We identify the binding sites for adsorption of a single Ge atom on the Si(100) surface using ab initio total energy calculations. The calculated diffusion barriers are in excellent agreement with experimental estimates. Using a large supercell we resolve the controversy regarding the binding geometry and migration path for the adatom, and investigate the influence of the adatom on the buckling of Si dimers. The adatom induces a buckling defect that is frequently observed using scanning tunneling microscopy (STM); therefore the study of single adatoms may be experimentally accessible.

The Advanced Photon Source (APS) vacuum system has been designed to be passively safe from bending magnet radiation heating at positron beam currents up to 30 mA. Above this value, certain components may be damaged from vertical beam missteering, although work is proceeding to raise the safe current threshold. Because of this, a system for preventing the misalignment of high power density beams is required. This report details a system for protection from dipole radiation only. Work on a system for ID radiation is continuing.

The Advanced Photon Source (APS) vacuum system has been designed to be passively safe from bending magnet radiation heating at positron beam currents up to 30 mA. Above this value, certain components may be damaged from vertical beam missteering, although work is proceeding to raise the safe current threshold. Because of this, a system for preventing the misalignment of high power density beams is required. This report details a system for protection from dipole radiation only. Work on a system for ID radiation is continuing.

The interaction of subpicosecond 1.06 mm laser light at intensities up to 10{sup 18} W/cm{sup 2} with dense performed plasmas is investigated by measurements of the absorption of the laser light in the plasma and by measurements of the production of bremsstrahlung x-rays. Absorption measurements are made by collecting the scattered light in an Ulbricht sphere. Light scattered in the backward and specular directions is collected separately. Measurements are presented for both high and low Z targets. X-ray production is measured using a nine channel filter/scintillator spectrometer.

This volume contains the abstracts of oral and poster presentations made at the LVIII Cold Spring Harbor Symposium on Quantitative Biology entitles DNA & Chromosomes. The meeting was held June 2--June 9, 1993 at Cold Spring Harbor, New York.

Less than 100 abstracts are included.

Objective of the Advanced Research and Technology Development materials program is to conduct R and D on materials for fossil energy applications (coal processing, coal liquefaction, gasification, heat engines and recovery, combustion systems, fuel cells). Research is aimed at better understanding of materials in fossil energy environments and development of new materials for improvement of plant operations and reliability. Abstracts are given of 37 papers on ceramics/composites, intermetallics (iron aluminides, etc.), and advanced austenitics. (DLC)

This report provides a status of the expedited response action (ERA) projects currently being implemented at the Hanford Site. A detailed review of the accomplishments to date, the technologies employed, the problems encountered, and an analysis of the lessons learned are included. A total of nine ERAs have been initiated at the Hanford Site and are presented in a case study format with emphasis on the progress being made and the challenges ahead.

Cementitious materials may be employed in settings where they face prolonged exposure to Mg-rich brines. This study evaluated the possibility of using high temperatures to accelerate brine-cement reaction rates. Class-H cement coupons were tested in Mg-K-Na-C1- SO{sub 4} brines to 100{degrees}C. MgC1{sub 2}-NaC1 solutions were also employed in a test sequence that extended to 200{degrees}C. It was found that accelerated testing could be used successfully to evaluate the compatability of cementitious materials with such brines.

The origin of cosmic rays and applicable laboratory experiments are discussed. Some of the problems of shock acceleration for the production of cosmic rays are discussed in the context of astrophysical conditions. These are: The presumed unique explanation of the power law spectrum is shown instead to be a universal property of all lossy accelerators; the extraordinary isotropy of cosmic rays and the limited diffusion distances implied by supernova induced shock acceleration requires a more frequent and space-filling source than supernovae; the near perfect adiabaticity of strong hydromagnetic turbulence necessary for reflecting the accelerated particles each doubling in energy roughly 10{sup 5} to {sup 6} scatterings with negligible energy loss seems most unlikely; the evidence for acceleration due to quasi-parallel heliosphere shocks is weak. There is small evidence for the expected strong hydromagnetic turbulence, and instead, only a small number of particles accelerate after only a few shock traversals; the acceleration of electrons in the same collisionless shock that accelerates ions is difficult to reconcile with the theoretical picture of strong hydromagnetic turbulence that reflects the ions. The hydromagnetic turbulence will appear adiabatic to the electrons at their much higher Larmor frequency and so the electrons should not be scattered …

