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Study of the anisotropy of the threshold energy in copper using in-situ electrical resistivity measurements in the HVEM

Description: In the past, electrical-resistivity measurements and high voltage electron microscopy-(HVEM) have been used separately to investigate the anisotropy of the threshold energy for Frenkel-pair production. Electrical resistivity, measured in a conventional electron accelerator, has been used to observe small changes in the concentration of isolated Frenekel pairs at low temperatures, while HVEM experiments have focussed on the observation of measurable changes in visible defect clusters, primarily at elevated temperatures. However, quantitative comparison of the threshold energies obtained with the two techniques has proved difficult. As a first step toward resolving this dilemma, the threshold-energy surface for copper was determined by in-situ electrical-resistivity measurements below 10 K in the HVEM. By combining the advantages of both techniques, this approach allowed a precise and detailed study of the anisotropy of the threshold energy for Frenkel-pair production.
Date: January 1, 1980
Creator: King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Electronic structure studies of YBa[sub 2]Cu[sub 3]O[sub x](6. 2 [le] x [le] 6. 9) using angle resolved photoemission

Description: Using high resolution angle resolved photoemission, the electronic structure of YBa[sub 2]Cu[sub 3]O[sub x] is examined when oxygen stoichiometries are varied in the range 6.2 [le] [times] [le] 6.9. Detailed measurements of the Fermi surface for YBa[sub 2]Cu[sub 3]O[sub 6.9] are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.
Date: November 1, 1992
Creator: Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Downey, J.W. (Argonne National Lab., IL (United States)); Shi, Hao (Argonne National Lab., IL (United States) Missouri Univ., Kansas City, MO (United States). Dept. of Physics) et al.
Partner: UNT Libraries Government Documents Department

Self-diffusion of Er and Hf inpure and HfO/sub 2/-doped polycrystalline Er/sub 2/O/sub 3/. [Hf-175 and Er-169]

Description: Using a tracer technique, self-diffusion of Er and Hf was measured over the approximate temperature interval of 1600 to 1970/sup 0/C in pure and HfO/sub 2/-doped polycryatalline Er/sub 2/O/sub 3/. Up to about 10 m/o HfO/sub 2/ dopant level, the Er self-diffusion coefficients followed a relationship based on cation vacancies. Above 10 m/o HfO/sub 2/, deviation from this relationship occurred, apparently due to clustering of cation vacancies and oxygen interstitials around the dopant hafnia ion. The activation energy for the self-diffusion of Er in pure Er/sub 2/O/sub 3/ was 82.2 Kcal/mole and increased with the HfO/sub 2/ dopant level present. Self-diffusion of Hf was measured in pure Er/sub 2/O/sub 3/ having two impurity levels, and a separation of the grain boundary. The volume diffusion of Hf showed both extrinsic and intrinsic behavior with the transition temperature increasing with the impurity level present in Er/sub 2/O/sub 3/. The activation energy for Hf volume diffusion in the intrinsic region was high, i.e. 235 -+ 9.5 Kcal/mole. The grain boundary diffusion was apparently extrinsic over the entire temperature interval Very low Hf self diffusion rates were found in both pure and HfO/sub 2/ doped Er/sub 2/O/sub 3/ compositions. Despite a clustering effect, the HfO/sub 2/ dopant increased the Hf volume diffusion coefficients.
Date: January 1, 1979
Creator: Scheidecker, R.W.
Partner: UNT Libraries Government Documents Department

Positron annihilation in solid and liquid Ni

Description: New techniques have been developed for the study of metals via positron annihilation which provide for the in-situ melting of the samples and subsequent measurements via Doppler broadening of positron-annihilation radiation. Here we report these metods currently in use at our laboratory; ion implantation of /sup 58/Co and the use of Al/sub 2/O/sub 3/ crucibles for in-situ melting followed by the decomposition of the Doppler-broadened spectrum into a parabolic and a Gaussian component. Our earliest results obtained for pure Ni in the polycrystalline solid and in the liquid state are compared. An interesting similarity is reported for the distributions of the high-momentum (Gaussian) component for positrons annihilating in vacancies at high temperatures and those annihilating in liquid Ni.
Date: March 1, 1982
Creator: Fluss, M.J.; Smedskjaer, L.C.; Chakraborty, B. & Chason, M.K.
Partner: UNT Libraries Government Documents Department

