X-ray lasers have been extensively studied around the world since the first laboratory demonstration on the Novette laser at LLNL in 1984. The characteristic properties of short wavelength, high monochromaticity, collimation and coherence make x-ray lasers useful for various applications. These include demonstrations of biological imaging within the water window, interferometry of laser plasmas and radiography of laser-heated surfaces. One of the critical issues has been the high power pump required to produce the inversion. The power scaling as a function of x-ray laser wavelength follows a {approx} {lambda}{sup -4} to {approx} {lambda}{sup -6} law. The shortest x-ray laser wavelength of {approx}35 {angstrom} demonstrated for Ni-like Au was at the limit of Nova laser capabilities. By requiring large, high power lasers such as Nova, the shot rate and total number of shots available have limited the rapid development of x-ray lasers and applications. In fact over the last fifteen years the main thrust has been to develop more efficient, higher repetition rate x-ray lasers that can be readily scaled to shorter wavelengths. The recent state of progress in the field can be found in references. The objective of the project was to develop a soft x-ray laser (XRL) pumped by …

We built a bi-directional scatter diagnostics to measure and quantify losses due to scattering and absorption of harmonic conversion crystals (DKDP) for the National Ignition Facility (NIF). The main issues to be addressed are (1) amount of total energy reaching the target if the target hole was {+-}200 {micro}rad in size, (2) distribution of energy inside the target hole, (3) collateral damage of other optics by scattered light. The scatter diagnostics enables angle-resolved measurements at 351 nm, and is capable of both near specular transmission and large angle scatter measurements. In the near specular setup, the transmission can be measured within {+-}65 {micro}rad up to {+-}60 mrad acceptance angle. A silicon photo detector and a scientific-grade CCD camera provide total energy and energy distribution. A linear swing arm detection system enables large angle scatter measurements of 360{sup o}, in principal, with step sizes as small as 0.01{sup o} and different collection angle ranging between 1 and 20 mad. In this paper, scatter effects from laser damage and final finishing process of DKDP are discussed.

The ENDF/B data library has recently been updated and is now freely available through the National Nuclear Data Center (NNDC), Brookhaven National Laboratory. This most recent library is identified as ENDF/B-VI, Release 7. Release 7 completely supersedes all preceding releases. As distributed the ENDF/B-VI, Release 7 data includes cross sections represented in the form of a combination of resonance parameters and/or tabulated energy dependent cross sections, nominally at 0 Kelvin temperature. For use in applications this library has been processed into the form of temperature dependent cross sections at eight temperatures between 0 and 2100 Kelvin, in steps of 300 Kelvin. At each temperature the cross sections are tabulated and linearly interpolable in energy. All results are in the computer independent ENDF/B-VI character format [1], which allows the data to be easily transported between computers. In its processed form this library is approximately 1.6 gigabyte in size and is distributed on three CDs.

This section reviews extensions and variations of the direct-semidirect (DSD) model for understanding the high-energy component of gamma spectra resulting from radiative capture of fast nucleons; i.e., the part of the spectrum that is not amenable to standard statistical model (Hauser-Feshbach) treatments. We describe recent results on the extension of the DSD model to unbound final states, including comparison with proton and neutron capture data. The importance of including convective-current magnetic radiation to explain proton capture angular distributions in the 30 MeV region is shown. We conclude with a brief discussion of a model closely related to the DSD, the pure-resonance model.

Initial dislocation structure in annealed high-purity Mo single crystals and deformation substructure in a crystal subjected to 1% compression have been examined and studied in order to investigate dislocation multiplication mechanisms in the early stages of plastic deformation. The initial dislocation density is in a range of 10{sup 6} {approx} 10{sup 7} cm{sup -2}, and the dislocation structure is found to contain many grown-in superjogs along dislocation lines. The dislocation density increases to a range of 10{sup 8} {approx} 10{sup 9} cm{sup -2}, and the average jog height is also found to increase after compressing for a total strain of 1%. It is proposed that the preexisting jogged screw dislocations can act as (multiple) dislocation multiplication sources when deformed under quasi-static conditions. Both the jog height and length of link segment (between jogs) can increase by stress-induced jog coalescence, which takes place via the lateral migration (drift) of superjogs driven by unbalanced line-tension partials acting on link segments of unequal lengths. Applied shear stress begins to push each link segment to precede dislocation multiplication when link length and jog height are greater than critical lengths. This dynamic dislocation multiplication source is subsequently verified by direct simulations of dislocation dynamics under …

Algebraic multigrid (AMG) is an attractive choice for solving large linear systems {Lambda}x = b on unstructured grids. While AMG is applicable as a solver for a variety of problems, its robustness may be enhanced by using it as a preconditioner for Krylov solvers, such as GMRES. The sheer size of modern problems, hundreds of millions or billions of unknowns, dictates the use of massively parallel computers. AMG consists of two phases: the setup phase, in which smaller and smaller linear systems are generated by means of linear transfer operators (interpolation and restriction); and the solve phase, which employs a smoothing operator, such as Gauss-Seidel or Jacobi relaxation. Most of these components can be parallelized in a straightforward fashion; however, the coarse-grid selection, in which the grid for a smaller linear system is created on which the error can be approximated, is highly sequential. It is important to develop parallel coarsening techniques. They briefly present here the coarsening algorithms used in the parallel AMG code ''Boomer AMG'' and summarize some performance results for those algorithms. A detailed discussion of the algorithms and numerical results will be found.