During the Remedial Investigation and Feasibility Study (RI/FS) phase of a CERCLA cleanup, it is possible to implement interim actions at a site ``to respond to an immediate site threat or take advantage of an opportunity to significantly reduce risk quickly.`` An interim action is a short term action that addresses threats to public health and safety and is generally followed by the RI/FS process to achieve complete long term protection of human health and the environment. Typically, an interim action is small in scope and can be implemented quickly to reduce risks, such as the addition of a security fence around a known or suspected hazard, or construction of a temporary cap to reduce run-on/run-off from a contaminant source. For more specialized situations, however, the possibility exists to apply the intent of the interim action guidance to a much larger project scope. The primary focus of this paper is the discussion of the interim action approach for streamlined remedial action and presentation of an example large-scale project utilizing this approach at the Fernald Environmental Management Project (FEMP).

This report contains viewgraphs on accelerator design and physics.

This report contains viewgraphs on accelerator design and physics.

An experimental station for an X-band Next Linear Collider has been constructed at SLAC. This station consists of a klystron and modulator, a low-loss waveguide system for rf power distribution, a SLED II pulse-compression and peak-power multiplication system, acceleration sections and beam-line components (gun, prebuncher, preaccelerator, focussing elements and spectrometer). An extensive program of experiments to evaluate the performance of all components is underway. The station is described in detail in this paper, and results to date are presented.

An accelerator-based conversion (ABC) system is presented that is capable of rapidly burning plutonium in a low-inventory sub-critical system. The system also returns fission power to the grid and transmutes troublesome long-lived fission products to short lived or stable products. Higher actinides are totally fissioned. The system is suited not only to controlled, rapid burning of excess weapons plutonium, but to the long range application of eliminating or drastically reducing the world total inventory of plutonium. Deployment of the system will require the successful resolution of a broad range of technical issues introduced in the paper.

This paper attempts to summarize the neutrino oscillation section of the Workshop on Future Directions in Particle and Nuclear Physics at Multi-GeV Hadron Beam Facilities. There were very lively discussions about the merits of the different oscillation channels, experiments, and facilities, but we believe a substantial consensus emerged. First, the next decade is one of great potential for discovery in neutrino physics, but it is also one of great peril. The possibility that neutrino oscillations explain the solar neutrino and atmospheric neutrino experiments, and the indirect evidence that Hot Dark Matter (HDM) in the form of light neutrinos might make up 30% of the mass of the universe, point to areas where accelerator-based experiments could play a crucial role in piecing together the puzzle. At the same time, the field faces a very uncertain future. The LSND experiment at LAMPF is the only funded neutrino oscillation experiment in the United States and it is threatened by the abrupt shutdown of LAMPF proposed for fiscal 1994. The future of neutrino physics at the Brookhaven National Laboratory AGS depends the continuation of High Energy Physics (HEP) funding after the RHIC startup. Most proposed neutrino oscillation searches at Fermilab depend on the completion …

Biological effects occur in natural systems at chemical concentrations of parts per billion (1:10{sup 9}) or less. Affected biomolecules may be separable in only milligram or microgram quantities. Quantification at attomole sensitivity is needed to study these interactions. AMS measures isotope concentrations to parts per 10{sup 13--15} on milligram-sized samples and is ideal for quantifying long-lived radioisotopic labels that are commonly used to trace biochemical pathways in natural systems. {sup 14}C-AMS has now been coupled to a variety of organic separation and definition technologies. The primary research investigates pharmacokinetics and genotoxicities of toxins and drugs at very low doses. Human subject research using AMS includes nutrition, toxicity and elemental balance studies. {sup 3} H, {sup 41}Ca and {sup 26}Al are also traced by AMS for fundamental biochemical kinetic research. Expansion of biomedical AMS awaits further development of biochemical and accelerator technologies designed specifically for these applications.

