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Description: Aluminum capsules with Al inserts and He atmospheres and containing 4 strips of Eu/sub 2/O/sub 3/-stainless steel were measured in the Reactivity Measurement Facility at MTR, both before and after irradiation. (T.R.H.)
Date: January 18, 1957
Creator: Henscheid, J.W. & Fast, E.
Partner: UNT Libraries Government Documents Department

Improvement of luminescent properties of thin-film phosphors by excimer laser processing

Description: Thin-films of europium doped yttrium oxide, (Y{sub 1{minus}x}Eu{sub x}){sub 2}O{sub 3}, were deposited on sapphire substrates by metallorganic chemical vapor deposition. The films, {approximately} 400 nm thick, were weakly luminescent in the as-deposited condition. A KrF laser was pulsed once on the surface of the films at a fluence level between 0.9--2.3 J/cm{sup 2}. One pulse was sufficient to melt the film, which increased the photoluminescent emission intensity. Melting of a rough surface resulted in smoothing of the surface. The highest energy pulse resulted in a decrease in luminous intensity, presumably due to material removal. Computational modeling of the laser melting and ablation process predicted that a significant fraction of the film is removed by ablation at the highest fluence levels.
Date: December 31, 1998
Creator: McKittrick, J.; Bacalski, C.F.; Hirata, G.A.; Sze, R.C.; Mourant, J.; Salazar, K.V. et al.
Partner: UNT Libraries Government Documents Department

Flux pinning forces in irradiated a-axis oriented EuBa{sub 2}Cu{sub 3}O{sub 7} films

Description: {alpha}-axis oriented EuBa{sub 2}Cu{sub 3}O{sub 7} films have been irradiated with high energy heavy ions in different configurations to study the possible pinning role of the artificial defects in this kind of samples. The original pinning limiting mechanism of the samples is not essentially altered what the irradiation is parallel to the CuO{sub 2} planes. However, when it is deviated from this direction, an increase in critical current density and a change in pinning force are observed when the magnetic field is parallel to the columnar defects at values around the matching field.
Date: October 12, 1999
Creator: Martin, J. I.; Gonzalez, E. M.; Kwok, W.-K & Vincent, J. L.
Partner: UNT Libraries Government Documents Department

Embedded Optical Sensors for Thermal Barrier Coatings

Description: In the second year of this program on developing embedded optical sensors for thermal barrier coatings, our research has focused three topics: (1) Eu{sup 3+} doping for temperature sensing, (2) the effect of long-term, high-temperature aging on the characteristics of the luminescence from the Eu{sup 3+} ions of 8YSZ materials, (3) construction of a fiber-optic based luminescence detector system. It has been demonstrated that the variation in luminescence lifetime with temperature is identical for electron-beam evaporated Eu-doped YSZ coatings as for bulk ceramics of the same composition. Experiments indicate that the luminescence lifetime method of measuring temperatures is sensitive up to 1150 C for both Eu-doped YSZ coatings and Eu-doped Gd{sub 2}Zr{sub 2}O{sub 7}. Furthermore, the technique is sensitive up to 1250 C for the composition Eu{sub 2}Zr{sub 2}O{sub 7}. The luminescence spectra Eu-doped YSZ are insensitive to long-term aging at high-temperatures, even to 195 hours at 1425 C, except for a small frequency shift that is probably too small in measure except with instruments of the highest spectral resolution. The temperature of 1425 C is much higher than present engines attain or even planned in the foreseeable future. Nevertheless, experiments are on-going to explore longer term exposures. A fiber-optic based luminescence system has been constructed in which the hottest section of fiber operates to at least 1250 C.
Date: November 9, 2005
Creator: Clarke, David R.
Partner: UNT Libraries Government Documents Department

Electronic, magnetic and structural properties of the RFe03 antiferromagnetic-perovskites at very high pressures

Description: At ambient pressure the orthorhombic perovskites R-orthoferrites (R {triple_bond}Lu, Eu, Y, Pr, and La) exhibit very large optical gaps. These large-gap Mott insulators in which the 3d{sup 5} high-spin ferric ions carry large local moments and magnetically order at T{sub N} > 600 K, undergo a sluggish structural first-order phase transition in the 30-50 GPa range, with the exception of the LuFeO{sub 3} which undergoes an isostructural volume reduction resulting from a high to low-spin crossover. High-pressure methods to 170 GPa using Moessbauer spectroscopy, resistance, and synchrotron-based XRD in diamond anvil cells were applied. Following the quasi-isostructural volume reduction (3-5%) the new phase the magnetic-ordering temperature is drastically reduced, to {approx}100 K, the direct and super-exchange interactions are drastically weakened, and the charge-transfer gap is substantially reduced. The high-pressure (HP) phases of the La and Pr oxides, at their inception, are composed of high- and low-spin Fe{sup 3+} magnetic sublattices, the abundance of the latter increasing with pressure but HP phases of the Eu, Y, and Lu oxides consist solely of low-spin Fe{sup 3+}. Resistance and Moessbauer studies in La and Pr orthoferrites reveal the onset of a metallic state with moments starting at P > 120 GPa. Based on the magnetic and electrical data of the latter species, a Mott phase diagram was established.
Date: January 1, 2002
Creator: Pasternak, M.; Xu, W. M.; Rozenberg, G. Kh. (Gregory Kh.) & Taylor, R. D. (R. Dean)
Partner: UNT Libraries Government Documents Department


