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Dynamic shock studies of vanadium

Description: Using gas-gun loading techniques and velocity interferometric techniques, time-resolved wave profiles have been obtained in vanadium over the stress range of 2.9 to 9.7 GPa. The risetime data indicate steepened shock structures with increasing shock amplitude. However, unlike aluminum, finite risetimes are determined even at 9.7 GPa, indicating a large effective viscosity for the material. The dynamic yield strength measured at the Hugoniot elastic limit is 0.8 GPa and is approximately twice the static yield strength. Material softening is evidenced through measurements of shock velocity and yield strength determinations in the shocked state. The yield strength of the material upon release from the shocked state is estimated to be approx.0.43 GPa and is comparable to the static yield strength. Strain-rate dependent processes may be responsible for a higher elastic shear stress sustained before relaxation to an equilibrium value. The primary mode of deformation in shocked vanadium appears to be cross slip, resulting in dislocation tangles. Deformation twins are also observed in shock-recovered specimens with an increasing number with increased shock stress. The thermal diffusivity for vanadium is low, and the shear-strength loss observed in this material is consistent with the strength loss observed for other materials which also have low thermal diffusivities. It is conceivable that the loss of shear strength may be due to long thermal recovery times resulting from inhomogeneous deformation process.
Date: January 1, 1985
Creator: Chhabildas, L.C. & Hills, C.R.
Partner: UNT Libraries Government Documents Department

Migration of cesium-137 through a solid core of Magenta dolomite taken from th Rustler Formation in Southeastern New Mexico

Description: A column-flow cesium migration experiment has been conducted in support of the safety assessment program for the Waste Isolation Pilot Plant (WIPP) in Southeastern New Mexico. The column was a monolithic cylinder of Magenta dolomite obtained from a core sample drilled near the proposed WIPP site. The fluid was a Magenta equilibrated de-ionized water solution that had been doped with 0.001 ppM of /sup 137/Cs. The experiment ran continuously for an 18 month period at flow rates comparable to those measured for natural groundwater at the site. After flowing for 18 months, the apparatus was disassembled and the dolomite column examined for cesium distribution. Cross sectional radiographs of the sample showed that most of the cesium had penetrated only 0.4 cm into the solid Magenta column with a well defined wave front. On the other hand, trace quantities (2 x 10/sup -7/ ppM) of /sup 137/Cs were detected in effluent samples collected during the experiment. The distribution coefficient (120 ml/gm) calculated (assuming porous flow) from the average depth of cesium penetration (0.3 cm) is considerably less than the value obtained from a batch equilibration measurement made on the same system (650 ml/gm), indicating that cesium will migrate through Magenta rock at a faster rate than batch equilibration value predicts. Transmission electron microscope analysis of a piece of Magenta dolomite from the same core that had been soaked in 1 molar CsCl solution indicated that the cesium was preferentially sorbed on a montmorillonite clay phase that was inhomogeneously dispersed throughout the sample. These results indicate that if groundwater travels through Magenta rock the dissolved cesium may be retarded by the clay content of the rock.
Date: March 1, 1981
Creator: Lynch, A. W.; Dosch, R. G. & Hills, C. R.
Partner: UNT Libraries Government Documents Department

Application of MCNP{trademark} to computed tomography in medicine

Description: The MCNP{trademark} code has been used to simulate CT scans of the MIRD human phantom. In addition. an actual CT scan of a patient was used to create an MCNP geometry, and this geometry was computationally ``CT scanned`` using MCNP to reconstruct CT images. The results show that MCNP can be used to model the human body based on data obtained from CT scans and to simulate CT scans that are based on these or other models.
Date: March 1, 1996
Creator: Brockhoff, R.C.; Estes, G.P.; Hills, C.R.; Demarco, J.J. & Solberg, T.D.
Partner: UNT Libraries Government Documents Department

Properties of chemical vapor infiltration diamond deposited in a diamond powder matrix

Description: Densifying non-mined diamond powder precursors with diamond produced by chemical vapor infiltration (CVI) is an attractive approach for forming thick diamond deposits that avoids many potential manufacturability problems associated with predominantly chemical vapor deposition (CVD) processes. The authors have developed two techniques: electrophoretic deposition and screen printing, to form nonmined diamond powder precursors on substrates. They then densify these precursors in a hot filament assisted reactor. Analysis indicated that a hot filament assisted chemical vapor infiltration process forms intergranular diamond deposits with properties that are to some degree different from predominantly hot-filament-assisted CVD material.
Date: December 31, 1993
Creator: Panitz, J. K. G.; Tallant, D. R.; Hills, C. R. & Staley, D. J.
Partner: UNT Libraries Government Documents Department

Ion-implanted hydrogen in gallium nitride

Description: Hydrogen was ion-implanted into GaN at concentrations ranging over two orders of magnitude, and its states and microstructural effects during annealing up to 1000 C were characterized by nuclear-reaction profiling, ion-channeling analysis, transmission electron microscopy, and infrared spectroscopy of H vibrational modes.
Date: August 1, 1998
Creator: Myers, S.M.; Han, J.; Headley, T.J.; Hills, C.R.; Petersen, G.A.; Seager, C.H. et al.
Partner: UNT Libraries Government Documents Department