In this section we review the available data on gamma spectra following radiative capture of neutrons above 10 MeV. A few measurements below that energy are included. An important source for references to this topic is the CINDA compilation maintained by the IAEA in cooperation with three other major data centers. An additional useful source is the review article by Weller and Roberson, which treats capture reactions with neutrons, protons, and alpha particles. The following discussion refers only to data that are easily accessible through readily-available journals, reports, or the EXFOR database. Most of the reported measurements were made for the purpose of determining cross sections for discrete states at the high energy end of the gamma spectra which are resolvable or nearly so. In only a few cases have cross sections been measured over a wide range of gamma energies. These measurements are first reviewed below, followed by a review of more detailed measurements such as angular distributions and analyzing powers. Neutron capture on hydrogen isotopes have not been included with the exception of a fairly recent measurement on deuterium; see CINDA for references to this specialized topic.

Vertical cavity surface-emitting lasers (VCSELs) are becoming increasingly important for short-haul optical fiber transmission systems. Given the commercial success of GaAs-based 850nm VCSELs, dramatic enhancements in transmission bandwidth and distance can be achieved in conventional single- and multi-mode fiber by extending the emission wavelength to the 1300nm-1550nm range. GaInNAs is a promising active layer material grown on GaAs that can achieve 1300nm emission [l], and electrically pulsed broad-area GaInNAs VCSELs [2,3] have been realized. Here we take advantage of the properties of GaAs-based materials-thermally-conductive high contrast mirrors and AlAs-oxide current apertures-to demonstrate for the first time low-threshold ({approx}1 mA) GaInNAs VCSELs emitting at a wavelength of 1200 nm under continuous-wave room temperature operation. The device structure is shown schematically in figure 1. The bottom mirror consists of a 22.5-period n-doped GaAs/AlAs distributed Bragg reflector (DBR) designed for a center wavelength {lambda} near 1200nm, the top mirror is a 22-period p-doped DBR whose reflectance is enhanced by a Ti/Au contact electrode, and the GaAs {lambda} cavity contains three 70{angstrom}, Ga{sub 0.3}In{sub 0.7}N{sub 0.02}As{sub 0.98} quantum wells (QWs) separated by 200{angstrom} GaAs barriers. The epilayers were grown by molecular beam epitaxy using solid-source arsenic and a rf nitrogen plasma source. After growth, …

The problem of silica scale formation is common in geothermal power production facilities worldwide. Factors such as variable fluid compositions, different plant operating conditions, and the complex nature of silica polymerization reactions contribute to make scale inhibition a difficult problem. Scale forms by molecular and particle (colloid) deposition. Colloids are produced by polymerization of aqueous silica. One approach to controlling silica scale is to use water-soluble organic polymers that inhibit or delay the onset of polymerization. Laboratory batch experiments are being performed to test the ability of commercially available antiscalants to extend the length of the induction period during silica polymerization. The induction period should be long enough to allow the brine to pass through the surface and reinjection facilities before colloid deposition occurs. Potential antiscalants will then be tested under field conditions at a geothermal power plant.

Decision trees have long been popular in classification as they use simple and easy-to-understand tests at each node. Most variants of decision trees test a single attribute at a node, leading to axis-parallel trees, where the test results in a hyperplane which is parallel to one of the dimensions in the attribute space. These trees can be rather large and inaccurate in cases where the concept to be learnt is best approximated by oblique hyperplanes. In such cases, it may be more appropriate to use an oblique decision tree, where the decision at each node is a linear combination of the attributes. Oblique decision trees have not gained wide popularity in part due to the complexity of constructing good oblique splits and the tendency of existing splitting algorithms to get stuck in local minima. Several alternatives have been proposed to handle these problems including randomization in conjunction with deterministic hill climbing and the use of simulated annealing. In this paper, they use evolutionary algorithms (EAs) to determine the split. EAs are well suited for this problem because of their global search properties, their tolerance to noisy fitness evaluations, and their scalability to large dimensional search spaces. They demonstrate the technique …