Description: The composite plates of the absorber section consist of compacts of europium oxide-- stainless steel clad with stainless steel by hot roll-bonding. Specifications are given to cover materials, dimensional and finish requirements, tests for quallfication of absorber plate fabrication, the conformance of fabrication procedure, and the manufacturing procedures. Drawings are also included. (M.C.G.)
Date: May 13, 1960
Partner: UNT Libraries Government Documents Department


Description: Specifications were prepared for the control rod absorber sections for Core Il of Army Reactor PM-2A. The neutron absorber section was composed of composite plates welded into the form of a rectangular parallelepiped. The composite plates were made of compacts of europium oxide in a stainless steel matrix clad with stainless steel by hot-roll bonding. Specifications covering materials and processes are included in the repont along with fabrication qualification tests. (M.C.G.)
Date: May 13, 1960
Partner: UNT Libraries Government Documents Department


Description: An internal flux suppressor will be used for the APPR-1 Core II instead of the external suppressors that are employed in Core I. The reference design of the integral flux suppressor for Core II is as follows: materials Eu/sub 2/O/sub 3/ in stainless steel matrix; compositions 23.2 wt.% Eu/sub 2/O/sub 3/; and dimensions, 0.02 in. x 2.281 in. x 0.875 in. The survey on the cffectiveness of this referencc design has shown that thc peaking of the flux in the control rod fuel element tip is eliminated throughout the lifetime and therefore eliminating the possibility of local boiling in this region. (auth)
Date: April 10, 1958
Creator: Leibson, M.J.
Partner: UNT Libraries Government Documents Department


Description: The control rod fuel elements consist of 16 flat composite fuel plates joined to a pair of side plates to form an integral assembly with a nominal water gap spacing of 0.133 inches between fueL plates. The core section of the fuel plate contains an active fuel section and a flux suppressor section. The fuel section is composed of UO/sub 2/, B/sub 4/C, and type 304LB stainless steel. The suppressor section is composed of Eu/sub 2/O/sub 3/ and elemental stainless steel powder. The absorber section of the assembly contains four absorber plates. The core section of the absorber plate is cermet, composed of Eu/sub 2/O/sub 3/ dispersed in stainless steel. (W.L.H.)
Date: December 30, 1958
Creator: Edgar, E.C. & Robertson, R.D.
Partner: UNT Libraries Government Documents Department

Characterization of photoluminescent (Y{sub 1{minus}x}Eu{sub x}){sub 2}O{sub 3} thin-films prepared by metallorganic chemical vapor deposition

Description: Europium doped yttrium oxide, (Y{sub 1{minus}x}Eu{sub x}){sub 2}O{sub 3}, thin-films were deposited on silicon and sapphire substrates by metallorganic chemical vapor deposition (MOCVD). The films were grown in a MOCVD chamber reacting yttrium and europium tris(2,2,6,6-tetramethyl-3,5,-heptanedionates) precursors in an oxygen atmosphere at low pressures (5 Torr) and low substrate temperatures (500--700 C). The films deposited at 500 C were flat and composed of nanocrystalline regions of cubic Y{sub 2}O{sub 3}, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600 C developed from the flat, nanocrystalline morphology into a plate-like growth morphology oriented in the [111] with increasing deposition time. Monoclinic Y{sub 2}O{sub 3}:Eu{sup 3+} was observed in x-ray diffraction for deposition temperatures {ge}600 C on both (111) Si and (001) sapphire substrates. This was also confirmed by the photoluminescent emission spectra.
Date: December 1, 1998
Creator: McKittrick, J.; Bacalski, C. F.; Hirata, G. A.; Hubbard, K. M.; Pattillo, S. G.; Salazar, K. V. et al.
Partner: UNT Libraries Government Documents Department

Spin Freezing and Recovery of Sublattice Magnetization in Lightly Doped Lanthanum Cuprate

