The evaluation of the accuracy, precision and lower detection limits of the determination of trace radionuclides in environmental samples can become quite sophisticated and time consuming. This in turn could add significant cost to the analyses being performed. In the present method, a {open_quotes}deficit reduction approach{close_quotes} has been taken to keep costs low, but at the same time provide defensible data. In order to measure the accuracy of a particular method, reference samples are measured over the time period that the actual samples are being analyzed. Using a Lotus spreadsheet, data are compiled and an average accuracy is computed. If pairs of reference samples are analyzed, then precision can also be evaluated from the duplicate data sets. The standard deviation can be calculated if the reference concentrations of the duplicates are all in the same general range. Laboratory blanks are used to estimate the lower detection limits. The lower detection limit is calculated as 4.65 times the standard deviation of a set of blank determinations made over a given period of time. A Lotus spreadsheet is again used to compile data and LDLs over different periods of time can be compared.

The positron decay partial half-lives of {sup 143}Pm and {sup 144}Pm are needed to assess the viability of elemental Pm as a cosmic-ray clock. We have conducted experiments to measure the {beta}{sup +} branches of these isotopes; we find {beta}{sup +} branches of these isotopes; we find {beta}{sup +} branches of <5.7 {times}10{sup {minus}8} for {sup 143}Pm and <8{times}10{sup {minus} 7} for {sup 144}Pm. Through these branches are a factor of 20 lower than the previous experimental limits, the resulting partial half-lives are still too uncertain to permit any firm conclusions.

The positron decay partial half-lives of [sup 143]Pm and [sup 144]Pm are needed to assess the viability of elemental Pm as a cosmic-ray clock. We have conducted experiments to measure the [beta][sup +] branches of these isotopes; we find [beta][sup +] branches of these isotopes; we find [beta][sup +] branches of <5.7 [times]10[sup [minus]8] for [sup 143]Pm and <8[times]10[sup [minus] 7] for [sup 144]Pm. Through these branches are a factor of 20 lower than the previous experimental limits, the resulting partial half-lives are still too uncertain to permit any firm conclusions.

We carried out essentially all the carbon cycle modeling calculations that were required by the IPCC Working Group 1. Specifically, IPCC required two types of calculations, namely, ``inverse calculations`` (input was CO{sub 2} concentrations and the output was CO{sub 2} emissions), and the ``forward calculations`` (input was CO{sub 2} emissions and output was CO{sub 2} concentrations). In particular, we have derived carbon dioxide concentrations and/or emissions for several scenarios using our coupled climate-carbon cycle modelling system.

A dynamic simulator of the TOPAZ II reactor system has been developed for the Nuclear Electric Propulsion Space Test Program. The simulator combines first-principle modeling and empirical correlations in its algorithm to attain the modeling accuracy and computational through-put that are required for real-time execution. The overall execution time of the simulator for each time step is 15 ms when no data is written to the disk, and 18 ms when nine double precision data points are written to the disk once in every time step. The simulation program has been tested and it is able to handle a step decrease of $8 worth of reactivity. It also provides simulations of fuel, emitter, collector, stainless steel, and ZrH moderator failures. Presented in this paper are the models used in the calculations, a sample simulation session, and a discussion of the performance and limitations of the simulator. The simulator has been found to provide realistic real-time dynamic response of the TOPAZ II reactor system under both normal and casualty conditions.

Earthquake events are well-known to prams a variety of empirical scaling laws. Accordingly, renormalization methods offer some hope for understanding why earthquake statistics behave in a similar way over orders of magnitude of energy. We review the progress made in the use of renormalization methods in approaching the earthquake problem. In particular, earthquake events have been modeled by previous investigators as hierarchically organized bundles of fibers with equal load sharing. We consider by computational and analytic means the failure properties of such bundles of fibers, a problem that may be treated exactly by renormalization methods. We show, independent of the specific properties of an individual fiber, that the stress and time thresholds for failure of fiber bundles obey universal, albeit different, staling laws with respect to the size of the bundles. The application of these results to fracture processes in earthquake events and in engineering materials helps to provide insight into some of the observed patterns and scaling-in particular, the apparent weakening of earthquake faults and composite materials with respect to size, and the apparent emergence of relatively well-defined stresses and times when failure is seemingly assured.

The L3 detector, located at the LEP storage ring at CERN (European Center for Nuclear Research), has recently installed a silicon microvertex detector (SMD). The purpose of the SMD is to enhance the tracking capabilities of L3 and to provide increased vertex measurement precision for tagging b-jets in the search for the Higgs boson, when LEP doubles its center of mass energy for the LEP 200 running. The subject of this article is the fabrication and testing of the front-end electronics for the SMD. The article is organized into several sections. The first section describes the SMD, the second section discusses the front-end electronics, the third section presents the testing procedures and the results of the tests.