We investigated chemical etching as a possible means to mitigate the growth of UV laser-induced surface damage on fused silica. The intent of this work is to examine the growth behavior of existing damage sites that have been processed to remove the UV absorbing, thermo-chemically modified material within the affected area. The study involved chemical etching of laser-induced surface damage sites on fused silica substrates, characterizing the etched sites using scanning electron microscopy (SEM) and laser fluorescence, and testing the growth behavior of the etched sites upon illumination with multiple pulses of 351nm laser light. The results show that damage sites that have been etched to depths greater than about 9 {micro}m have about a 40% chance for zero growth with 1000 shots at fluences of 6.8-9.4 J/cm{sup 2}. For the etched sites that grow, the growth rates are consistent with those for non-etched sites. There is a weak dependence of the total fluorescence emission with the etch depth of a site, but the total fluorescence intensity from an etched site is not well correlated with the propensity of the site to grow. Deep wet etching shows some promise for mitigating damage growth in fused silica, but fluorescence does not …

The U.S. Department of Energy, Office of Fusion Energy Science (OFES) formed the Virtual Laboratory for Technology (VLT) to develop the technologies needed to support near term fusion experiments and to provide the basis for future magnetic and inertial fusion energy power plants. The scope of the inertial fusion energy (IFE) element of the VLT includes the fusion chamber, driver/chamber interface, target fabrication and injection, and safety and environmental assessment for IFE. Lawrence Livermore National Laboratory, in conjunction with other laboratories, universities and industry, has written an R&D plan to address the critical issues in these areas over the next 5 years in a coordinated manner. This paper provides an overview of the US. research activities addressing these critical issues.

Lightweight hydrogen storage for vehicles is enabled by adopting and adapting aerospace tankage technology. The weight, volume, and cost are already acceptable and improving. Prototype tankage was demonstrated with 11.3% hydrogen by weight, 1.74 million inch (44.3 km) burst performance factor (P{sub b}V/W), and 3.77 kWh/kg specific energy for the tank and hydrogen (LHV). DOE cannot afford full scale aerospace development costs. For example, it costs many tens of $M to develop a rocket motor casing with a safety factor (SF) of 1.25. Large teams of experts are required to design, develop, and test new processes. Car companies are buying existing technology with only modest investments in research and development (R&D). The Lawrence Livermore National Laboratory (LLNL) team is maximizing the leverage from DOE funding by joining with industry to solve technical risks at the component level. LLNL is developing fabrication processes with IMPCO Technologies, Thiokol Propulsion, and Aero Tec Laboratories (ATL). LLNL is creating commercial products that are close to adoption under DOE solicitation. LLNL is breaking ground to achieve greater than 10% hydrogen by weight tankage with safety that exceeds the requirements of NGV2 standards modified for hydrogen. Risk reduction is proceeding along three axes: (1) Commercializable products …

Advanced in technology have enabled us to collect data from observations, experiments, and simulations at an ever increasing pace. As these data sets approach the terabyte and petabyte range, scientists are increasingly using semi-automated techniques from data mining and pattern recognition to find useful information in the data. In order for data mining to be successful, the raw data must first be processed into a form suitable for the detection of patterns. When the data is in the form of images, this can involve a substantial amount of processing on very large data sets. To help make this task more efficient, they are designing and implementing an object-oriented image processing toolkit that specifically targets massively-parallel, distributed-memory architectures. They first show that it is possible to use object-oriented technology to effectively address the diverse needs of image applications. Next, they describe how we abstract out the similarities in image processing algorithms to enable re-use in the software. They will also discuss the difficulties encountered in parallelizing image algorithms on massively parallel machines as well as the bottlenecks to high performance. They will demonstrate the work using images from an astronomical data set, and illustrate how techniques such as filters and denoising …

The National Ignition Facility will require hundreds of very large single crystals (boules) of KDP and KD*P for the amplifier and frequency conversion optics. Rapid growth now routinely produces 250-300 kg boules of KDP. Technical hurdles overcome during the past year include inclusion formation and spurious nucleation. Areas of continued interest are control of asymmetry and aspect ratio. Variations in KDP concentration on the pm scale at the growing crystal steps can cause inclusions of growth solution. Microscopic investigations, hydrodynamic modeling, and theoretical modeling have been combined to provide a good mechanistic understanding of the formation of inclusions. Modifications to rotation regimes to improve hydrodynamics can eliminate or minimize the effects of these instability mechanisms, and can increase the inclusion-free growth rate by 20-40% over previously observed growth rates. Aspect ratio and boule asymmetry remains of great interest. Small changes in asymmetry can result in significant increases in maximum yields for boules of the same mass. Reasons for the observed changes in aspect ratio during growth will be presented, along with methods to control or influence aspect ratio and boule asymmetry.