Work is in progress on interactive tools for linear and nonlinear accelerator design, analysis, and simulation using X-based graphics. The BEAMLINE and MXYZPTLK class libraries, were used with an X Windows graphics library to build a program for interactively editing lattices and studying their properties.

Realization of the design energy and luminosity goals of the Superconducting Super Collider (SSC) will require proper resolutions of a number of challenging problems in accelerator physics. The status of several salient issues in the design of the SSC will be reviewed and updated in this paper. The emphasis will be on the superconducting accelerators.

In the program of work directed towards the development of an X-Band Next Linear Collider accelerator structure, two different test accelerator sections have been completed, and a third is being fabricated. The first is a simple 30-cell constant-impedance section in which no special attention was given to surface finish, pumping, and alignment. The second is an 86-cell section in which the cells were precision diamond-turned by Texas Instruments Inc. The structure has internal water-cooling and vacuum pumping manifolds. Some design details are given for the third section, which is a 206-cell structure with cavities dimensioned to give a Gaussian distribution of dipole mode frequencies. It has conventional-machining surface finishes and external water and pumping manifolds. Component design, fabrication, and assembly brazing are described for the first two experimental sections.

Researchers at Los Alamos have been developing transmutation concepts involving accelerator-driven nuclear systems. A medium energy, high current proton beam strikes a heavy metal target, producing a high flux of spallation neutrons. These neutrons are moderated to near-thermal energies in a blanket surrounding the target. Materials to be transmuted flow through the blanket region where they are fissioned or transmuted to stable nuclides. Stable or short-lived nuclides are separated while the long-lived radioactive species are returned to the blanket. For most applications the fission energy produced is much greater than that required to power the accelerator and can be directed to the commercial power grid. A number of possible applications are envisioned for accelerator-driven nuclear systems. These include destruction of surplus weapons-grade plutonium, production of tritium, transmutation of commercial spent fuel, and even commercial power generation in next-generation nuclear power plants. Some of these applications will be discussed with particular emphasis on the required chemical separations for such systems.

Versions of the CINDER code have been used over three decades for determination of reactor fuel inventories and aggregate neutron absorption and radioactive decay properties. The CINDER`90 code, an evolving version which requires no predetermined nuclide chain structure, is suitable for a wider range of transmutation problems including those treated with older versions. In recent accelerator transmutation studies, the CINDER`90 code has been linked with the LAHET Code System (LCS) and, for high-energy calculations, with SUPERHET. A description of the nature of these linked calculational tools is given; data requirements for the transmutation studies are described; and, examples of linked calculations are described for some interesting accelerator applications.

The foundations of many of the subdisciplines of radiological protection laid in accelerator laboratories began with the invention of accelerators. This paper suggests that the discipline of accelerator radiological protection has played and will continue play a more significant part in our lives than is generally recognized. A brief review of some existing uses of accelerators by society is given, and a few probable future uses are described. These future applications will result in the exposure of accelerator (or {open_quotes}mixed{close_quotes}) radiation fields to an increased population. Consequently, what are perceived to be the rather specialized concerns of today`s accelerator health physicists will -- by necessity -- become of general interest to all health physicists.

Acceptance criteria for corroded low temperature, low pressure carbon steel piping containing weld defects is presented along with a typical application of these criteria. They are intended to preclude gross rupture or rapidly propagating failure due to uniform wall thinning, local wall thinning, pitting corrosion and weld defects. The minimum allowable uniform wail thickness is based on the code-of-record allowable stress and fracture criteria. Weld defects are postulated as potential sites for fracture initiation. CEGB/R6 failure assessment diagram is used as the fracture criteria to determine the minimum allowable wall thickness. Design of a large portion of the low temperature, low pressure piping is dominated by axial stresses. Existing local wall thinning acceptance criteria address high pressure piping where hoop stress dominates the design. The existing criteria is over conservative, in some cases, when used on low pressure piping. Local wall thinning criteria is developed to limit the axial stress on the locally thinned section, based on a reduced average thickness. Limits on pit density are also developed to provide acceptance criteria for pitted piping.