Argentina is faced with the challenging problem ofdeveloping technology for near-surface disposal and isolation of low- andintermediate-level radioactive waste (LILW). The preferred option fordisposal of LILW (including both relatively short-lived and long-livedradionuclides) is to use disposal facilities that arenear-surface--either above or below ground level [IAEA, 1985; 2001a;2004]. How individual components of a waste disposal system perform(including waste forms, waste containers, engineered barriers and hostenvironment) will determine system safety and the safety of thesurrounding environment [IAEA, 1999]. The lack of appropriate engineeringfor the backfill, and for the selection of sealing and covering materialsfor trenches, vaults, and ditches, could result in the escape ofradionuclides from the disposed wastes [IAEA, 1994a; 2001b]. Therefore,assessment and design of backfill, barriers, and cover materials are veryimportant, both for preventing invasion of water into the disposalsystem, and for retarding radionuclides that could potentially migratefrom the system into the atmosphere or groundwater [IAEA, 1982; 1994b;2001a].

The synthesis and characterization of 1-10 nm Si nanocrystals highly resistant to oxidation is described. The nanocrystals were prepared by thermal decomposition of tetramethylsilane at 680 C, or in a gold- induced catalytic process at lower temperatures down to 400-450 C using trioctylamine as an initial solvent. Transmission electron microscopic analysis of samples obtained in the presence of gold show that the nanocrystals form via solid-phase epitaxial attachment of Si to the gold crystal lattice. The results of computational modeling performed using first principles density functional theory (DFT) calculations predict that the enhanced stability of nanocrystals to oxidation is due to the presence of N or N-containing groups on the surface of nanocrystals.

Article on hexagon versus trimer formation in In nanowires on Si(111).

The electromagnetic particle-in-cell (PIC) code VORPAL is being used to simulate the interaction of microwave radiation through an electron cloud. The results so far showgood agreement with theory for simple cases. The study has been motivated by previous experimental work on this problem at the CERN SPS [1], experiments at the PEP-II Low Energy Ring (LER) at SLAC [4], and proposed experiments at the Fermilab Main Injector (MI). With experimental observation of quantities such as amplitude, phase and spectrum of the output microwave radiation and with support from simulations for different cloud densities and applied magnetic fields, this technique can prove to be a useful probe for assessing the presence as well as the densityof electron clouds.

Solid low-level radioactive wastes at the Savannah River Site (SRS) are disposed in trenches. In order to determine the permissible radioactive inventory limits for such disposal facilities, it is required to assess the behavior of radioactive waste material over long periods of time. The sensitivity of flow and I-129 (and similar radionuclides) transport in groundwater in the vadose zone to the hydraulic conductivities of the vadose zone subregions and the low-level waste is identified and quantified. A trench configuration and simulation model have been developed to analyze the flow and transport of the radionuclide in the vadose zone as it migrates to the groundwater table. The analysis identifies and quantifies the major dependencies of the flow and radionuclide fractional flux on the subregion hydraulic conductivities. Analysis results indicate the importance of the hydraulic conductivity assigned to the materials modeled, thereby providing the modeler and decision makers with valuable insights on the potential impact of the hydraulic conductivity on flow and radionuclide transport.

When a fixed anode x-ray tube is placed in a magnetic field (B) that is parallel to the anode-cathode axis, the x-ray exposure increases with increasing B. It was hypothesized that the increase was caused by backscattered electrons which were constrained by B and reaccelerated by the electric field onto the x-ray tube target. We performed computer simulations and physical experiments to study the behavior of the backscattered electrons in a magnetic field, and their effects on the radiation output, x-ray spectrum, and off-focal radiation. A Monte Carlo program (EGS4) was used to generate the combined energy and angular distribution of the backscattered electrons. The electron trajectories were traced and their landing locations back on the anode were calculated. Radiation emission from each point was modeled with published data (IPEM Report 78), and thus the exposure rate and x-ray spectrum with the contribution of backscattered electrons could be predicted. The point spread function for a pencil beam of electrons was generated and then convolved with the density map of primary electrons incident on the anode as simulated with a finite element program (Opera-3d, Vector Fields, UK). The total spatial distribution of x-ray emission could then be calculated. Simulations showed that …