Diffusion studies in amorphous NiZr alloys

Description: Tracer impurity and self diffusion measurements have been made on amorphous (a-) NiZr alloys using radioactive tracer, Secondary Ion Mass Spectrometry and Rutherford backscattering techniques. The temperature dependence of diffusion in a-NiZr can be represented in the form D = D/sub 0/exp(-Q/kT), with no structural relaxation effects being observed. The mobility of an atom in a-NiZr increased dramatically with decreasing atomic radius of the diffusing atom and also with decreasing Ni content for Ni concentrations below approx. =40 at. %. These diffusion characteristics in a-NiZr are remarkably similar to those in ..cap alpha..-Zr and ..cap alpha..-Ti. These mechanisms assume that Zr and Ti provide a close packed structure, either crystalline or amorphous, through which small atoms diffuse by an interstitial mechanism and large atoms diffuse by a vacancy mechanism. 12 refs., 2 figs., 2 tabs.
Date: June 1, 1987
Creator: Hahn, H.; Averback, R.S.; Hoshino, K. & Rothman, S.J.
Partner: UNT Libraries Government Documents Department

PAC spectroscopy of electronic ceramics

Description: Dilute indium dopants in cerium oxides and YBa{sub 2}Cu{sub 3}O{sub x} have been studied by{sup 111}In/Cd Perturbed Angular Correlation (PAC) spectroscopy. By controlling oxygen vacancy concentration in the cerium oxides through doping or high-temperature vacuum annealing, we have found that indium always forms a defect complex unless the sample is doped to reduce greatly the oxygen vacancy concentration. Three different vacancy-associated complexes are found with concentrations that depend on doping and oxygen stoichiometry. Another defect complex occurs in samples having negligible vacancy concentration. At low temperatures, evidence is found of interaction with an electronic hole trapped by {sup 111}Cd after the radioactive decay of the {sup 111}In parent. In YBa{sub 2}Cu{sub 3}O{sub x} the indium substitutes preferentially at the Y site but has measurable probability of substitution in at least one of the two copper sites. A symmetry change near 650 {degree}C is consistent with the well-documented orthorhombic/tetragonal transition for samples in air or oxygen.
Date: January 1, 1991
Creator: Gardner, J.A.; Wang, Ruiping; Schwenker, R. (Oregon Univ., Eugene, OR (United States). Dept. of Physics); Evenson, W.E. (Brigham Young Univ., Provo, UT (United States). Dept. of Physics and Astronomy); Rasera, R.L. (Maryland Univ., Catonsville, MD (United States). Dept. of Physics) & Sommers, J.A. (Teledyne-Wah Chang, Albany, OR (United States))
Partner: UNT Libraries Government Documents Department

Recent studies on radiation induced F-center and colloid particle formation in synthetic NaCl and natural rock salt

Description: Radiation induced F-center and Na metal colloid formation have been studied, at temperatures between 100 and 350/sup 0/C, in melt growth synthetic NaCl crystals and natural rock salt samples, using equipment for making optical measurements during 1 to 3 MeV electron irradiation. In both types of NaCl the damage formation kinetics are qualitatively similar. However, there are large quantitative differences which depend on irradiation temperature, dose rate, total dose, inherent strain, strain applied prior to irradiation and other factors. Natural rock salt samples from different localities exhibit markedly different radiation induced colloid formation rates. An extrapolation of the current data to the doses expected in radioactive waste depositories indicate that natural salt immediately adjacent to the planned waste canisters could develop between 0.1 and 50% colloidal sodium in 40 to 1000 years. 3 figures.
Date: January 1, 1982
Creator: Levy, P.W.; Loman, J.M.; Swyler, K.J. & Dougherty, D.R.
Partner: UNT Libraries Government Documents Department

Studying oxygen vacancies in ceramics by perturbed angular correlation spectroscopy

