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in subjects: "Vacancies"

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Secondary defects in quenched platinum

The structure of secondary defects in two different platinum purities quenched under ultra high vacuum, has been studied by transmission electron microscopy. Faulted loops on (100) planes have been observed in both materials. In the less pure platinum, Pt B (but purer in terms of carbon content), the defects were observed after quenching, whereas in the purest one, Pt A (but less pure in terms of carbon content), the defects were formed after a long annealing. The Burgers vector of the loops fo… more

Date: November 1, 1979

Creator: Perez, M.I.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Direct observations of the primary state of radiation damage of ion-irradiated tungsten and platinum

A brief summary was presented of all the Cornell work on the primary state of radiation damage in ion-irradiated tungsten and platinum. The primary research tool for all this research was the field-ion microscope (FIM); the FIM was ideally suited for this research because of its excellent atomic resolution and the ability to examine the interior of the specimens, as a result of the field-evaporation effect. This paper summarized, in outline form, the following items: (1) the principal experimen… more

Date: July 1, 1980

Creator: Seidman, D. N.; Current, M. I.; Pramanik, D. & Wei, C. Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Creep Rupture in the Presence of a Fast Neutron Flux

Possible mechanisms for creep rupture during irradiation are examined. Evidence that the rupture occurs by grain boundary sliding alone, or by vacancy condensation, is compared. It is observed that vacancy condensation is the more probable mechanism, and that this mechanism predicts a reduction in creep rupture life for metals exposed to a fast neutron flux (neglecting effects of radiation annealing). (T.F.H.)

Date: January 14, 1959

Creator: Gregory, D. P.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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RADIATION CREEP

Several theories of metal creep and radiation damage are studied, in order to determine whether creep rates under various conditions of irradiation can be predicted theoretically. It is found that if the creep is of the recovery type, and if the diffusion coefficient for radiationinduced vacancies is large enough, creep rates may be increased within a limited temperature range. Otherwise, radiation has no effect on creep rates. (T.F.H.)

Date: December 1, 1957

Creator: Gregory, D.P.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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DELAYED LUMINESCENCE IN ALKALI HALIDES UNDER F BLEACHING.

No Description Available.

Date: October 31, 1969

Creator: Manilerd, C & Kim, Y W

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Single atom sputtering events: direct observation of near-surface depleted zones in ion-irradiated tungsten

The three-dimensional spatial arrangement of vacancies contained in depleted zones (DZs), of ion-irradiated tungsten specimens, was determined with atomic resolution by the field-ion microscope (FIM) technique. These DZs were detected in the near-surface region of specimens which had been irradiated in situ at less than or equal to15 K with 20 keV W/sup +/, 30 keV W/sup +/, Kr/sup +/, Cu/sup +/, or Ar/sup +/ ions. The values of the ion dose employed were small (less than or equal to 10/sup 13/ … more

Date: March 1, 1980

Creator: Current, M. I.; Wei, C. Y. & Seidman, D. N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Ion-induced surface modification of alloys

In addition to the accumulation of the implanted species, a considerable number of processes can affect the composition of an alloy in the surface region during ion bombardment. Collisions of energetic ions with atoms of the alloy induce local rearrangement of atoms by displacements, replacement sequences and by spontaneous migration and recombination of defects within cascades. Point defects form clusters, voids, dislocation loops and networks. Preferential sputtering of elements changes the c… more

Date: November 1, 1983

Creator: Wiedersich, H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electron beam induced oxygen in YBa sub 2 Cu sub 3 O sub 7-x superconductors

Thin foils of bulk YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) superconductors were subjected to electron irradiation in a Transmission Electron Microscope (TEM). The resulting disordering of the oxygen atoms and vacancies in the Cu-O planes was monitored by measuring the splitting of the (110) diffraction spots in the (001) diffraction pattern. Samples were irradiated at 83K with 100, 150, 200 and 300kV electrons. The 100kV electrons did not cause any disordering, even after prolonged irradiation. Th… more

