Waste Volume Reduction Using surface Characterization and Decontamination Laser Ablation

The Department of Energy's nuclear complex contains a significant amount of contaminated concrete containing radionuclides only in the near-surface region, typically a few millimeters deep. DOE will realize significant savings in decontamination costs and waste volume if the contaminated surface is removed from the clean bulk. Laser ablation is attractive because it adds no additional waste, offers fine control over the amount of material removed, can work on cracked, curved or irregular surfaces, can potentially be instrumented for real-time analysis, and can be used on virtually any material surface. The objectives of this research are to determine the mechanism and efficacy of laser ablation in removing contaminated surface layers, to understand the chemistry of contaminated concrete surfaces, and to chemically and physically characterize the captured ablation effluent which would become the stored waste. While the focus of this project is on concrete, the technology should be applicable to any surface requiring removal

Waste Volume Reduction Using Surface Characterization and Decontamination By Laser Ablation

The U.S. Department of Energy's nuclear complex, a nation-wide system of facilities for research and production of nuclear materials and weapons, contains large amounts of radioactively contaminated concrete[1]. This material must be disposed of prior to the decommissioning of the various sites. Often the radioactive contaminants in concrete occupy only the surface and near-surface ({approx}3-6 mm deep) regions of the material. Since many of the structures such as walls and floors are 30 cm or more thick, it makes environmental and economic sense to try to remove and store only the thin contaminated layer rather than to treat the entire structure as waste. Current mechanical removal methods, known as scabbling, are slow and labor intensive, suffer from dust control problems, and expose workers to radiation fields. Improved removal methods are thus in demand[2-5]. Prior to decontamination, the surface must be characterized to determine the types and amounts of contaminants present i n order to decide on an appropriate cleaning strategy. Contamination occurs via exposure to air and water-borne radionuclides and by neutron activation. The radionuclides of greatest concern are (in order of abundance) [1]: 137Cs & 134Cs, 238U, 60Co, and 90Sr, followed by 3H, radioactive iodine, and a variety of Eu isotopes and transuranics. A system capable of on- line analysis is valuable since operators can determine the type of contaminants in real time and make more efficient use of costly sampling and characterization techniques. Likewise, the removed waste itself must be analyzed to insure that proper storage and monitoring techniques are used. The chemical speciation of radionuclides in concrete is largely unknown. Concrete is a complex material comprising many distinct chemical and physical phases on a variety of size scales[6-8]. Most studies of radionuclides in cements and concrete are for the most part restricted to phenomenological treatments of diffusion of ion s, particularly Cs, in and out of model waste forms and engineered barriers[9-21]. Few studies exist on the chemical speciation of the contaminants themselves in concrete [22-25]. For example, the extent to which various contaminants react with the cement and various aggregate particles is currently unknown, as is the role of the high pH of the cement pore water on ion partitioning and chemical speciation. DOE has designated understanding the chemical nature of the contaminants as important in the rational design of characterization, decontamination, and waste handling strategies[26, 27]. We have investigated laser ablation as a means of concrete surface removal[28-31]. Lasers are attractive since the power can be delivered remotely via articulated mirrors or fiber optic cables and the ablation head can be manipulated by robots, thus avoiding exposing workers and the laser system to the radiation field. In addition, lasers can be instrumented with spectrometers or effluent sampling devices to provide for on-line analysis. In contrast to mechanical scabbling systems, laser beams can penetrate cracks or follow very rough or irregularly shaped surfaces. Finally, a laser ablation system produces the smallest possible waste stream since no cleaning agents such as detergents or grit (from grit blasting systems) are mixed with the effluent

A particle-on-a-sphere model for C60

A perimeter model for the [pi] electrons of C60 is developed and implemented within the independent particle approximation. Physically, the model gives the energy levels of a particle on a sphere pertubed by the icosahedral potential set up by the 60 carbon atomic cores. Computational techniques are adapted from well known crystal field formalisms. The molecular orbitals are represented by linear combinations of spherical harmonics. One or two adjustable parameters are used to give reasonable agreement with the observed UV-visible spectrum and with semi-empirical and ab initio calculations at a similar level of approximation. A closed-shell ground state, appreciable HOMO-LUMO gap, and electric dipole forbidden HOMO-LUMO transition are predictedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30843/1/0000505.pd

Correlated Strontium and Barium Isotopic Compositions of Acid-cleaned Single Mainstream Silicon Carbides from Murchison

We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated 88Sr/86Sr and 138Ba/136Ba ratios in mainstream SiC grains, we are able to resolve the effect of 13C concentration from that of 13C-pocket mass on s-process nucleosynthesis, which points toward the existence of large 13C pockets with low 13C concentrations in asymptotic giant branch stars. The presence of such large 13C pockets with a variety of relatively low 13C concentrations seems to require multiple mixing processes in parent asymptotic giant branch stars of mainstream SiC grain

Probing host pathogen cross-talk by transcriptional profiling of both Mycobacterium tuberculosis and infected human dendritic cells and macrophages

This study provides the proof of principle that probing the host and the microbe transcriptomes simultaneously is a valuable means to accessing unique information on host pathogen interactions. Our results also underline the extraordinary plasticity of host cell and pathogen responses to infection, and provide a solid framework to further understand the complex mechanisms involved in immunity to M. tuberculosis and in mycobacterial adaptation to different intracellular environments

Parasite fate and involvement of infected cells in the induction of CD4+ and CD8+ T cell responses to Toxoplasma gondii

During infection with the intracellular parasite Toxoplasma gondii, the presentation of parasite-derived antigens to CD4+ and CD8+ T cells is essential for long-term resistance to this pathogen. Fundamental questions remain regarding the roles of phagocytosis and active invasion in the events that lead to the processing and presentation of parasite antigens. To understand the most proximal events in this process, an attenuated non-replicating strain of T. gondii (the cpsII strain) was combined with a cytometry-based approach to distinguish active invasion from phagocytic uptake. In vivo studies revealed that T. gondii disproportionately infected dendritic cells and macrophages, and that infected dendritic cells and macrophages displayed an activated phenotype characterized by enhanced levels of CD86 compared to cells that had phagocytosed the parasite, thus suggesting a role for these cells in priming naïve T cells. Indeed, dendritic cells were required for optimal CD4+ and CD8+ T cell responses, and the phagocytosis of heat-killed or invasion-blocked parasites was not sufficient to induce T cell responses. Rather, the selective transfer of cpsII-infected dendritic cells or macrophages (but not those that had phagocytosed the parasite) to naïve mice potently induced CD4+ and CD8+ T cell responses, and conferred protection against challenge with virulent T. gondii. Collectively, these results point toward a critical role for actively infected host cells in initiating T. gondii-specific CD4+ and CD8+ T cell responses

Search for Pair Production of Third-Generation Leptoquarks and Top Squarks in pp Collisions at √s=7 TeV

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a τ lepton and a b quark. The search is based on a data sample of pp collisions at √s=7  TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8  fb[superscript -1]. The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a τ lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, τ lepton, and b quark, λ333′ are obtained. These results are the most stringent for these scenarios to date