coho salmon had three DNA length variants for G/-I intron C. Restriction analysis and sequencing provided valuable information about the mode of evolution of these DNA sequences. We tested segregation of the variants in captive broods of coho salmon, and demonstrated that they are alleles at a single Mendelian locus. Population studies using the GH-1 alleles showed highly significant frequency differences between Lower Columbia River and Oregon Coast coho salmon, and marginal differences among stocks within these regions. These new markers are adequately defined and tested to use in coho salmon population studies of any size. The …
Date: April 1, 1993
Creator: Fobes, Stephen; Knudsen, Kathy & Allendorf, Fred
Object Type: Report
System: The UNT Digital Library
Velocity and Attenuation Structure of the Geysers Geothermal Field, California (open access)

Velocity and Attenuation Structure of the Geysers Geothermal Field, California

The Geysers geothermal field is located in northern California and is one of the world's largest producers of electricity from geothermal energy. The resource consists of primarily dry steam which is produced from a low, porosity fractured graywacke. Over the last several years steam pressure at the Geysers has been dropping. Concern over decline of the resource has prompted research to understand its fundamental nature. A key issue is the distribution of fluid in the matrix of the reservoir rock. In this paper we interpret seismic compressional-wave velocity and attenuation data at the Geysers in terms of the geologic structure and fluid saturation in the reservoir. Our data consist of approximately 300 earthquakes that are of magnitude 1.2 and are distributed in depth between sea level and 2.5 km. Using compressional-wave arrival times, we invert for earthquake location, origin time, and velocity along a three-dimensional grid. Using the initial pulse width of the compressional-wave, we invert for the initial pulse width associated with the source, and the one-dimensional Q structure. We find that the velocity structure correlates with known mapped geologic units, including a velocity high that is correlated with a felsite body at depth that is known from drilling. …
Date: January 1, 1993
Creator: Zucca, J. J.; Hutchings, L. J. & Kasameyer, P. W.
Object Type: Article
System: The UNT Digital Library
Impacts of a Sub-Slab Aggregate Layer and a Sub-Aggregate Membrane on Radon Entry Rate: A Numerical Study (open access)

Impacts of a Sub-Slab Aggregate Layer and a Sub-Aggregate Membrane on Radon Entry Rate: A Numerical Study

A subslab aggregate layer can increase the radon entry rate into a building by up to a factor of 5. We use a previously tested numerical technique to investigate and confirm this phenomenon. Then we demonstrate that a sub-aggregate membrane has the potential to significantly reduce the increase in radon entry rate due to the aggregate layer, even when a gap exists between the perimeter of the membrane and the footer. Such membranes greatly reduce diffusion of radon from the soil into the aggregate and are impermeable to flow. Radon entry through the basement floor slab is limited to radon entry through the holes in the membrane. In addition, a sub-aggregate membrane is predicted to improve the performance of active sub-slab ventilation systems and makes passive systems more promising.
Date: January 1, 1993
Creator: Bonnefous, Y. C.; Gadgil, A. J.; Revzan, K. L.; Fisk, W. J. & Riley, W. J.
Object Type: Article
System: The UNT Digital Library
Economic Analysis of Ilumex, A Project to Promote Energy-Efficient Residential Lighting in Mexico (open access)

Economic Analysis of Ilumex, A Project to Promote Energy-Efficient Residential Lighting in Mexico

A higher penetration of compact fluorescent lamps (CFLs) for household lighting can reduce growth in peak electricity demand, reduce sales of subsidized electricity, and lessen environmental impacts. This paper describes an economic analysis of a project designed to promote high penetration rates of CFLs in two cities in Mexico. Our analysis indicates that the project will bring substantial net economic benefits to Mexico, the utility, and the average customer. In the absence of any subsidy to CFLs, most customers will see a payback period longer than two years. By sharing some of the anticipated net benefit, CFE, the utility company, can reduce the payback period to a maximum of two years for all customers. CFE's role is thus crucial to the successful implementation of the project. Expanding the Ilumex project to a Mexico-wide program would make a significant contribution towards meeting the planned addition of generation capacity by the year 2000.
Date: November 1, 1993
Creator: Sathaye, Jayant A.; Friedmann, R.; Meyers, S.; de Buen, O.; Gadgil, A. J.; Vargas, E. et al.
Object Type: Article
System: The UNT Digital Library
The Distribution of Exposure to Radon: Effects of Population Mobility (open access)