High-order harmonic generation provides a new method for generating coherent, XUV radiation. These harmonics are characterized by a rapid, pertubative drop at low orders, followed by a broad plateau extending to photon energies of 150 eV in the lighter, rare gas atoms. An experimentally observed limit coincides with the theoretical limit for harmonic generation in neutral atoms given by the expression E{sub c}(eV)=IP(0)+3U{sub p}(I), where E{sub c} is the energy cutoff of the harmonic plateau, IP(O) is the field-free ionization potential and U{sub p} is the electron quiver energy at the maximum intensity, I seen by the atom. As part of an effort to develop this technique into a general purpose XUV source, extensive work to understand the phase-matching between the harmonic and driving fields, and the resulting effect on the conversion efficiency, angular distribution and spectral brightness has been undertaken at several. Though, certain aspects of the harmonically generated radiation such as the polarization, relative strength of a given harmonic, and the plateau extent, are defined by the single atom-field interaction. Specifically, the single-atom harmonic spectrum is determined primarily by the interaction of a driven, quasi-free electron with the atomic potential. Using two, independent fields one can affect the …

A long term goal of soft x-ray imaging has been to make ultrahigh resolution images of unstained, unprepared, wet, live biological microstructures in physiological normal environments. This is now being accomplished with features as small as 300 {Angstrom} being observed in two dimensional x-ray images. While this achievement is remarkable, most complex biological structures are three dimensional in nature and will require three dimensional images on the few hundred Angstrom scale for the structure-function studies required by modern biology. We have been endeavoring to achieve this three dimensional capability with soft x-ray techniques.

A project is in progress that addresses two of the problems with existing holdup measurement technology: the need for compact instrumentation and a more efficient means of reducing the massive amounts of data to quantities of Special Nuclear Materials (SNM). The approach taken by the project utilizes the Miniature Modular MultiChannel Analyzer (M{sup 3}CA), a complete and truly portable gamma-ray spectroscopy system, under development at Los Alamos National Laboratory. The hardware is then integrated and automated by the Holdup Measurement System II (HMSII) software being developed by the Oak Ridge Y-12 Plant. Together they provide the hardware components, measurement control in the field, automated data acquisition, data storage and manipulation which simplify holdup measurements.

The authors report the first observation of optically pumped stimulated emission from an GaN epilayer at 77K and at room temperature grown by reactive ion-beam molecular beam epitaxy. The observed uv optical emission profile was a nonlinear function of the pump power density, with line narrowing at threshold power densities. The similarity in the emission profile as compared with those of films grown with low-pressure metal-organic chemical vapor deposition and metal-organic vapor phase epitaxy techniques will be noted.

We have used the 2-D PIC code, GYMNOS, to study the transient behaviors in the Heavy Ion Fusion (HIF) injectors. GYMNOS simulations accurately provide the steady state Child-Langmuir current and the beam transient behavior within a planar diode. The simulations of the LBL HIF ESAC injector experiments agree well with the experimental data and EGUN steady state results. Simulations of the nominal HIF injectors have revealed the need to design the accelerating electrodes carefully to control the ion beam current, particularly the ion loss at the end of the bunch as the extraction voltage is reduced.

Applying the tools of algorithmic information theory, we compare several candidates for an asymptotically machine-independent. absolute measure of the informational or cognitive'' distance between discrete objects x and y. The maximum of the conditional Kolmogorov complexities max[l brace]K(y[vert bar]z) K(m[vert bar]y)[r brace], is shown to be optimal, in the sense of being minimal within an additive constant among semicomputable, symmetric, positive semidefinite functions of z and y satisfying a reasonable normalization condition and obeying the triangle intequality. The optimal metric, in turn, differs by at most an additive logarithmic term from the size of the smallest program for a universal reversible computer to transform x into y. This program functions in a 'catalytic'' capacity, being retained in the computer before, during, and after the computation. Similarly, the sum of the conditional complexities. K(y[vert bar]x) + K(x[vert bar]y), is shown to be equal within a logarithmic term to the minimal amount Of information flowing out and in during a reversible computation in which the program is not retained. Finally. using the physical theory of reversible computation, it is shown that the simple difference K(x) - K(y) is an appropriate (ie universal, antisymmetric, and transitive) measure of the amount of thermodynamic work …

Applying the tools of algorithmic information theory, we compare several candidates for an asymptotically machine-independent. absolute measure of the informational or ``cognitive`` distance between discrete objects x and y. The maximum of the conditional Kolmogorov complexities max{l_brace}K(y{vert_bar}z) K(m{vert_bar}y){r_brace}, is shown to be optimal, in the sense of being minimal within an additive constant among semicomputable, symmetric, positive semidefinite functions of z and y satisfying a reasonable normalization condition and obeying the triangle intequality. The optimal metric, in turn, differs by at most an additive logarithmic term from the size of the smallest program for a universal reversible computer to transform x into y. This program functions in a `catalytic`` capacity, being retained in the computer before, during, and after the computation. Similarly, the sum of the conditional complexities. K(y{vert_bar}x) + K(x{vert_bar}y), is shown to be equal within a logarithmic term to the minimal amount Of information flowing out and in during a reversible computation in which the program is not retained. Finally. using the physical theory of reversible computation, it is shown that the simple difference K(x) - K(y) is an appropriate (ie universal, antisymmetric, and transitive) measure of the amount of thermodynamic work required to transform string x into …