Date: January 1, 1989

Creator: Basu, S.N.; Roy, T.; Mitchell, T.E. & Nastasi, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Variable-energy positron studies of well-annealed single-crystal Cd samples from 35 to 450 K

Well-annealed Cd(001) and Cd(100) samples have been examined using a monoenergetic variable-energy positron beam (0.5 to 5.0 keV). The results are interpreted in the context of a one-dimensional-diffusion model which allows for annihilations as well as trapping at defects including thermally generated vacancies. The dependence on temperature of positron diffusion out of these samples was determined by the use of this model to interpret data taken between 35 and 450 K. The deduced positron diffu… more

Date: January 1, 1982

Creator: Lynn, K.G.; Goland, A.N.; Schultz, P.J.; Vehanen, A. & MacKenzie, I.K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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On the interpretation of lattice diffusion in magnesium oxide

No Description Available.

Date: January 1, 1974

Creator: Wuensch, B J

Item Type: Article

Partner: UNT Libraries Government Documents Department

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AN ESTIMATE OF THE EFFECT OF NEUTRON-ENERGY SPECTRUM ON RADIATION DAMAGE OF STEEL

The postulate that the average number of lattice displacements is directly proportional to the available energy is carried one step further; it is assumed that damage to steel (particularly in regard to brittle fracture) is proportional to the number of lattice vacancies that occur. The model, although crude, permits estimation of the relative damage resulting from differences in neutron spectra. The results can be used as a rough method of correcting damage data for the effect of the neutron-e… more

Date: July 27, 1962

Creator: Claiborne, H.C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Radiation damage measurements on rock salt and other minerals for waste disposal applications. Quarterly report, January 1, 1980-March 31, 1980

Different aspects of radiation damage in both synthetic NaCl crystals and various natural rock salt samples as well as granite, basalt and other minerals which will be important for radioactive waste disposal applications are being investigated. The principal means of measuring radiation damage is the determination of F-center concentrations, and the concentration and size of sodium metal colloid particles. Formation of these and other defects during irradiation and the annealing of defects and… more

Date: April 10, 1980

Creator: Swyler, K. J.; Loman, J. M.; Teutonico, L. J.; Elgort, G. E. & Levy, P. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Electron microscopy of ceramic superconductors

The critical current Jc is at least as important as Tc (transition temperature) for applications in superconducting materials. Jc is strongly dependent on microstructure and, in consequence, electron microscopy will continue to be important in the development of practical ceramic superconductors. We will review the progress that has been made over the past year or so in studying the superconductors by electron microscopy techniques of all kinds--conventional, high resolution, analytical, etc. A… more

Date: January 1, 1988

Creator: Mitchell, T.E. & Roy, T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The feasibility of welding of irradiated materials

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 micros… more

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)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Vacancies in thermal equilibrium in Nb

We have measured the diffusion of positrons in Nb(110) in the temperature range from 300K to 2450K utilizing a variable energy positron beam. The purpose was to study the vacancy formation. However, no significant sign of vacancy trapping was observed. This could be due to a high detrapping rate caused by a low positron binding energy or due to a high vacancy formation enthalpy H/sub IV//sup F/. The last possibility is consistent with recent studies of the vacancy migration and with calculation… more

Date: June 1, 1985

Creator: Nielsen, B.; Lynn, K.G.; Hurst, J.; Vehanen, A. & Schultz, P.J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Positron-annihilation studies of molybdenum irradiated by protons, neutrons, or electrons

Annealed molybdenum was irradiated at room temperature by energetic protons or neutrons and the fluence and recoil energy dependence of two traps was measured. Comparison of trapping rates with calculations of damage energy correlates high energy recoils with the short lifetime trap and low energy recoils with the longer lifetime.

