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Science & Technology Review April/May 2010

Description: This month's issue has the following articles: (1) Fifty Years of Stellar Laser Research - Commentary by Edward I. Moses; (2) A Stellar Performance - By combining computational models with test shot data, scientists at the National Ignition Facility have demonstrated that the laser is spot-on for ignition; (3) Extracting More Power from the Wind - Researchers are investigating how atmospheric turbulence affects power production from wind turbines; (4) Date for a Heart Cell - Carbon-14 dating reveals that a significant number of heart muscle cells are regenerated over the course of our lives; and (5) Unique Marriage of Biology and Semiconductors - A new device featuring a layer of fat surrounding a thin silicon wire takes advantage of the communication properties of both biomolecules and semiconductors.
Date: March 8, 2010
Creator: Blobaum, K M
Partner: UNT Libraries Government Documents Department

Science and Technology Review December 2010

Description: This month's issue has the following articles: (1) More Insight to Better Understand Climate Change - Commentary by Tomas Diaz de la Rubia; (2) Strengthening Our Understanding of Climate Change - Researchers at the Center for Accelerator Mass Spectrometry are working to better understand climate variation and sharpen the accuracy of predictive models; (3) Precision Diagnostics Tell All - The National Ignition Facility relies on sophisticated diagnostic instruments for measuring the key physical processes that occur in high-energy-density experiments; (4) Quick Detection of Pathogens by the Thousands - Livermore scientists have developed a device that can simultaneously identify thousands of viruses and bacteria within 24 hours; and (5) Carbon Dioxide into the Briny Deep - A proposed technique for burying carbon dioxide underground could help mitigate the effects of this greenhouse gas while producing freshwater.
Date: October 29, 2010
Creator: Blobaum, K M
Partner: UNT Libraries Government Documents Department

Science and Technology Review July/August 2010

Description: This issue has the following articles: (1) Deterrence with a Minimum Nuclear Stockpile - Commentary by Bruce T. Goodwin; (2) Enhancing Confidence in the Nation's Nuclear Stockpile - Livermore experts are participating in a national effort aimed at predicting how nuclear weapon materials and systems will likely change over time; (3) Narrowing Uncertainties - For climate modeling and many other fields, understanding uncertainty, or margin of error, is critical; (4) Insight into a Deadly Disease - Laboratory experiments reveal the pathogenesis of tularemia in host cells, bringing scientists closer to developing a vaccine for this debilitating disease. (5) Return to Rongelap - On the Rongelap Atoll, Livermore scientists are working to minimize radiological exposure for natives now living on or wishing to return to the islands.
Date: May 27, 2010
Creator: Blobaum, K M
Partner: UNT Libraries Government Documents Department

Ambient-temperature Conditioning as a Probe of Double-C Transformation Mechanisms in Pu-2.0 at. % Ga

Description: The gallium-stabilized Pu-2.0 at. % Ga alloy undergoes a partial or incomplete low-temperature martensitic transformation from the metastable {delta} phase to the gallium-containing, monoclinic {alpha}{prime} phase near -100 C. This transformation has been shown to occur isothermally and it displays anomalous double-C kinetics in a time-temperature-transformation (TTT) diagram, where two nose temperatures anchoring an upper- and lower-C describe minima in the time for the initiation of transformation. The underlying mechanisms responsible for the double-C behavior are currently unresolved, although recent experiments suggest that a conditioning treatment--wherein, following an anneal at 375 C, the sample is held at a sub-anneal temperature for a period of time--significantly influences the upper-C of the TTT diagram. As such, elucidating the effects of the conditioning treatment upon the {delta} {yields} {alpha}{prime} transformation can provide valuable insights into the fundamental mechanisms governing the double-C kinetics of the transition. Following a high-temperature anneal, a differential scanning calorimeter (DSC) was used to establish an optimal conditioning curve that depicts the amount of {alpha}{prime} formed during the transformation as a function of conditioning temperature for a specified time. With the optimal conditioning curve as a baseline, the DSC was used to explore the circumstances under which the effects of the conditioning treatment were destroyed, resulting in little or no transformation.
Date: April 2, 2008
Creator: Jeffries, J R; Blobaum, K M; Wall, M A & Schwartz, A J
Partner: UNT Libraries Government Documents Department

Transmission Electron Microscopy Characterization of Helium Bubbles in Aged Plutonium