The Distribution of Exposure to Radon: Effects of Population Mobility

The distribution of population exposures to radon, rather than the distribution of indoor radon concentrations, determines the fraction of population exposed to exceptionally high risk from radon exposures. Since this fraction at high risk has prompted the development of public policies on radon, it is important to first determine the magnitude of this fraction, and then how it much would decrease with different implementation program options for radon mitigation. This papers presents an approach to determining the distribution of population exposures to radon from public domain data, and illustrates it with application to the state of Minnesota. During this work, we are led to define a radon entry potential index which appears useful in the search for regions with high radon houses.
Date: January 1, 1993
Creator: Gadgil, A. J.; Rein, S.; Nero, A. V. & Wollenberg Jr., H. A.
Object Type: Article
System: The UNT Digital Library
Shielding and Criticality Analyses of Phase I Reference Truck and Rail Cask Designs for Spent Nuclear Fuel (open access)

Shielding and Criticality Analyses of Phase I Reference Truck and Rail Cask Designs for Spent Nuclear Fuel

This work was performed in support of the planned Phase I request for proposals (RFP) for spent nuclear fuel (SNF) transportation cask designs. The funding for this work was provided by the Office of Civilian Radioactive Waste Management (OCRWM) through its M&O contractor, TRW Environmental Safety Systems (TESS). The objective of this work was to prepare for the criticality and shielding evaluation of the Phase I cask design proposals by investigating the effect of SNF and design variables on reference cask models. Prior knowledge in this area should mitigate the analysis effort required for the bid evaluation process. The effect of SNF burnup/age characteristics on payload, the effect of initial enrichment on the radiation source and dose, and the relative effectiveness of several gamma-ray and neutron shield materials were all areas of investigation. In addition, the results of this effort provide data that can be used to assess the practicality of the RFP specifications regarding the targeted performance of the Phase I casks. Although the final RFP for the Phase I cask was never issued, this report has been issued because of its potential value in future SNF cask design efforts. Results are presented herein to determine the adequacy with …
Date: January 1, 1993
Creator: Broadhead, B.L.
Object Type: Report
System: The UNT Digital Library
Alternative Feedstocks Program Technical and Economic Assessment: Thermal/Chemical and Bioprocessing Components (open access)

Alternative Feedstocks Program Technical and Economic Assessment: Thermal/Chemical and Bioprocessing Components

This resource document on biomass to chemicals opportunities describes the development of a technical and market rationale for incorporating renewable feedstocks into the chemical industry in both a qualitative and quantitative sense. The term "renewable feedstock?s" can be defined to include a huge number of materials such as agricultural crops rich in starch, lignocellulosic materials (biomass), or biomass material recovered from a variety of processing wastes.
Date: July 1, 1993
Creator: Bozell, J. J. & Landucci, R.
Object Type: Report
System: The UNT Digital Library
Modeling Emissions of Volatile Organic Compounds from New Carpets (open access)

Modeling Emissions of Volatile Organic Compounds from New Carpets

A simple model is proposed to account for observed emissions of volatile organic compounds (VOCs) from new carpets. The model assumes that the VOCs originate predominantly in a uniform slab of polymer backing material. Parameters for the model (the initial concentration of a VOC in the polymer, a diffusion coefficient and an equilibrium polymer/air partition coefficient) are obtained from experimental data produced by a previous chamber study. The diffusion coefficients generally decrease as the molecular weight of the VOCs increase, while the polymer/air partition coefficients generally increase as the vapor pressure of the compounds decrease. In addition, for two of the study carpets that have a styrene-butadiene rubber (SBR) backing, the diffusion and partition coefficients are similar to independently reported values for SBR. The results suggest that predictions of VOCs emissions from new carpets may be possible based solely on a knowledge of the physical properties of the relevant compounds and the carpet backing material. However, a more rigorous validation of the model is desirable.
Date: February 1, 1993
Creator: Little, J. C.; Hodgson, A. T. & Gadgil, A. J.
Object Type: Article
System: The UNT Digital Library
Technical Design of Hadron Therapy Facilities (open access)