Date: March 26, 1982

Creator: Howell, R.H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Evidence for shallow positron traps in a neutron-irradiated Al single crystal

Variable energy positrons have been used to determine the dependence on temperature of positron diffusion out of a neutron-irradiated single crystal of Al. The results are interpreted in the context of a one-dimensional diffusion model which includes bulk annihilations as well as trapping at voids and other microstructural defects in the bulk material by way of a removal rate kappa/sub eff/ of freely diffusing positrons. The data show a strongly negative dependence on temperature below 125/sup … more

Date: January 1, 1982

Creator: Schultz, P. J.; MacKenzie, I. K.; Lynn, K. G.; West, R. N. & Snead, C. L. Jr.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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

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 pr… more

Date: January 1, 1981

Creator: Levy, P.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Sputtering of tungsten: an atomic view of a near-surface depleted zone created by a single 30 keV /sup 63/Cu/sup +/ projectile. Report No. 4118

The vacancy structure of a near-surface depleted zone (DZ), created by a single 30 keV /sup 63/Cu/sup +/ ion in a tungsten field-ion microscope (FIM) specimen, was determined with atomic resolution. Both the irradiation and pulse field-evaporation experiments were performed in situ at less than or equal to 11 K, so that the observed vacancy structure was unaltered by the long-range migration of self-interstitial atoms. The following basic physical quantities were measured: (1) the number of vac… more

Date: January 1, 1979

Creator: Current, M. I. & Seidman, D. N.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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

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 … more

Date: September 1, 1987

Creator: Bansil, A.; Prasad, R.; Smedskjaer, L. C.; Benedek, R. & Mijnarends, P. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Thin film polycrystalline silicon solar cells. Quarterly report No. 1, October 1-December 31, 1979

The MoSi/sub 2/ separation layer growth rate has been studied as a function of time and temperature. The presence of small amounts of O/sub 2/ in the silicon deposition ambient were found to inhibit the growth rate of the MoSi/sub 2/ layer and also to affect the reliability of shear separation. Void formation in silicon at the Si-MoSi/sub 2/ interface, due predominantly to diffusion of silicon through the MoSi/sub 2/ layer was observed. This is believed to be responsible for shear separation oc… more

Date: January 1, 1979

Creator: Sarma, K. R.; Rice, M. J. & Legge, R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Recovery of neutron-irradiated high-purity Si

High-purity Si single crystals have been neutron irradiated at approx.100/sup 0/C to several fluences to 2 x 10/sup 20/ n/cm/sup 2/ (E > 1 MeV). Isochronal-annealing results using lifetime and Doppler broadening indicate a complex microstructural evolution of the Si with annealing temperature for the highest dose, going from divacancy, to quadrivacancy, to dislocation dominance of the trapping over four orders of magnitude in fluence. The lowest fluence features only divacancy effects.

Date: January 1, 1985

Creator: Snead, C. L. Jr. & Lynn, K. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Defects in metal crystals. Progress report, May 1, 1979-April 30, 1980

A broad investigation of the properties of crystal defects in metals and semiconductors was made. Attention during the past year has focused on fundamental properties of point defects (vacancies and self-interstitial atoms); aggregates of point defects (i.e., depleted zones); the range profiles of low-energy (< 1000 eV) implanted /sup 4/He and /sup 1/H in tungsten, the diffusive properties of /sup 4/He and /sup 1/H; the adsorption kinetics and sticking coefficient of hydrogen on tungsten; the i… more

Date: January 1, 1980

Creator: Seidman, D.N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Theoretical investigations of two Si-based spintronic materials

Two Si-based spintronic materials, a Mn-Si digital ferromagnetic heterostructure ({delta}-layer of Mn doped in Si) with defects and dilutely doped Mn{sub x}Si{sub 1-x} alloy are investigated using a density-functional based approach. We model the heterostructure and alloy with a supercell of 64 atoms and examine several configurations of the Mn atoms. We find that 25% substitutional defects without vacancies in the {delta} layer diminishes half metallicity of the DFH substantially. For the allo… more

Date: August 3, 2007

Creator: Fong, C Y; Snow, R; Shaughnessy, M; Pask, J E & Yang, L H

Item Type: Article

Partner: UNT Libraries Government Documents Department