Ecosystem health with its near infinite number of variables is difficult to measure, and there are many opinions as to which variables are most important, most easily measured, and most robust, Bioassessment avoids the controversy of choosing which physical and chemical parameters to measure because it uses responses of a community of organisms that integrate all aspects of the system in question. A variety of bioassessment methods have been successfully applied to aquatic ecosystems using fish and macroinvertebrate communities. Terrestrial biotic index methods are less developed than those for aquatic systems and we are seeking to address this problem here. This study had as its objective to examine the baseline differences in ant communities at different seral stages from clear cut back to mature pine plantation as a precursor to developing a bioassessment protocol. Comparative sampling was conducted at four seral stages; clearcut, 5 year, 15 year and mature pine plantation stands. Soil and vegetation data were collected at each site. All ants collected were preserved in 70% ethyl alcohol and identified to genus. Analysis of the ant data indicates that ants respond strongly to the habitat changes that accompany ecological succession in managed pine forests and that individual genera …

Simulation of ductile fracture at the atomic scale reveals many aspects of the fracture process including specific mechanisms associated with void nucleation and growth as a precursor to fracture and the plastic deformation of the material surrounding the voids and cracks. Recently we have studied void coalescence in ductile metals using large-scale atomistic and continuum simulations. Here we review that work and present some related investigations. The atomistic simulations involve three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. No pronounced shear flow is found in the coalescence process. We also discuss a technique for optimizing the calculation of fine-scale information …

We report the discovery of a self-doped multilayer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi-surface sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60 K, possessing simultaneously both electron- and hole-doped Fermi-surface sheets. Intriguingly, the Fermi-surface sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/{alpha}, {pi}/{alpha}) scattering.

We discuss images of the central {approx} 10 kpc (in projection) of the galaxy merger NGC 6240 at H and K{prime} bands, taken with the NIRC2 narrow camera on Keck II using natural guide star adaptive optics. We detect 28 star clusters in the NIRC2 images, of which only 7 can be seen in the similar-spatial-resolution, archival WFPC2 Planetary Camera data at either B or I bands. Combining the NIRC2 narrow camera pointings with wider NICMOS NIC2 images taken with the F110W, F160W, and F222M filters, we identify a total of 32 clusters that are detected in at least one of these 5 infrared ({lambda}{sub c} > 1 {micro}m) bandpasses. By comparing to instantaneous burst, stellar population synthesis models (Bruzual & Charlot 2003), we estimate that most of the clusters are consistent with being {approx} 15 Myr old and have photometric masses ranging from 7 x 10{sup 5} M{sub {circle_dot}} to 4 x 10{sup 7}M{sub {circle_dot}}. The total contribution to the star formation rate (SFR) from these clusters is approximately 10M{sub {circle_dot}} yr{sup -1}, or {approx} 10% of the total SFR in the nuclear region. We use these newly discovered clusters to estimate the extinction toward NGC 6240's double nuclei, …

Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60 MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12 MeV.

The Department of Energy Office of Environmental Management (DOE/EM) plans to conduct the Plutonium Disposition Project at the Savannah River Site (SRS) in Aiken, SC, to disposition excess weapons-usable plutonium. A plutonium glass waste form is a leading candidate for immobilization of the plutonium for subsequent disposition in a geologic repository. The objectives of this present task were to fabricate plutonium-loaded lanthanide borosilicate (LaBS) Frit B glass and perform testing to provide near-term data that will increase confidence that LaBS glass product is suitable for disposal in the proposed Federal Repository. Specifically, testing was conducted in an effort to provide data to Yucca Mountain Project (YMP) personnel for use in performance assessment calculations. Plutonium containing LaBS glass with the Frit B composition with a 9.5 wt% PuO{sub 2} loading was prepared for testing. Glass was prepared to support glass durability testing via the ASTM Product Consistency Testing (PCT) at Savannah River National Laboratory (SRNL). The glass was characterized with X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) prior to performance testing. This characterization revealed some crystalline PuO{sub 2} inclusions with disk-like morphology present in the as fabricated, quench-cooled glass. A series of PCTs was conducted …