Technical Design of Hadron Therapy Facilities

Radiation therapy with hadron beams now has a 40-year track record at many accelerator laboratories around the world, essentially all of these originally physics-research oriented. The great promise shown for treating cancer has led the medical community to seek dedicated accelerator facilities in a hospital setting, where more rapid progress can be made in clinical research. This paper will discuss accelerator and beam characteristics relevant to hadron therapy, particularly as applied to hospital-based facilities. A survey of currently-operating and planned hadron therapy facilities will be given, with particular emphasis on Lorna Linda (the first dedicated proton facility in a hospital) and HIMAC (the first dedicated heavy-ion medical facility).
Date: August 1, 1993
Creator: Alonso, J. R.
Object Type: Article
System: The UNT Digital Library
ELISA-Based Segregation of Adult Spring Chinook Salmon for Control of Bacterial Kidney Disease: Annual Report 1991. (open access)

ELISA-Based Segregation of Adult Spring Chinook Salmon for Control of Bacterial Kidney Disease: Annual Report 1991.

Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum (RS), a serious disease of salmonid fish worldwide. The disease has a major impact on spring chinook salmon populations in the Columbia River system. There is strong evidence that RS can be transmitted from parent to progeny, and segregation of progeny based on levels of antigen detected in adult fish may obviate this mode of transmission. Results are presented from the third year of a four year study to investigate segregation of broodstock as a tool for controlling BKD. Segregation of adult fish infected with RS has been achieved using enzyme-linked immunosorbent assays (ELlSAs) optimized in the first and second year of this project. Gametes from both 1990 and 1991 broodstock, either injected with erythromycin or receiving no antibiotic injection were successfully segregated into groups having either high or low levels of the RS soluble antigen. Offspring have been monitored every three months from the 1990 broodstock and are being monitored from the 1991 broodstock. Antigen levels in the offspring from the 1990 segregation experiment at Marion Forks Hatchery were low and clinical BKD was not observed in any of the juvenile fish. At Carson National Fish Hatchery, antigen levels were also …
Date: February 1, 1993
Creator: Kaattari, Stephen L.
Object Type: Report
System: The UNT Digital Library
Umatilla River Basin Anadromous Fish Habitat Enhancement Project : 1993 Annual Report. (open access)

Umatilla River Basin Anadromous Fish Habitat Enhancement Project : 1993 Annual Report.

The Umatilla Basin Anadromous Fish Habitat Enhancement Project is funded under the Northwest Power Planning Council's Columbia River Basin Fish and Wildlife Program Measure 704 (d) (1) 34.02 and targets the improvement of water quality and restoration of riparian areas, holding, spawning and rearing habitats of steelhead, spring and fall chinook and coho salmon. The project focused on implementing instream and riparian habitat improvements on private lands on the Umatilla Indian Reservation (hereafter referred to as Reservation) from April 1, 1988 to March 31, 1992. These efforts resulted in enhancement of the lower 1/4 mile of Boston Canyon Creek, the lower 4 river miles of Meacham Creek and 3.2 river miles of the Umatilla River (downstream of the Meacham Creek confluence upstream to the Reservation East Boundary). In 1993, the project shifted emphasis to a comprehensive watershed approach consistent with other basin efforts and began to identify upland and riparian watershed-wide causative factors impacting fisheries habitat and natural fisheries production capabilities throughout the Umatilla River Watershed. Maintenance of existing habitat improvement projects was included under this comprehensive approach. Maintenance of existing gravel traps, instream and bank stabilization structures was required within project areas during the reporting period due to spring …
Date: April 1, 1993
Creator: Shaw, R. Todd
Object Type: Report
System: The UNT Digital Library
Geomorphology of plutonium in the Northern Rio Grande (open access)