Description: The self-irradiation damage generated by alpha decay of plutonium results in the formation of lattice defects, helium, and uranium atoms. Over time, microstructural evolution resulting from the self-irradiation may influence the physical and mechanical properties of the material. In order to assess microstructural changes, we have developed and applied procedures for the specimen preparation, handling, and transmission electron microscopy characterization of Pu alloys. These transmission electron microscopy investigations of Pu-Ga alloys ranging in age up to 42-years old reveal the presence of nanometer-sized helium bubbles. The number density of bubbles and the average size have been determined for eight different aged materials.
Date: November 2, 2004
Creator: Schwartz, A J; Wall, M A; Zocco, T G & Blobaum, K M
Partner: UNT Libraries Government Documents Department

ISOTHERMAL (DELTA)/(ALPHA-PRIME) TRANSFORMATION AND TTT DIAGRAM IN A PLUTONIUM GALLIUM ALLOY

Description: Differential scanning calorimetry (DSC) is used as an alternative approach to determining the tine-temperature-transformation (TTT) diagram for the martensitic delta to alpha-prime transformation in a Pu-2.0 at% Ga alloy. Previous work suggests that the TTT diagram for a similar alloy exhibits an unusual double-C curve for isothermal holds of less than 100 minutes. Here, we extend this diagram to 18 hours, and confirm the double-C curve behavior. When the sample is cooled prior to the isothermal holds, the delta to alpha-prime transformation is observed as several overlapping exothermic peaks. These peaks are very reproducible, and they are believed to be the result of different kinds of delta to alpha-prime martensitic transformation. This may be due to the presence of different nucleation sites and/or different morphologies.
Date: November 11, 2005
Creator: Oudot, B P; Blobaum, K M; Wall, M A & Schwartz, A J
Partner: UNT Libraries Government Documents Department

Nucleation and growth of the Alpha-Prime Phase martensitic phase in Pu-Ga Alloys

Description: In a Pu-2.0 at% Ga alloy, it is observed experimentally that the amount of the martensitic alpha-prime product formed upon cooling the metastable delta phase below the martensite burst temperature (M{sub b}) is a function of the holding temperature and holding time of a prior conditioning (''annealing'') treatment. Before subjecting a sample to a cooling and heating cycle to form and revert the alpha-prime phase, it was first homogenized for 8 hours at 375 C to remove any microstructural memory of prior transformations. Subsequently, conditioning was carried out in a differential scanning calorimeter apparatus at temperatures in the range between -50 C and 370 C for periods of up to 70 hours to determine the holding time and temperature that produced the largest volume fraction of alpha-prime upon subsequent cooling. Using transformation peak areas (i.e., the heats of transformation) as a measure of the amount of alpha-prime formed, the largest amount of alpha-prime was obtained following holding at 25 C for at prime least 6 hours. Additional time at 25 C, up to 70 hours, did not increase the amount of subsequent alpha-prime formation. At 25 C, the Pu-2.0 at% Ga alloy is below the eutectoid transformation temperature in the phase diagram and the expected equilibrium phases are {alpha} and Pu{sub 3}Ga, although a complete eutectoid decomposition of delta to these phases is expected to be extremely slow. It is proposed here that the influence of the conditioning treatment can be attributed to the activation of alpha-phase embryos in the matrix as a beginning step toward the eutectoid decomposition, and we discuss the effects of spontaneous self-irradiation accompanying the Pu radioactive decay on the activation process. Subsequently, upon cooling, certain embryos appear to be active as sites for the burst growth of martensitic alpha-prime particles, and their amount, distribution, and ...
Date: February 9, 2005
Creator: Blobaum, K M; Krenn, C R; Wall, M A; Massalski, T B & Schwartz, A J
Partner: UNT Libraries Government Documents Department

Probing the isothermal (delta)->(alpha)' martensitic transformation in Pu-Ga with in situ x-ray diffraction

Description: The time-temperature-transformation (TTT) curve for the {delta} {yields} {alpha}{prime} isothermal martensitic transformation in a Pu-1.9 at. % Ga alloy is peculiar because it is reported to have a double-C curve. Recent work suggests that an ambient temperature conditioning treatment enables the lower-C curve. However, the mechanisms responsible for the double-C are still not fully understood. When the {delta} {yields} {alpha}{prime} transformation is induced by pressure, an intermediate {gamma}{prime} phase is observed in some alloys. It has been suggested that transformation at upper-C temperatures may proceed via this intermediate phase, while lower-C transformation progresses directly from {delta} to {alpha}{prime}. To investigate the possibility of thermally induced transformation via the intermediate {gamma}{prime} phase, in situ x-ray diffraction at the Advanced Photon Source was performed. Using transmission x-ray diffraction, the {delta} {yields} {alpha}{prime} transformation was observed in samples as thin at 30 {micro}m as a function of time and temperature. The intermediate {gamma}{prime} phase was not observed at -120 C (upper-C curve) or -155 C (lower-C curve). Results indicate that the bulk of the {alpha}{prime} phase forms relatively rapidly at -120 C and -155 C.
Date: March 11, 2010
Creator: Jeffries, J R; Blobaum, K M; Schwartz, A J; Cynn, H; Yang, W & Evans, W J
Partner: UNT Libraries Government Documents Department