Experiments at the FLASH facility at DESY have demonstrated that the higher order modes induced in superconducting cavities can be used to provide a variety of beam and cavity diagnostics. The axes of the modes can be determined from the beam orbit that produces minimum power in the dipole HOM modes. The phase and amplitude of the dipole modes can be used to obtain high resolution beam position information, and the phase of the monopole modes to measure the beam phase relative to the accelerator rf. For most superconducting accelerators, the existing higher order mode couplers provide the necessary signals, and the downmix and digitizing electronics are straightforward, similar to those for a conventional beam position monitor.

A new laser-wire (LW) system has been installed at the ATF extraction line at KEK, Tsukuba. The system aims at a micron-scale laser spot size and employs a mode-locked laser system. The purpose-built interaction chamber, light delivery optics, and lens systems are described, and the first results are presented.

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We report the first experimental observation of sequential, multiple polymorphic phase transformations occurring in Praseodymium dynamically compressed using a ramp wave. The experiments also display the signatures of reverse transformations occuring upon pressure release and reveal the presence of small hysteresys loops. The results are in very good agreement with equilibrium hydrodynamic calculations performed using a thermodynamically consistent, multi-phase equation of state for Praseodymium, suggesting a near-equilibrium transformation behavior.

The cosmic microwave background power spectra are studied for different families of single field new and chaotic inflation models in the effective field theory approach to inflation. We implement a systematic expansion in 1/N(e), where N(e)~;;50 is the number of e-folds before the end of inflation. We study the dependence of the observables (n(s), r and dn(s)/dlnk) on the degree of the potential (2n) and confront them to the WMAP3 and large scale structure data: This shows in general that fourth degree potentials (n=2) provide the best fit to the data; the window of consistency with the WMAP3 and LSS data narrows for growing n. New inflation yields a good fit to the r and n(s) data in a wide range of field and parameter space. Small field inflation yields r<0.16 while large field inflation yields r>0.16 (for N(e)=50). All members of the new inflation family predict a small but negative running -4(n+1) x 10-4<=dn(s)/dlnk<=-2 x 10-4. (The values of r, n(s), dn(s)/dlnk for arbitrary N(e) follow by a simple rescaling from the N(e)=50 values.) A reconstruction program is carried out suggesting quite generally that for n(s) consistent with the WMAP3 and LSS data and r<0.1 the symmetry breaking scale …

We perform an analysis of the production of elements with mass number A {ge} 12 in a standard Big Bang Nucleosynthesis scenario. The goal is to provide a more accurate estimate of the very low and yet poorly explored abundance of such elements, relevant for the pristine Population III stars. We examine the synthesis channels for these elements in a critically revised and updated version of the Wagoner-Kawano code, as well as in a further enlarged version including four additional nuclides and a significantly extended nuclear network. Our results show no major discrepancies with the ones obtained using a smaller nuclear network. The robustness of the standard predictions--the early generation of star developed in a metal-free environment--is confirmed.

BaBar has measured with unprecedented accuracy e{sup +}e{sup -} {yields} p{bar p} from the threshold up to Q{sub p{bar p}}{sup 2} {approx} 20 GeV{sup 2}/c{sup 4}, finding out an unexpected cross section, with plateaux and drops. In particular it is well established a sharp drop near threshold, where evidence for structures in multihadronic channels has also been found. Other unexpected and spectacular features of the Nucleon form factors are reminded, the behavior of space-like G{sub E}{sup p}/G{sub M}{sup p} and the neutron time-like form factors.

