[en] The method of streaming rays are expanded to two spatial dimensions (three-phase space dimensions, x, y, and s) and used as a basis for development of the electron-transport computer code SR2D. The streaming-ray algorithm is a Eulerian-Lagrangian hybrid. Electrons are followed as they traverse the medium along specified streaming rays. Fluxes, however, are computed at the centers of the fixed cells. The development of the SR2D code required the specification of a Lagrangian-streaming ray network overlaying a three-dimensional Eulerian grid. In contrast to its one-dimensional predecessor, the SR2D code accommodates non-uniform cell sizes and allows for arbitrary quadrature sets (S₂, S₄, S₆, S₈, S₁₂, or S₁₆). The critical aspect of the streaming ray method is the determination of the path lengths of each and every streaming ray through all of the Eulerian cells. These values must be precalculated and stored because of the iterative nature of the solution scheme. Although the number of pathlengths may be exceedingly large, computer memory requirements are minimized, however, in the two dimensional algorithm by the symmetry of the geometry in each pathlength increment. The SR2D code was used to calculate the energy-deposition profile for two kinds of sources, an isotropic point source and a monodirectional point at the periphery of a two-dimensional medium

[en] We have made a comprehensive evaluation of the standard theory of primordial nucleosynthesis, by (a) determining the nuclear reactions most important for light element production in the Big Bang; (b) conducting a detailed study of the rates and uncertainties of these reactions (c) employing a Monte Carlo analysis to properly evaluate uncertainties in the computed elemental abundances arising from reaction rate uncertainties; and (d) comparing the predicted abundances of d, ³He, ⁴He, and ⁷Li to those inferred from observations. We find a consistent agreement for 2.68 x 10^-10 ≤ η ≤ 3.77 x 10^-10, where η is the baryon-to-photon ratio, thereby supporting the standard Big Bang nucleosynthesis (SBBN) theory. The corresponding constraint on the baryon density parameters is 0.01 ≤ Ω_b ≤ 0.09, where the primordial d+³He (⁴He) abundance sets the lower (upper) bound. We find that the new reaction rates increase the η upper bound from ⁷Li by 45%, and that inconsistencies in SBBN will arise if the primordial ⁴He mass fraction is less than 0.237 or if the primordial ⁷Li abundance is at the Pop I level. For slightly non-standard primordial nucleosynthesis models, comparisons to primordial abundances show that the number of neutrino families N_nu is limited to N_nu ≤ 3.3. Specifically, 3.5 neutrino families (3 Dirac ν's plus one Majorana ν) or more are ruled out at the 2-σ level. The dependence of the N_nu upper limit on the abundances limits has been parameterized

[en] The Daresbury Recoil Separator (DRS) has been installed for nuclear astrophysics research at Oak Ridge National Laboratory's Holifield Radioactive Ion Beam Facility. It will be used for direct measurements of capture reactions on radioactive ions which occur in stellar explosions such as novae, supernovae and X-ray bursts. These measurements will be made in inverse kinematics with radioactive heavy ion beams incident on hydrogen and helium targets, and the DRS will separate the capture reaction recoils from the intense flux of beam particles. Details of the new DRS experimental equipment and preliminary results from the first commissioning experiments with stable beams are described, along with the plans for the first measurements with radioactive beams. Other astrophysics research efforts at ORNL--in theoretical astrophysics, nuclear astrophysics data evaluation, heavy element nucleosynthesis, theoretical atomic astrophysics, and atomic astrophysics data--are also briefly described

[en] The potential for understanding spectacular stellar explosions such as novae, supernovae, and X-ray bursts will be greatly enhanced by the availability of the low-energy, high-intensity, accelerated beams of proton-rich radioactive nuclei currently being developed at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. These beams will be utilized in absolute cross section measurements of crucial (p, γ) capture reactions in efforts to resolve the substantial qualitative uncertainties in current models of explosive stellar hydrogen burning outbursts. Details of the nuclear astrophysics research program with the unique HRIBF radioactive beams and a dedicated experimental endstation--centered on the Daresbury Recoil Separator--will be presented

[en] A graphical debugger for combinatorial geometry being developed at Oak Ridge National Laboratory is described. The prototype debugger consists of two parts: a FORTRAN-based ''view'' generator and a Microsoft Windows application for displaying the geometry. Options and features of both modules are discussed. Examples illustrating the various options available are presented. The potential for utilizing the images produced using the debugger as a visualization tool for the output of the radiation transport codes is discussed as is the future direction of the development