Isothermal Martensitic and Pressure-Induced ? to ?? Phase Transformations in a Pu-Ga Alloy

Description: A Pu-2 at.% Ga alloy specimen is slowly compressed to {approx}1 GPa in a large volume moissanite anvil cell to induce the face-centered cubic {delta} to simple monoclinic {alpha}{prime} phase transformation. Optical microscopy, x-ray diffraction, and transmission electron microscopy of the specimen recovered to ambient pressure reveal that the vast majority of the microstructure consists of the {alpha}{prime} phase with grain sizes ranging from 10 nm to several hundred nm, with the remainder being {delta} phase dispersed between the {alpha}{prime} grains. This morphology is in contrast to the transformation product of the low-temperature isothermal martensite in which the lath-shaped {alpha}{prime} particles are {approx}20 {micro}m by 2 {micro}m.
Date: September 10, 2007
Creator: Schwartz, A. J.; Wall, M. A.; Farber, D. L.; Moore, K. T. & Blobaum, K. M.
Partner: UNT Libraries Government Documents Department

Isothermal Martensitic and Pressure-Induced Delta to Alpha-Prime Phase Transformations in a Pu-Ga Alloy

Description: A well-homogenized Pu-2 at.% Ga alloy can be retained in the metastable face-centered cubic {delta} phase at room temperature. Ultimately, this metastable {delta} phase will decompose via a eutectoid transformation to the thermodynamically stable monoclinic {alpha} phase and the intermetallic compound Pu{sub 3}Ga over a period of approximately 10,000 years [1]. In addition, these low solute-containing {delta}-phase Pu alloys are metastable with respect to an isothermal martensitic phase transformation to the {alpha}{prime} phase during low temperature excursions [2, 3] and are also metastable with respect to a {delta} {yields} {alpha}{prime} phase transformation with increases in pressure [3-5]. The low temperature {delta} {yields} {alpha}{prime} isothermal martensitic phase transformation in the Pu-2 at.% Ga alloy only goes to {approx}25% completion with the resultant {approx}20 {micro}m long by 2 {micro}m wide lath-shaped {alpha}{prime} particles dispersed within the {delta} matrix. In recently reported studies, Faure et al. [4] have observed a {delta} {yields} {gamma} {yields} {alpha}{prime} pressure-induced phase transformation sequence during a diamond anvil cell investigation and, based on x-ray diffraction and density and compressibility experiments, Harbur [5] has concluded that both {alpha}{prime} and an amorphous phase are present in samples that were pressurized and recovered. In this work, a large volume moissanite anvil cell is constructed to permit the pressurization and recovery of specimens of a size suitable for TEM and electron diffraction studies. The cell, shown in Fig. 1, has an overall diameter of 101.6 mm, a moissanite anvil diameter of 9.00 mm, a culet size of 3 mm, and a spring steel gasket 0.5 mm thick with a hole diameter of 2.5 mm. A 2.3 mm diameter by 100 {micro}m thick sample of {delta}-phase Pu-2 at.% Ga is compressed at a rate of approximately 0.05 GPa/minute to {approx}1 GPa to induce the phase transformation to {alpha}{prime}. Optical microscopy of the recovered ...
Date: January 18, 2008
Creator: Schwartz, A J; Wall, M A; Farber, D L; Moore, K T & Blobaum, K M
Partner: UNT Libraries Government Documents Department

Evidence for the Spectroscopic Signature of Aging in (delta)-Pu(Ga)