Description: Perturbed angular correlation measurements in tetragonal and cubic zirconia and in ceria are described. A physically reasonable and self-consistent interpretation of these data implies that oxygen vacancies are trapped at a second neighbor position by Cd in tetragonal zirconia and by In in ceria. For Cd in tetragonal zirconia, the vacancy trap energy is found to be 0.44 eV, and the energy barrier between adjacent trap sites is approximately 0.8 eV. The activation energy of an oxygen vacancy hopping between trap sites around {sup 111}Cd in ceria is found to be 0.55 eV. The activation energy for oxygen vacancy hopping in cubic zirconia, as detected by {sup 181}Ta PAC, is about 1.0 eV and independent of the Y concentration. 12 refs., 4 figs.
Date: January 1, 1990
Creator: Su, Han-Tzong; Wang, Ruiping; Fuchs, H.; Gardner, J.A. (Oregon State Univ., Corvallis, OR (USA). Dept. of Physics); Evenson, W.E. (Brigham Young Univ., Provo, UT (USA). Dept. of Physics) & Sommers, J.A. (Teledyne-Wah Chang, Albany, OR (USA))
Partner: UNT Libraries Government Documents Department

Effects of 50/degree/C surveillance and test reactor irradiations on ferritic pressure vessel steel embrittlement

Description: The results of surveillance tests on the High-Flux Isotope Reactor (HFIR) pressure vessel at the Oak Ridge National Laboratory revealed that a greater than expected embrittlement had taken place after about 17.5 effective full-power years of operation and an operational assessment program was undertaken to fully evaluate the vessel condition and recommend conditions under which operation could be resumed. A research program was undertaken that included irradiating specimens in the Oak Ridge Research Reactor. Specimens of the A212 grade B vessel shell material were included, along with specimens from a nozzle qualification weld and a submerged-arc weld fabricated at ORNL to reproduce the vessel seam weld. The results of the surveillance program and the materials research program performed in support of the evaluation of the HFIR pressure vessel are presented and show the welds to be more radiation resistant than the A212B. Results of irradiated tensile and annealing experiments are described as well as a discussion of mechanisms which may be responsible for enhanced hardening at low damage rates. 20 refs., 22 figs., 5 tabs.
Date: January 1, 1988
Creator: Nanstad, R.K.; Iskander, S.K.; Rowcliffe, A.F.; Corwin, W.R. & Odette, G.R.
Partner: UNT Libraries Government Documents Department

Radiation damage studies on natural rock salt from various geological localities of interest to the radioactive waste disposal program

Description: As part of a program to investigate radiation damage in geological materials of interest to the radioactive waste disposal program, radiation damage, particularly radiation induced sodium metal colloid formation, has been studied in 14 natural rock salt samples. All measurements were made with equipment for making optical absorption and other measurements on samples, in a temperature controlled irradiation chamber, during and after 0.5 to 3.0 MeV electron irradiation. Samples were chosen for practical and scientific purposes, from localities that are potential repository sites and from different horizons at certain localities.
Date: January 1, 1981
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department

Radiation induced F-center and colloid formation in synthetic NaCl and natural rock salt: applications to radioactive waste repositories. [1 to 3 MeV electrons]