Geomorphology of plutonium in the Northern Rio Grande

Nearly all of the plutonium in the natural environment of the Northern Rio Grande is associated with soils and sediment, and river processes account for most of the mobility of these materials. A composite regional budget for plutonium based on multi-decadal averages for sediment and plutonium movement shows that 90 percent of the plutonium moving into the system is from atmospheric fallout. The remaining 10 percent is from releases at Los Alamos. Annual variation in plutonium flux and storage exceeds 100 percent. The contribution to the plutonium budget from Los Alamos is associated with relatively coarse sediment which often behaves as bedload in the Rio Grande. Infusion of these materials into the main stream were largest in 1951, 1952, 1957, and 1968. Because of the schedule of delivery of plutonium to Los Alamos for experimentation and weapons manufacturing, the latter two years are probably the most important. Although the Los Alamos contribution to the entire plutonium budget was relatively small, in these four critical years it constituted 71--86 percent of the plutonium in bedload immediately downstream from Otowi.
Date: March 1, 1993
Creator: Graf, William L.
Object Type: Report
System: The UNT Digital Library
A beamline design and data acquisition with the 20-MeV, 20-ps electron beam for the higher-order mode studies of the APS SR-rf cavities (open access)

A beamline design and data acquisition with the 20-MeV, 20-ps electron beam for the higher-order mode studies of the APS SR-rf cavities

A beamline has been designed and assembled to use the ANL Chemistry Division 20-MeV electron linac for the testing of higher-order mode excitation and damping in rf cavities. The beamline consists of two sections (a beam collimating section with a 1.5 inches-OD vacuum line, and a cavity test section with a 3 inches-OD vacuum line), separated by two double aluminum foil windows. The beam diagnostics consist of a stripline beam position monitor, integrating current transformers, fluorescent screens, and a Faraday cup. EPICS (Experimental Physics and Industrial Control System) is used for beamline control, monitoring, and data acquisition. Also described is the diagnostic system used for beam image capture and analysis using EPICS-controlled hardware and PV-WAVE software. The rf cavity measurement will be described in a separate paper.
Date: January 1, 1993
Creator: Song, J.; Nassiri, A. & Daly, R.
Object Type: Article
System: The UNT Digital Library
Pilot study risk assessment for selected problems at the Nevada Test Site (NTS) (open access)

Pilot study risk assessment for selected problems at the Nevada Test Site (NTS)

The Nevada Test Site (NTS) is located in southwestern Nevada, about 105 km (65 mi) northwest of the city of Las Vegas. A series of tests was conducted in the late 1950s and early 1960s at or near the NTS to study issues involving plutonium-bearing devices. These tests resulted in the dispersal of about 5 TBq of [sup 239,24O]Pu on the surficial soils at the test locations. Additionally, underground tests of nuclear weapons devices have been conducted at the NTS since late 1962; ground water beneath the NTS has been contaminated with radionuclides produced by these tests. These two important problems have been selected for assessment. Regarding the plutonium contamination, because the residual [sup 239]Pu decays slowly (half-life of 24,110 y), these sites could represent a long-term hazard if they are not remediated and if institutional controls are lost. To investigate the magnitude of the potential health risks for this no-remediation case, three basic exposure scenarios were defined that could bring individuals in contact with [sup 239,24O]Pu at the sites: (1) a resident living in a subdivision, (2) a resident farmer, and (3) a worker at a commercial facility -- all located at a test site. The predicted cancer risks …
Date: June 1, 1993
Creator: Daniels, J.I. (ed.)
Object Type: Report
System: The UNT Digital Library
High precision beam alignment of electromagnetic wigglers (open access)

High precision beam alignment of electromagnetic wigglers

The performance of Free-Electron Lasers depends critically on the quality of the alignment of the electron beam to the wiggler's magnetic axis and the deviation of this axis from a straight fine. The measurement of the electron beam position requires numerous beam position monitors in the wiggler, where space is at premium. The beam position measurement is used to set beam steerers for an orbit correction in the wiggler. The authors propose an alternative high precision alignment method in which one or two external Beam Position Monitors (BPM) are used. In this technique, the field in the electro-wiggler is modulated section by section and the beam position movement at the external BPM is detected in synchronism with the modulation. A beam offset at the modulated beam section will produce a modulation of the beam position at the detector that is a function of the of the beam offset and the absolute value of the modulation current. The wiggler errors produce a modulation that is a function of the modulation current. It will be shown that this method allows the detection and correction of the beam position at each section in the presence of wiggler errors with a good resolution. Furthermore, …
Date: January 1, 1993
Creator: Ben-Zvi, Ilan & Qiu, X. Z.
Object Type: Article
System: The UNT Digital Library
The development of in vitro mutagenicity testing systems using T-lymphocytes (open access)