[en] An efficient, high-resolution, vertical-focusing, Bragg crystal x-ray spectrometer has been specifically designed and constructed for use in measurements of x rays produced in collisions of energetic heavy ions. In this report the design and resulting operational characteristics of the final instrument are fully described. A wide variety of sample data is also included to illustrate the utility of this device in several areas of research. 14 refs., 38 figs

[en] This study investigates motor-operated globe valve (MOV) performance in a liquid sodium environment as reported to the Centralized Reliability Data Organization (CREDO) from site representatives at several liquid metal reactors and liquid metal test facilities. The CREDO data base contains engineering histories for 179 motor-operated glove valves. Thirty nine failures have been documented for these components in over 8.7 million hours of operation. The most common MOV events were anomalies with the limit and torque switches, although human initiated problems were also frequent causes of failures. The failure data suggest that an improved preventive maintenance program with a higher frequency of inspection of the limit and torque switches should increase MOV availability and reliability. The event rate for all failure modes was computed as 4.47 events per 10⁸ operating hours by assuming a Poisson distribution of failure over valve operating time. The 5% and 95% confidence limits based on a chi-squared (χ²) probability distribution function were computed as 3.36 and 5.83 events per 10⁶ operating hours, respectively. The operating performance of these liquid metal MOVs was compared to similar data for MOVs in commercial light water reactors and was found to exhibit similar failure rates

[en] Nuclear hardening capabilities of US and foreign ground force systems is a primary concern of the Department of Defense (DoD) and US Army. The Monte Carlo Adjoint Shielding Code System -- MASH v1.0 was developed at Oak Ridge National Laboratory (ORNL) to analyze these capabilities, i.e. the shielding effectiveness, for prompt radiation from a nuclear weapon detonation. Rapidly changing world events and the proliferation of nuclear weapons related technology have increased the kinds of nuclear threats to include intentionally dispersed radiation sources and fallout from tactical nuclear weapons used in the modern AirLand battlefield scenario. Consequently, a DoD area of increasing interest focuses on determining the shielding effectiveness of foreign and US armored vehicles to radiological warfare and fallout radiation threats. To demonstrate the applicability of MASH for analyzing dispersed radiation source problems, calculations have been completed for two distributed sources; a dispersed radiation environment simulated by a uniformly distributed ⁶⁰Co source, and a ²³⁵U fission weapon fallout source. Fluence and dose assessments were performed for the free-field, the inside of a steel-walled two-meter box, in a phantom standing in the free-field, and in a phantom standing in the two-meter box. The results indicate substantial radiation protection factors for the ⁶⁰Co dispersed radiation source and the fallout source compared to the prompt radiation protection factors. The dose protection factors ranged from 40 to 95 for the two-meter box and from 55 to 123 for the mid-gut position of the phantom standing in the box. The results further indicate that a ⁶⁰Co source might be a good first order approximation for a tactical fission weapon fallout protection factor analysis

[en] Steam distillation methods are commonly used to prepare Kjeldahl digests for N stable isotope analysis. Steam distillation requires skilled operation of specialized equipment as well as considerable operator time, and is subject to sample cross contamination unless precautionary washing procedures (which further increase sample preparation time) are adopted. A simple, inexpensive, labor saving diffusion method for Kjeldahl digests using disposable polypropylene specimen containers (128 mL) with threaded lids was devised to overcome problems with steam distillation. Diffused ammonia was collected in a disposable test tube (12 by 75 mm) containing an acid trap. Fractionation of N stable isotopes was <1% for diffused diluted simulated Kjeldahl digests, even when <20% of the initial NH₃ present was diffused. As diffusion becomes more complete isotope fractionation decreases. Direct comparison of aliquots of the same plant tissue Kjeldahl digest by steam distillation and diffusion over a wide range of ¹⁵N enrichments (0.36-43.3 atom %) indicated that deviation of the two methods was about 1%. The ¹⁵N enrichment of diffused samples was consistently slightly less than that of steam distilled samples. The method is recommended for research using ¹⁵N enriched or depleted sources, but not for research measuring natural variation in ¹⁵N abundance, unless complete diffusion is assured

[en] Information about the US Nuclear Reaction Data Network (USNRDN) such as its members, work in progress, summaries of meetings, and organizational details may be found in its WWW Homepage. This paper is an overview of the data support provided by the network for basic research in nuclear astrophysics, radioactive ion beams, high energy heavy-ion and electron interactions and related activities involving all aspects of data stewardship