In 2003, the Stanford Synchrotron Radiation Laboratory (SSRL) has upgraded its storage ring to a 3rd generation storage ring (SPEAR3). SPEAR3 is deigned to operate at 500 mA stored beam current and 3 GeV energy. The 234-meter circumference SPEAR3 ring utilizes 60-cm-thick concrete lateral walls, 30-cm-thick concrete roof, as well as 60-cm or 90-cm-thick concrete ratchet walls. A total of 3.5 x 10{sup 15} e{sup -}/y will be injected into the ring with an injection power of 4 W and an injection efficiency of 75%. Normal beam losses occur due to both injection and stored beam operations in the total of 20 low loss as well as 3 high loss limiting apertures. During the 6-minutes injection period, an instantaneous power loss of 0.05 W occurs at each low loss aperture. When averaged over the operational year, the loss of both the injection and stored beams is equivalent to an average loss of 2 mW at each low loss aperture. On the other hand, the average losses in the high loss apertures are 16 mW for the injection septum, 47 mW for the beam abort dump, and 13 mW for the ring stoppers. The shielding requirements for losses in the new …

The Geant4 hadronic models cover the entire range of energies required by calorimeters in new and planned experiments. The extension and improvement of the elastic, cascade, parameterized and quark-gluon string models will be discussed. Such improvements include the extension to more particle types, a review and correction of cross sections, and a better treatment of energy and momentum conservation. Concurrent with this development has been a validation program which includes comparisons with double differential cross sections. An ongoing hadronic shower validation will also be discussed which includes the examination of longitudinal shower shapes and the performance of the above models as well as their interaction with electromagnetic processes such as multiple scattering.

Dose control and measurement plans for the SPEAR3 Booster and storage ring have taken place during the SPEAR3 commissioning. The initial commissioning period (SPEAR3 start-up) covered the time period from the beginning of November 2003 to the early part of March 2004. The period from the beginning of March to the beginning of August 2004 has been mostly dedicated to the scientific program. The initial commissioning period was characterized with frequent injection and significantly higher losses. In comparison, the scientific program period was characterized with more stable beam operation with limited number of injections per day and lower beam losses. Three types of dose measurements, passive, active and special measurements, were implemented around the SPEAR3 Booster and storage ring. Based on the expected radiation hazards, several dose control measures were adopted at several stages of the commissioning. In the early stages of commissioning, areas within 4.5 m from the walls of the Booster and storage ring were designated as Radiation Areas (RA). Areas outside RA were classified as Radiologically Controlled Area (RCA). Access to these areas required less training than the radiation areas. A monthly review of the accelerator operation conditions and radiation measurement results were used to determine the …

TeV-scale extra dimensions may play an important role in electroweak or supersymmetry breaking. We examine the phenomenology of such dimensions, compactified on a sphere S{sup n}, n {ge} 2, and show that they possess distinct features and signatures. For example, unlike flat toroidal manifolds, spheres do not trivially allow fermion massless modes. Acceptable phenomenology then generically leads to ''non-universal'' extra dimensions with ''pole-localized'' 4-d fermions; the bosonic fields can be in the bulk. Due to spherical symmetry, some Kaluza-Klein (KK) modes of bulk gauge fields are either stable or extremely long-lived, depending on the graviton KK spectrum. Using precision electroweak data, we constrain the lightest gauge field KK modes to lie above {approx_equal} 4 TeV. We show that some of these KK resonances are within the reach of the LHC in several different production channels. The models we study can be uniquely identified by their collider signatures.

Advanced laser systems will be essential for a range of diagnostics devices and polarimetry at the ILC. High average power, high beam quality, excellent stability and reliability will be crucial in order to deliver the information required to attain the necessary ILC luminosity as well as for efficient polarimetry. The key parameters are listed together with the R & D required to achieve the necessary laser system performance.