Description: Radiation damage, particularly Na metal colloid formation, has been studied in synthetic NaCl and natural rock salt using unique equipment for making optical absorption, luminescence and other measurements during irradiation with 1 to 3 MeV electrons. Previous studies have established the F-center and colloid growth phenomenology. At temperatures where colloids form most rapidly, 100 to 250 C, F-centers appear when the irradiation is initiated and increase at a decreasing rate to a plateau, reached at doses of 10/sup 6/ to 10/sup 7/ rad. Concomitant colloid growth is described by classical nucleation and growth curves with the transition to rapid growth occurring at 10/sup 6/ to 10/sup 7/ rad. The colloid growth rate is low at 100 C, increases markedly to a maximum at 150 to 175 C and decreases to a negligible rate at 225 C. At 1.2x10/sup 8/ rad/h the induction period is >10/sup 4/ sec at 100 C, <3000 sec at 150 to 175 C and >10/sup 4/ sec at 275 C. The colloid growth in salt from 14 localities is well described by C(dose)/sup n/ relations. Data on WIPP site salt (Los Medanos, NM, USA) has been used to estimate roughly the colloid expected in radioactive waste repositories. Doses of 1 to 2x10/sup 10/ rad, which will accumulate in salt adjacent to lightly shielded high level canisters in 200 to 500 years, will convert between 1 and 100% of the salt to Na colloids (and Cl) if back reactions or other limiting reactions do not occur. Each high level lightly shielded canister may ultimately be surrounded by 200 to 300 kg of colloid sodium. Low level or heavily shielded canisters may produce as little as 1 kg sodium.
Date: January 1, 1983
Creator: Levy, P.W.; Loman, J.M. & Kierstead, J.A.
Partner: UNT Libraries Government Documents Department

Slow positron studies on single crystals of Ag(100), Ag(111) and Cu(111). [0 to 5 KeV, 300 to 1200/sup 0/K]

Description: Monoenergetic positrons were employed to examine positronium formation as a function of sample temperature (300 to 1200 K) and incident energy (0 to 5 keV) on Ag(100), Ag(111) and Cu(111) surfaces with submonolayer contamination. In these metals at the higher temperatures, positronium formation becomes the dominant process. A one-dimensional diffusion model is fit to the data as a function of incident energy. Th positronium fraction is found to be an activated process and is identified as detrapping from a surface state and an estimate of the depth of this trap is extracted. The diffusion length is found to be temperature independent before the onset of vacancy trapping. At the higher temperatures vacancy trapping is observed by the decrease in the positron diffusion length at the higher incident voltages. A vacancy formation energy is extracted from the data and is generally lower than the accepted bulk values. 18 references.
Date: January 1, 1979
Creator: Lynn, K.G.
Partner: UNT Libraries Government Documents Department

Defect states in plasma-deposited a-Si:H. Final report, February 1979-January 1980

Description: Studies of defects in plasma-deposited, hydrogenated amorphous silicon (a-Si:H), covering the period February 1979-January 1980 are described. Substantial progress has been made in understanding defect structures, their electronic properties and the influence of doping. The two most significant results are surprising, in one case for simplicity where complexity was expected, and in the other for complexity where simplicity had been presumed. In the first study we have clarified the nature of the defects by showing the connection between luminescence and light induced ESR experiments. The results indicate that dangling bonds having a positive electronic correlation energy are sufficient to explain most of the experimental information. The second study demonstrates the existence of microstructural inhomogeneities, arising from the nucleation and growth of the films. Thus the usual assumption of a uniform alloy with a random distribution of defects must be modified in considering processes such as electrical conduction, trapping, recombination, hydrogen effusion, etc. Of considerable technological and fundamental interest is the influence of doping on the defect behavior. Previous indications that doping introduces defect states have been confirmed. It remains to determine why this behavior occurs, and if there are any means of circumventing the problem.
Date: February 15, 1980
Creator: Knights, J C
Partner: UNT Libraries Government Documents Department

Isotope effect for cation diffusion in CoO

Description: The simultaneous diffusion of /sup 55/Co and /sup 60/Co has been measured in CoO as a function of equilibrium oxygen pressure in the range 10/sup -9/ &lt; P/sub O/sub 2// &lt; 1 atm at 1200/sup 0/C. The scope of the log D/sub Co/* vs log P/sub O/sub 2// plot changes from a value of about 1/4 at high P/sub O/sub 2// to about 1/5 at low P/sub O/sub 2// in agreement with the extensive measurements of Dieckmann. The isotope effect is independent of P/sub O/sub 2//, which suggests that diffusion by defect clusters, interstitial Co ions and impurity-induced defects is not important in the present measurements. Conductivity diffusion, stoichiometry, and isotope-effect results are consistent with diffusion by neutral, singly charged, and doubly charged vacancies; the relative contributions from the various vacancies varies with P/sub O/sub 2//.
Date: January 1, 1979
Creator: Peterson, N L & Chen, W K
Partner: UNT Libraries Government Documents Department