Description: Plutonium, because of its radioactive nature, ages from the 'inside out' by means of self-irradiation damage and thus produces nanoscale internal defects. The self-irradiation induced defects come in the form of Frenkel-type defects (vacancies and self-interstitial atoms), helium in-growth, and defect clusters. At present there are neither experimental nor theoretical models describing the changes in the electronic structure caused by the aging in Pu. This fact appears to be associated primarily with the absence of reasonably convincing spectroscopic evidence of the changes. This paper demonstrates that Resonant Photoemission, a variant of Photoelectron Spectroscopy, has strong sensitivity to aging of Pu samples. The spectroscopic results are correlated with an extra-atomic screening model [1], and are shown to be the fingerprint of mesoscopic or nanoscale internal damage in the Pu physical structure. This means that a spectroscopic signature of internal damage due to aging in Pu has been established.
Date: November 23, 2005
Creator: Chung, B W; Schwartz, A J; Ebbinghaus, B B; Fluss, M J; Haslam, J J; Blobaum, K M et al.
Partner: UNT Libraries Government Documents Department

Evidence of Transformation Bursts During Thermal Cycling of a Pu-Ga Alloy

Description: The thermodynamics and kinetics of the fcc (delta) to monoclinic (alpha-prime) phase transformation and its reversion in a plutonium-gallium alloy have been studied using differential scanning calorimetry, resistometry, and dilatometry. Under ambient conditions, the delta phase is metastable in a Pu-2.0 at% Ga alloy. Thermal cycling to below the ambient temperature results in a partial transformation to the alpha-prime phase; this transformation is composition-invariant and exhibits martensitic behavior. Because this transformation results in an unusually invariant large 25% volume contraction that cannot be fully accommodated by purely elastic adjustments, the transformation mode is expected to involve burst formation of individual alpha-prime particles. However, upon cooling, these individual bursts were not resolved by the above techniques, although signals corresponding to the overall accumulation of many alpha-prime particles were observed. On the other hand, upon heating, signals from differential scanning calorimetry, resistometry, and dilatometry showed a series of discrete changes occurring in periodic increments beginning at approximately 32 C. These features correspond to the cooperative reversion of many alpha-prime particles to the delta phase; they appear to be the result of an interplay between the autocatalytically driven reversion of a cascade of individual martensite units, and self-quenching caused by small changes of temperature and/or stress accompanying each individual transformation burst. The heat of the delta/alpha-prime transformation is estimated to be about + 4 kJ/mole.
Date: February 9, 2005
Creator: Blobaum, K M; Krenn, C R; Mitchell, J N; Haslam, J J; Wall, M A; Massalski, T B et al.
Partner: UNT Libraries Government Documents Department

Spectroscopic Signature of Aging in (delta)-Pu(Ga)

Description: Resonant Photoemission, a variant of Photoelectron Spectroscopy, has been demonstrated to have sensitivity to aging of Pu samples. The spectroscopic results are correlated with resistivity measurements and are shown to be the fingerprint of mesoscopic or nanoscale internal damage in the Pu physical structure. This means that a spectroscopic signature of internal damage due to aging in Pu has been established.
Date: April 15, 2005
Creator: Chung, B W; Schwartz, A J; Ebbinghaus, B B; Fluss, M J; Haslam, J J; Blobaum, K M et al.
Partner: UNT Libraries Government Documents Department

L1 Report for the Enhanced Surveillance Campaign Experimental Benchmarking of Pu Electronic Structure

Description: The objective of this work is to develop and/or apply advanced diagnostics to the understanding of aging of Pu. Advanced characterization techniques such as photoelectron and x-ray absorption spectroscopy will provide fundamental data on the electronic structure of Pu phases. These data are crucial for the validation of the electronic structure methods. The fundamental goal of this project is to narrow the parameter space for the theoretical modeling of Pu aging. The short-term goal is to perform experiments to validate electronic structure calculations of Pu. The long-term goal is to determine the effects of aging upon the electronic structure of Pu. Many of the input parameters for aging models are not directly measurable. These parameters will need to be calculated or estimated. Thus a First Principles-Approach Theory is needed, but it is unclear what terms are important in the Hamiltonian (H{Psi} = E{Psi}). Therefore, experimental data concerning the 5f electronic structure are needed, to determine which terms in the Hamiltonian are important. The data obtained in this task are crucial for reducing the uncertainty of Task LL-01-developed models and predictions. The data impact the validation of electronic structure methods, the calculation of defect properties, the evaluation of helium diffusion, and the validation of void nucleation models. The importance of these activities increases if difficulties develop with the accelerating aging alloy approach.
Date: January 30, 2006
Creator: Tobin, J G; Chung, B W; Moore, K T; Yu, S; Schwartz, A J; Wall, M A et al.
Partner: UNT Libraries Government Documents Department