A thick flowing layer of liquid (e.g., flibe--a molten salt, or Sn{sub 80}Li{sub 20}--a liquid metal) protects the structural walls of the field-reversed configuration (FRC) so that they can last the life of the plant even with intense 14 MeV neutron bombardment from the D-T fusion reaction. The surface temperature of the liquid rises as it passes from the inlet nozzles to the exit or receiver nozzles due to absorption of line and bremsstrahlung radiation, and neutrons. The surface temperature can be reduced by enhancement of convection near the surface to transport hot surface liquid into the cooler interior. This surface temperature must be compatible with a practical heat transport and energy recovery system. The evaporative flux from the wall driven by the surface temperature must also result in an acceptable impurity level in the core plasma. The shielding of the core by the edge plasma is modeled with a 2D transport code for the resulting impurity ions; these ions are either swept out to the distant end tanks, or diffuse to the hot plasma core. An auxiliary plasma between the edge plasma and the liquid wall can further attenuate evaporating flux of atoms and molecules by ionization. The current …

This report documents the C version of the MCAPM (Monte Carlo All Particle Method) generator and collision physics library of subroutines. The Monte Carlo data generator (gen2000) reads cross sections and distributions that describe in-flight reactions from a binary library and creates an internal data library. The collision routines (bang2000) use this internal library to perform the physics of interaction of particles with the background material. Particles modeled with MCAPM-C are neutrons, charged particles (p, d, t, {sup 3}He, and {alpha}), and {gamma}'s. MCAPM-C is written in (nearly) standard C, and versions exist for Sun Solaris, Compaq Unix, IBM AIX, SGI Irix, and Linux. The library and its data files are installed on LC's Compass, TC, Forest, Blue, and Sky machines. This report describes the contents and format of the library, physics assumptions made, and the interface to the library's subroutines.

The experimental validation of first principals calculations of plutonium and its alloys is an important part of LLNL's science-based stockpile stewardship mission. This project has addressed this issue in the following ways. We have measured the electronic structure of U, Pu, and their alloys using valence band photoemission (PES), Soft X-Ray fluorescence (SXF), and X-Ray Absorption Spectroscopy (XAS). In the long term, this will allow a direct comparison between calculated and measured density of electronic states, identifying the degree of f-electron localization in the alloys, and thus, permit selection of the best modeling code.

Newsletter of the Texas Department of Health discussing the news, activities, and events of the organization and other information related to health in Texas.

The subject of tritium production in the Antiproton Source Collection lens was raised in the mid-1980s during the design phase of the pbar source. Interest in it has recurred during development of the proton lens and in recent investigations to determine the feasibility of liquid lithium collection lenses for the pbar source and a muon collider project. Calculations for tritium and beryllium 7 production on lithium suffer from a lack of information on medium and high energy cross section data. In addition, knowledge of the energy spectrum within the target vault is based upon calculations. Knowledge of the low energy spectrum, important for tritium production on lithium, is limited, if not non-existent. For Collider Run II, effort is to be applied to improve the performance of the solid lithium lens. Historically, examination of failed lithium lenses has not been pursued because they have been fairly radioactive and because they are thought to contain significant quantities of the radionuclides tritium and beryllium 7. The development of methods to examine failed lithium lenses may be desirable so that the specific causes of failure can be discovered. From such studies, design improvements can be incorporated with the goal of achieving lens performances goals …

This document discusses the sampling of strontium-90 on the Hanford Site and any implications it may have to the ecology of the area.

This brief paper concludes our study of the origin of the 871-keV observed for many plutonium oxide samples.

The purpose of this calculation is to determine the effects on long-term dose from disposing of selected U. S. Department of Energy (DOE) spent nuclear fuel (DSNF) in high integrity cans (HICs). The Civilian Radioactive Waste Management System Management and Operating contractor (CRWMS M&O) prepared the calculation as part of Performance Assessment (PA) activities for the DOE Yucca Mountain Project. DSNF encompasses approximately 2,500 MTHM (metric tons heavy metal) consisting of over 200 fuel types that have been categorized into 11 groups, referred to as Groups 1 to 11, to facilitate their performance assessment (DOE 1999a, Sec. 5). DSNF and high level waste (HLW) have been allocated 7,000 MTHM or 10% of the 70,000 MTHM of nuclear waste scheduled for disposal at Yucca Mountain (DOE 1999a, Sec. 8.1). Of the 7,000 MTHM, 2,333 will be DSNF, or 93% of all 2,500 MTHM of DSNF, and 4,667 MTHM equivalent will be HLW (DOE 1999a, Sec. 8.1). The DOE spent fuels selected for HIC disposal are those that are poorly characterized, fragmented, or damaged, and the HIC concept is intended to provide additional protection by delaying the radionuclide release to ensure that environmental and/or regulatory standards are met.

This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.