High-temperature Au implantation into Ni-Be and Ni-Si alloys

Description: Effects of implantation temperature and target composition on depth distribution of implanted species were investigated. Au[sup +] ions were implanted at 300 keV into polycrystalline Ni-Be and Ni-Si alloys between 25 and 700C to a dose of 10[sup 16] cm[sup [minus]2]. Depth distributions of Au were analyzed with RBS using He+ at both 1.7 and 3.0 MeV, and those of the other alloying elements by SIMS. Theoretical modeling of compositional redistribution during implantation at elevated temperatures was also carried out with the aid of a comprehensive kinetic model. The analysis indicated that below [approximately]250C, the primary controlling processes were preferential sputtering and displacement mixing, while between 250 and 600C radiation-induced segregation was dominant. Above 600C, thermal-diffusion effects were most important. Fitting of model calculations to experimental measurements provided values for various defect migration and formation parameters.
Date: December 1992
Creator: James, M. R.; Lam, N. Q.; Rehn, L. E.; Baldo, P. M.; Funk, L. & Stubbins, J. F.
Partner: UNT Libraries Government Documents Department

Radiation damage studies on natural and synthetic rock salt. [1 to 3 MeV electrons]

Description: Radiation damage studies are being made on natural rock salt from various localities, including potential repository sites and on synthetic melt-grown crystals. Sufficient information will be obtained to compute the radiation damage in repository salt at any point as a function of time, temperature, canister temperature and radiation levels, strain in the rock, salt, backfill materials, and other parameters. Most of the completed measurements have been made with unique equipment at BNL for making optical and other measurements on samples before, during, and after irradiation with 1- to 3-MeV electrons. Samples are irradiated in temperature-controlled chambers containing an inert exchange gas. Radiation damages on natural rock salts and synthetic melt-grown crystals, characterized by determining the radiation-induced F-center, colloid, and V-region absorption, are described in detail.
Date: January 1, 1980
Creator: Levy, P W & Swyler, K J
Partner: UNT Libraries Government Documents Department

Radiation induced amorphization in YBa2Cu3O7 and GdBa2Cu3O7 superconductors

Description: The response of YBa2Cu3O7 and GdBa2Cu3O7 high temperature superconductors to particle irradiation is examined. Both ion and electron irradiations have been shown to first produce an orthorhombic-to-tetragonal transformation at doses roughly a factor of 10 higher. Analysis of the displacement stoichiometry that results from 120, 300, and 1000 keV electron irradiations, 400 and 500 keV O irradiations, and 300 keV helium irradiations indicate that the orthorhombic-to-tetragonal transformation is driven by O atoms displacements either alone or in the presence of metal atom displacements and that the transformation to the amorphous phase is driven by displacements on the Y, Gd, or other rare earth atom site. 10 refs., 3 figs., 1 tab.
Date: January 1, 1988
Creator: Parkin, D.M. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

Zero-field spin relaxation of the positive muon in copper

Description: The spin relaxation of the ..mu../sup +/ in high purity single crystal and polycrystalline copper has been measured at temperatures between 0.5/sup 0/K and 5.2/sup 0/K by the zero-field ..mu../sup +/SR technique. In both types of sample the experiments show a temperature independent dipolar width ..delta../sub z/ = 0.389 +- 0.003 ..mu..s/sup -1/ and a hopping rate decreasing from approx. 0.5 ..mu..s/sup -1/ at 0.5/sup 0/K to approx. 0.05 ..mu..s/sup -1/ above 5/sup 0/K. This is the first direct proof of a dynamic effect in the low temperature ..mu../sup +/ spin relaxation in copper. The relationship between the zero-field and transverse-field dipolar widths is discussed, and the measured zero-field width is found to be approx. 10% larger than expected based on the known transverse-field widths. A new ..mu../sup +/SR spectrometer has been constructed and used in this work. The spectrometer and the associated beam lines and data acquisition facilities are discussed.
Date: July 1, 1982
Creator: Clawson, C.W.
Partner: UNT Libraries Government Documents Department

