In order to study the antiferromagnetic (AFM) spin structure near the interface of exchange-biased bilayers, polarized neutron diffraction measurements were performed on a series of (111) Co(7.5 nm)/CoO(X nm) and CoO(X nm) thin films where X = 20, 40 and 100 nm. In these samples, field cooling through the Neel temperature of the AFM increases the component of the CoO moment perpendicular to the applied field, relative to the parallel component. The subsequent application of a 500 Oe field perpendicular to the cooling direction rotates both the Co and CoO moments. Experiments on CoO films without Co showed a smaller difference between the parallel and perpendicular CoO moments in response to cooling and applied fields. Exchange coupling between the Co and CoO layers is apparently responsible for the increased projection of the AFM moments perpendicular to the cooling field.

The Advanced Photon Source at Argonne National Laboratory has implemented a number of methods for people to interact with the accelerator systems. The accelerator operators use Sun workstations running MEDM and WCL to interface interactively with the accelerator, however, many people need to view information rather than interact with the machine. One of the most common interfaces for viewing information at the Advanced Photon Source is the World Wide Web. Information such as operations logbook entries, machine status updates, and displays of archived and current data are easily available to APS personnel. This interface between people and the accelerator has proven to be quite useful. Because the Intranet is operating-system independent and inherently unidirectional, ensuring the prevention of unauthorized or accidental control of the accelerators is straightforward.

We have studied magnetic field penetration and vortex line formation in a [Nb(100 {angstrom})/Si(15 {angstrom})]x20 multilayer by magnetization and polarized neutron reflection. With the magnetic field applied parallel to the surface, the magnetization revealed the presence of a kink above H{sub cl} indicative of transitions between one row of fluxoids and two rows of fluxoids parallel to the surface. The spin-dependence of neutron reflectivity below H{sub cl} was consistent with a penetration depth of 1200 {angstrom}, substantially larger than that of bulk Nb. In the mixed phase (H{sub ext} > H{sub cl}) the field was found to penetrate the surface, with a slope as found in the case of H{sub ext} < H{sub cl}. At H{sub ext} > H{sub cl} vortex forms in addition to surface penetration. A modulation of the vortex fields was found with the periodicity of the Nb/Si bilayers as evidenced by the spin dependence of the reflectivity at the first Bragg peak of the multilayer.

The data acquired in the Parkfield, California experiment are unique and they are producing results that force a new look at some conventional concepts and models for earthquake occurrence and fault-zone dynamics. No fault-zone drilling project can afford to neglect installation of such a network early enough in advance of the fault-zone penetration to have a well-defined picture of the seismicity details (probably at least 1000 microearthquakes--an easy 2-3 year goal for the M<0 detection of a borehole network). Analyses of nine years of Parkfield monitoring data have revealed significant and unambiguous departures from stationarity both in the seismicity characteristics and in wave propagation details within the S-wave coda for paths within the presumed M6 nucleation zone where we also have found a high Vp/Vs anomaly at depth, and where the three recent M4.7-5.0 sequences have occurred. Synchronous changes well above noise levels have also been seen among several independent parameters, including seismicity rate, average focal depth, S-wave coda velocities, characteristic sequence recurrence intervals, fault creep and water levels in monitoring wells. The significance of these findings lies in their apparent coupling and inter-relationships, from which models for fault-zone process can be fabricated and tested with time. The more general …

The APS accelerator control system is a typical modern system based on the standard control system model, which consists of operator interfaces to a network and computer-controlled interfaces to hardware. The network provides a generalized communication path between the host computers, operator workstations, input/output crates, and other hardware that comprise the control system. The network is an integral part of all modern control systems and network performance will determine many characteristics of a control system. This paper describes the methods used to provide redundancy for various network system components as well as methods used to provide comprehensive monitoring of this network. The effect of archiving tens of thousands of data points on a regular basis and the effect on the controls network will be discussed. Metrics are provided on the performance of the system under various conditions.

Nuclear safeguards and nonproliferation rely on nondestructive analytical tools for prompt and noninvasive detection, verification, and quantitative analysis of nuclear materials in demanding environments. A new tool based on the detection of correlated neutrons in narrow time windows is being investigated to fill the niche created by the current limitations of the existing methods based on polyethylene moderated {sup 3}He gas proportional tubes. Commercially produced Boron-loaded ({sup 10}B) plastic scintillating fibers are one such technology under consideration. The fibers can be configured in a system to have high efficiency, short neutron die-away, pulse height sensitivity, and mechanical flexibility. Various configurations of the fibers with high density polyethylene have been considered which calculationally result in high efficiency detectors with short die-away times. A discussion of the design considerations and calculations of the detector efficiency, die-away time, and simulated pulse height spectra along with preliminary test results are presented.