The development of in vitro mutagenicity testing systems using T-lymphocytes

This annual report describes progress in studies on hprt mutations induced by radon or Indium 111 along with the corresponding mutation frequency, cloning and molecular spectra in human T-lymphocytes. Parallel studies on the mutation susceptibility between individuals is being investigated by hprt mutation studies on ataxia telangiectasia and xeroderma pigmentosum.
Date: May 1, 1993
Creator: Albertini, R.J.
Object Type: Report
System: The UNT Digital Library
Diffuse scattering and image contrast of tweed in superconducting oxides: A simulation and interpretation (open access)

Diffuse scattering and image contrast of tweed in superconducting oxides: A simulation and interpretation

Monte Carlo simulations were performed with a lattice gas model which represents the interactions between oxygen atoms in YBa[sub 2](Cu[sub 1-x]M[sub x])[sub 3]O[sub 7+[delta]] (M=Fe, Co, or Al, 0.03< [times] <0.l) system. The amplitudes of concentration waves/displacement waves obtained from these simulations then were used to calculate the intensity of the diffuse scattering of tweed seen in the electron diffraction pattern. The characteristic features of the tweed image were produced by calculation, using a model based on the contrast originating from structures with displacive modulation, stacking on the top of each other. Both calculations agree well with the TEM observations and provide an useful basis for a better insight into the origin of the tweed structure.
Date: January 1, 1993
Creator: Zhu, Yimei & Cai, Zhi-Xiong.
Object Type: Article
System: The UNT Digital Library
Determination of the energy of suprathermal electrons during lower hybrid current drive on PBX-M (open access)

Determination of the energy of suprathermal electrons during lower hybrid current drive on PBX-M

Suprathermal electrons are diagnosed by a hard x-ray pinhole camera during lower hybrid current drive on PBX-M. The experimental hard x-ray images are compared with simulated images, which result from an integration of the relativistic bremsstrahlung along lines-of-sight through the bean-shaped plasma. Images with centrally peaked and radially hollow radiation profiles are easily distinguished. The energy distribution of the suprathermal electrons is analyzed by comparing images taken with different absorber foils. An effective photon temperature is derived from the experimental images, and a comparison with simulated photon temperatures yields the energy of the suprathermal electrons. The analysis indicates that the energy of the suprathermal electrons in the hollow discharges is in the 50 to 100 key range in the center of the discharge. There seems to exist a very small higher energy component close to the plasma edge.
Date: June 1, 1993
Creator: Von Goeler, S.; Bernabei, S.; Davis, W.; Ignat, D.; Kaita, R.; Roney, P. et al.
Object Type: Article
System: The UNT Digital Library
Reorientation of misfit dislocations during annealing in InGaAs/GaAs(001) interfaces (open access)

Reorientation of misfit dislocations during annealing in InGaAs/GaAs(001) interfaces

Transmission electron microscopy is applied to investigate the effect of postannealing on misfit dislocations in an In[sup 0.2]Ga[sup 0.8]As/GaAs(001) heterostructure. An orthogonal array of 60[degree] dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520C. When the as-grown samples were annealed at temperatures ranging from 600 to 800C, the 60[degree] dislocations were gradually reoriented by dislocation reactions occurring at the 90[degree] intersections followed by nonconservative motion driven by dislocation line tension and the residual elastic misfit strain. The final result of this process was a dislocation array lying along [100] and [center dot] [010] directions. The reoriented u =<100> dislocation has a Burgers vector b = a/2 <101>, which is the same as that of 60[degree] dislocation, but the edge component of its Burgers vector in the (001) interfacial plane is larger than that of 60[degree] dislocation by a factor of [radical]2, resulting in a greater contribution to elastic strain relaxation. This nonconservative reorientation of 60[degree] dislocations to form the u=<100> dislocations represents a new strain relaxation mechanism in diamond or zinc blende semiconductor heterostructures.
Date: April 1, 1993
Creator: Chen, Y.; Liliental-Weber, Z.; Washburn, J. (Lawrence Berkeley Lab., CA (United States)); Klem, J.F. & Tsao, J.Y. (Sandia National Labs., Albuquerque, NM (United States))
Object Type: Article
System: The UNT Digital Library