Description: {sup 139}La NQR studies in lightly doped La{sub 2}Cu{sub 1-x}Li{sub x}O{sub 4} and La{sub 1.8-x}Eu{sub 0.2}Sr{sub x}CuO{sub 4} are reviewed. A strong enhancement of the {sup 139}La relaxation rate with a peak accompanied by a sudden increase of the local field at low T has been observed similarly to La{sub 2-x}Sr{sub x}CuO{sub 4}. The anomalous magnetic properties are discussed in the light of the microscopic segregation of doped holes into hole-rich domain walls separating undoped AF domains.
Date: October 24, 1998
Creator: Suh, B. J.; Hammel, P. C.; Sarrao, J. L.; Thompson, J. D.; Fisk, Z.; Hucker, M. et al.
Partner: UNT Libraries Government Documents Department

Reactor Physics Studies of Reduced-Tantaulum-Content Control and Safety Elements for the High Flux Isotope Reactor

Description: Some of the unirradiated High Flux Isotope Reactor (HFIR) control elements discharged during the late 1990s were observed to have cladding damage--local swelling or blistering. The cladding damage was limited to the tantalum/europium interface of the element and is thought to result from interaction of hydrogen and europium to form a compound of lower density than europium oxide, thus leading to a ''blistering'' of the control plate cladding. Reducing the tantalum loading in the control plates should help preclude this phenomena. The impact of the change to the control plates on the operation of the reactor was assessed. Regarding nominal, steady-state reactor operation, the impact of the change in the power distribution in the core due to reduced tantalum content was calculated and found to be insignificant. The magnitude and impact of the change in differential control element worth was calculated, and the differential worths of reduced tantalum elements vs the current elements from equivalent-burnup critical configurations were determined to be unchanged within the accuracy of the computational method and relevant experimental measurements. The location of the critical control elements symmetric positions for reduced tantalum elements was found to be 1/3 in. less withdrawn relative to existing control elements regardless of the value of fuel cycle burnup (time in the fuel cycle). The magnitude and impact of the change in the shutdown margin (integral rod worth) was assessed and found to be unchanged. Differential safety element worth values for the reduced-tantalum-content elements were calculated for postulated accident conditions and were found to be greater than values currently assumed in HFIR safety analyses.
Date: November 1, 2003
Creator: Primm, R.T., III
Partner: UNT Libraries Government Documents Department

Observations of CEF-split intermultiplet transitions in optically opaque EuBa{sub 2}Cu{sub 3}O{sub 7} using inelastic neutron scattering

Description: Inelastic neutron scattering (INS) results on the intermultiplet transitions J=0 {yields} 1 and J=l {yields} 2 in optically opaque EuBa{sub 2}Cu{sub 3}O{sub 7} are reported. Whereas these multiplets are split by the crystalline electric field (CEF), their low J values are influenced to first order only by the 2 second-order (J=l) and additional fourth-order (J=2) CEF parameters. B{sub 0}{sup 2}, B{sub 2}{sup 2} and the spin-orbit coupling parameter were obtained by fitting the splitting of the J=1 multiplet and the energy separation between the J=0 and 1 multiplets. The J=0 to 1 splitting observed here is smaller than previously seen by optical spectroscopic studies on a variety of transparent, ionic compounds, necessitating fitting of the free-ion parameter. Additional spectroscopic information on the J=2 multiplet indicates that additional fitting of free ion parameters must be included to adequately model the observed low energy separation between the two lowest J-multiplets. Preliminary calculation on the Q-dependence of the CEF split J=0 to 1 transitions and the comparison with observations are presented.
Date: February 1, 1995
Creator: Staub, U.; Soderholm, L.; Osborn, R.; Balcar, E. & Trunov, V.
Partner: UNT Libraries Government Documents Department

Effects of temperature and microstructure on the elastic properties of selected Eu$sub 2$O$sub 3$-HfO$sub 2$ compositions

Description: Europium oxide is presently being tested for use as the control material in future nuclear power reactors. Elastic properties of europia and selected europia-rich compositions of the europia-hafnia system were investigated. The sonic technique was employed to measure elastic moduli from room temperature to 1500$sup 0$C. Sintered monoclinic europia specimens were found to have uncommonly low room temperature moduli values and to exhibit hysteresis between heating and cooling curves because of the presence of microcracks caused by thermal expansion anisotropy. Fine grained hot pressed europia as well as sintered specimens that contained at least 6 mole percent hafnia did not exhibit these characteristics. Photomicrographs revealed that grain growth suppression was produced by and related to the amount of hafnia introduced. Hysteresis loops in the moduli versus temperature measurements were exhibited only by those specimens for which the average grain size was in excess of a critical value of 8 $mu$m. Dilatometer measurements indicated that thermal expansion was relatively constant over the compositional range of interest. (auth)
Date: October 1, 1975
Creator: Suchomel, R.R.
Partner: UNT Libraries Government Documents Department