The MINOS (Main Injector Neutrino Oscillation Search) long-baseline experiment will search for neutrino oscillations by measuring an intense {nu}{sub {mu}} beam at the end of a 730 km flight path. The 10,000 ton MINOS far detector will utilize magnetized steel plates interleaved with track chambers to reconstruct event topologies and to measure the energies of the muons, hadrons and electromagnetic showers produced by neutrino interactions. The experiment is designed to detect {nu}{sub {mu}} {r_arrow} {nu}{sub {tau}} and {nu}{sub {mu}} {r_arrow} {nu}{sub e} oscillations with {Delta}m{sup 2} {ge} 0.001 eV{sup 2} and sin{sup 2} (2{theta}) {ge} 0.01. Any oscillation signal observed can be verified and studied by several independent tests: a near/far rate comparison, the NC/CC event ratio, the CC and NC event energy spectra, and the identification of electrons and {tau} leptons. The neutrino beam can be operated in both wide-band and narrow-band configurations, allowing the detailed study oscillation phenomena. The experiment is scheduled to begin operation in 2001.

A brief survey of E0 strength in a number of nuclei in different regions of the nuclear chart is presented. The connection between E0 strength and shape coexistence is reviewed. Nuclear structure information obtained from measurements of electric monopole transitions in {sup 184}Pt and {sup 187}Au is discussed. Plans for future experiments utilizing radioactive ion beams and E0 internal pair formation is presented.

Article on the potential energy surfaces for the reaction of O atoms with CH3I and implications for thermochemistry and kinetics.

Laser-induced fluorescence is used to image the central plane of the mix region of two immiscible liquids subject to the Rayleigh-Taylor instability. The familiar bubbles and spikes display a complex internal structure. This small-scale structure creates a large contact area whose density is constant in time. The size of the mixing zone, defined in a new way, grows with coefficient ab >= 0.054.

The US Home Team has investigated the physics and engineering issues for two alternate poloidal field coil configurations for ITER. The first is called the Segmented CS configuration, where all of the solenoid modules are pancake-wound. The second option, termed the Hybrid CS configuration, utilizes a layer-wound central module and pancake-wound end modules. Performance comparisons are presented for the baseline design and the two alternate PF configurations, characterizing the 21 MA reference scenario. Alternate operating modes such as reverse-shear operation and a 17 MA driven mode were evaluated, but are not reported here.

As part of the United States Department of Energy`s (DOE) Comprehensive Test Ban Treaty (CTBT) research and development effort, a Knowledge Base is being developed. This Knowledge Base will store the regional geophysical research results as well as geographic contexual information and make this information available to the Automated Data Processing (ADP routines) as well as human analysts involved in CTBT monitoring. This paper focuses on the initial development of a browser prototype to be used to interactively examine the contents of the CTBT Knowledge Base. The browser prototype is intended to be a research tool to experiment with different ways to display and integrate the datasets. An initial prototype version has been developed using Environmental Systems Research Incorporated`s (ESRI) ARC/INFO Geographic Information System (GIS) product. The conceptual requirements, design, initial implementation, current status, and future work plans are discussed. 4 refs., 2 figs.

Seismic responses of the Zion nuclear power generation complex accounting for structure-to-structure interaction effects as predicted by CLASSI and FLUSH Codes are presented in this paper. Two aspects of the multi-structure analyses were considered: the effect of structure-to-structure interaction on structure response and the variability in structure response as predicted by different codes, including structure-to-structure interaction. The effect of structure- to-structure interaction on the response of the Zion reactor building and AFT complex (the auxiliary/fuel-handling/turbine building complex) was assessed by comparing the results of CLASSI analyses with and without interaction between structures. The results show that the reactor building has a very small effect on the AFT complex, but the effect of structure-to-structure interaction on the reactor building from the AFT complex is substantial. A comparison of the reactor building`s response as predicted by CLASSI and FLUSH, structures including structure-to-structure interaction, shows significant differences. Modeling three-dimensional configuration of a complicated power plant structure such as the Zion`s with equivalent two-dimensional models for structure-to-structure interaction analysis requires careful consideration.

We compare the thermo-elastic-plastic response of fissionable metals calculated by the solid mechanics code DYNA to an analytic model for the case of a uniformly heated thin spherical shell and to experimental data for the case of a thin rod heated in a pulsed reactor. In both cases, the materials are volumetrically heated by neutron exposure. We find good agreement between the code and the analytic model and experimental data for the first and second case, respectively. For very fast heating times, macroscopic displacement may be replaced by microscopic plastic flow. To verify this behavior, an experiment to be done at SNLA SPR III is described. Validation of the code in these simple geometries is a necessary step if calculations involving more complicated geometries are to be understood and trusted.