Radiation damage study on the lithium hydride SNAP shield

Description: Radiation damage may occur to the lithium hydride shields as a result of the reaction Li{sup 6}(n, {alpha})H{sup 3}. There is evidence in the literature indicating both the existence and absence of radiation damage to the SNAP shields. It is believed that there is a high probability that there will be damage and that it will adversely affect the properties of the shield. This damage may take the form of: (1) volume expansion of the hybrids, (2) void formation within the hybrids, and (3) gas pressure build-up in the shield container. Based upon the results of experiments with lithium fluoride, which may serve as a model for the hydride, there appears to be a threshold neutron dose which volume expansion effects can not be removed by annealing. Similarly, above the threshold dose, intercrystalline voids, formed as a result of radiation damage, appear to increase in size with increasing temperature. It has been established that at the SNAP shield operating conditions, essentially all of the hydrogen formed will recombine with free lithium. The helium atoms, however, remain trapped interstitially, in intercrystalline voids, or along subgrain boundaries. Appreciable amounts of helium gas are not released until the melting point of the hydride is approached. An insignificant portion of the hydrogen in the shield is lost by permeation of the stainless steel shield container at the SNAP 10 operating conditions. 23 refs.
Date: October 4, 1961
Creator: Doctor, R.D.
Partner: UNT Libraries Government Documents Department

The feasibility of welding of irradiated materials

Description: Helium was implanted into solution-annealed (SA) 316 stainless steel, 20% cold-worked (CW) 316 stainless steel and titanium-modified Primary Candidate Alloy (PCA) through tritium decay to levels ranging from 0.18 to 256 appm. Full penetration welds were then made on helium-doped materials using gas tungsten arc welding (GTAW) under fully constrained conditions. Intergranular heat-affected zone (HAZ) cracking was observed in all of the materials containing greater than 1 appm He. Electron microscopy showed that the HAZ cracking originated from the growth and coalescence of grain boundary (GB) helium bubbles. Bubble growth kinetics in the HAZ is explained by stress-enhanced diffusive cavity growth. Results suggest that the propensity for HAZ cracking can be reduced by the preexisting cold-worked structure and by finely-distributed MC precipitates that refine the distribution of helium bubbles and minimize the flow of vacancies in grain boundaries. 16 refs., 3 figs.
Date: January 1, 1989
Creator: Lin, H.T.; Chin, B.A. (Oak Ridge National Lab., TN (USA) & Auburn Univ., AL (USA). Dept. of Materials Engineering)
Partner: UNT Libraries Government Documents Department

Positron-annihilation 2D-ACAR studies of disordered and defected alloys

Description: Theoretical and experimental progess in connection with 2D-ACAR positron annihilation studies of ordered, disordered, and defected alloys is discussed. We present, in particular, some of the recent developments concerning the electronic structure of disordered alloys, and the work in the area of annihilation from positrons trapped at vacancy-type defects in metals and alloys. The electronic structure and properties of a number of compounds are also discussed briefly; we comment specifically on high T/sub c/ ceramic superconductors, Heusler alloys, and transition-metal aluminides. 58 refs., 116 figs.
Date: September 1, 1987
Creator: Bansil, A.; Prasad, R.; Smedskjaer, L.C.; Benedek, R. & Mijnarends, P.E.
Partner: UNT Libraries Government Documents Department

Nondestructive examination of deformed steel and nickel by positron annihilation

Description: Positron Annihilation (PA) Doppler broadening measurements were made on cold-rolled and fatigue cycled 316 stainless steel. PA measurements were made after isochronal annealing steps following deformation at 294 K of both 316 SS and high purity nickel. To understand the response of PA to microstructural changes, specimens were examined by transmission electron microscopy. It is concluded that in nickel both vacancies and dislocations produced by cold working can act as positron traps. In 316 SS, the PA response is principally due to vacancies, and only small effects can be attributed to trapping at dislocations.
Date: January 1, 1979
Creator: Gauster, W.B.; Wampler, W.R.; Jones, W.B. & Van den Avyle, J.A.
Partner: UNT Libraries Government Documents Department