A roughly chronological account is given of Arthur N. Coxs published work of 1953-1996 in, mostly, stellar pulsation theory, with a digression into stellar opacity. When possible, his work is placed in the context of the contemporary efforts.

By replacing the magnets and vacuum chamber for the 3 GeV SPEAR II storage ring, the natural emittance of the machine can be reduced from 130 to 18 nm-rad and the stored current can be raised from 100 to 200 mA with a 50 h lifetime. This configuration increases focused photon flux for insertion device beamlines by an order of magnitude and the photon brightness for future undulators would exceed 10{sup 18} at 5 keV. Due to a higher critical energy, the photon flux in the 20 keV range for bending magnet beamlines increases by more than two orders of magnitude. We present preliminary SPEAR III design study results and plans to implement the facility upgrade with minimal downtime for SSRL users.

There has been much progress in the development of high intensity lasers and in the science of laser driven inertially confined fusion such that ignition is now a near term prospect. This lecture reviews the field with particular emphasis on areas of my own involvement.

Trace Pu{sup 239} and Am{sup 241} contamination on a surface whose alpha count is dominated by U{sup 235} and U{sup 234} decay has been successfully quantified by counting swipes in external alpha spectroscopy chambers. The swipe process, however, is labor intensive and subject to uncertainties in the swiping process as well as degraded spectral resolution due to the presence of the swipe material. A multichannel instrument for automated in situ measurements of interior and exterior contamination has been developed which incorporates a rotary table, 13 fixed ion-implanted silicon detectors, and spectroscopy electronics. Custom software was written to allow alpha spectrometer to function as a virtual instrument in the LabView environment. This system gives improved speed and resolution as well as a complete log of the location of areas of high surface contamination, a feature not practical to obtain by other methods, and one which opens the possibility of long term studies such as Pu outgrowth evaluation employing the instrument. The authors present performance data as well as system integration, calibration, control, and dynamic geometric efficiency calculations related to the design of this and next generation systems.

This paper discusses the design and testing results of a resonant accelerometer developed for integrated surface-micromachining processes.First- and second-generation designs are presented. The sensors use leverage mechanisms to transfer force from a proof mass to double-ended tuning fork (DETF) resonators, used as force transducers. Each fork forms the basis of an integrated oscillator to provide the output waveforms. The DETF`s on the first-generation device have a nominal frequency of 175 kHz, and the sensor has a measured scale factor of 2.4 Hz/g. The oscillators on this device exhibit a root Allan variance floor of 38 mHz (220 ppb). The second-generation, higher-sensitivity sensor uses DETF`s with a nominal frequency of 68 kHz and has measured a scale factor of 45 Hz/g.

Gas-filled hohlraums are presently the base line ignition target design for the National Ignition Facility. Initial Nova experiments on gas-filled hohlraums showed that radiation temperature was reduced due to SBS and SRS scattering losses and that implosion symmetry had shifted compared with vacuum hohlraums and calculations. Subsequent single beam experiments imaging thermal x-ray emission showed the shift is due to laser-plasma heating dynamics and filarnentation in a flowing plasma. Experiments using a single beam have shown that scattering losses and effects of filamentation are reduced when the beam is smoothed with an random phase plate (RPP) or kinoform phase plate (KPP). Scattering is further reduced to less than 5% of the incident laser energy when SSD is added.

Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported in [l]. The Nova laser is used to generate a 10-15 Mbar shock at the interface of a two-layer planar target, which triggers perturbation growth, due to the Richtmyer-Meshkov and Rayleigh-Taylor instabilities as the interface decelerates. This resembles the hydrodynamics of the He-H interface of a Type II supernova at intermediate times, up to a few x10{sup 3} s. The experiment is modeled using the hydrodynamics codes HYADES and CALE, and the supernova code PROMETHEUS. Results of the experiments and simulations are presented. New analysis of the bubble velocity is presented, as well as a study of 2D vs. 3D difference in growth at the He-H interface of SN 1987A.

Fission energy systems that significantly reduce the need for the user country to be involved in the nuclear operations and technology could simplify implementation and reduce the proliferation potential. Conceptual system designs with improved (relative to the once-through LWR fuel cycle) proliferation resistance for application in developing countries are being evaluated. The fission energy systems being studied include all activities and equipment necessary to produce energy, recycle selected materials, and dispose of the waste. The systems currently being studied are required to function with no refueling of the reactors on the user site. These requirements are being used to initiate the study, on the assumption that removal of these operations from within the developing countries will improve the proliferation resistance. Preliminary evaluations of a small fast reactor core cooled either by sodium or lead-bismuth are provided.