Lawrence Livermore National Laboratories Research Articles

Investigation of Factors That Affect the Sensitivity of Accelerator Mass Spectrometry for Cosmogenic 10Be and 26Al Isotope Analysis

We report experiments designed to improve accelerator mass spectrometry (AMS) of (10)Be and (26)Al for a wide range of geological applications. In many cases, the precision of the AMS isotope ratio measurement is restricted by counting statistics for the cosmogenic isotope, which are in turn limited by the intensity of AMS stable ion beam currents. We present data obtained at the Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratories (LLNL) indicating that AMS ion beam currents are impacted by certain elemental impurities. For (10)Be analysis, the AMS ion beam current is most adversely affected by the presence of titanium (which can be challenging to separate chemically during sample preparation because of its tendency toward stable refractory forms) and aluminum (which can coelute with beryllium during cation exchange chromatography). In order to minimize impurities that suppress AMS ion beam currents, we evaluate, using inductively coupled plasma atomic emission spectroscopy (ICP-AES), a widely used chemical separation protocol involving a multiacid digestion scheme, preseparation elemental analysis, anion exchange chromatography, ad hoc selective precipitation, cation exchange chromatography, and postseparation elemental analysis.

FANTM: First Article NIF Test Module

Designing and developing the 1.7- to 2.1-MJ power conditioning system (PCS) that power the flashlamps of the main and power amplifiers for the National Ignition Facility (NIF) lasers is one of several responsibilities assumed by Sandia National Laboratories (SNL) and Maxwell Physics International in support of the NIF Project. The NIF is currently being constructed at Lawrence Livermore National Laboratories (LLNL). The test facility that evolved over three years to satisfy the project requirements is called the First Article NIF Test Module (FANTM). It was built at SNL and operated for about 17000 shots to demonstrate component performance expectations over the lifetime of NIF. A few modules are used initially in the amplifier test phase of the project. The final NIF system requires at least 192 modules in the four capacitor bays. The paper briefly summarizes the final design of the FANTM facility and compares its performance with the predictions of circuit simulations for both normal operation and fault-mode response. Applying both the measured and modeled power pulse waveforms as input to a LLNL amplifier gain code indicates that the 20-capacitor PCS can satisfy the NIF requirement for an average gain coefficient of 5.00%/cm and can exceed 5.20%/cm with 24 capacitors.

WebWise: guide to the joint genome institute web site.

This installment of the WebWise series reviews the Joint Genome Institute (JGI) web site (http://www.jgi.doe.gov/). The JGI, established in 1997 (Casey 1996), represents an ongoing consolidation of the U.S. Department of Energy (DOE) genome sequencing centers established at the Los Alamos (LANL), Lawrence Berke ley (LBNL) , and Lawrence Livermore National Laboratories (LLNL). The JGI web site presents a centralized information center to disseminate information pertaining to the sequencing efforts still being carried out at the three laboratories while a new central research facility is being built. Many of the data links lead to pages that are actually still hosted by these three research laboratories. This review is intended to summarize the consolidated JGI web resource; pages hosted by LANL, LBNL, or LLNL are indicated on the site map displayed in Figure 1. However, the site map does not attempt to represent all of the information available at the LANL, LBNL, or LLNL web sites (http://www-ls.lanl.gov/; http://www-hgc.lbl.gov/; http://wwwb i o . l l n l . g o v / b b r p / g e n o m e / g e nome.html). The site map (Fig. 1) is intended to provide a simple road map to data and tools pages. Therefore, it does not include all of the links provided on the JGI site map; redundant links as well as some groupings of related links are depicted as a single link on the site map. The main features of this web site, as well as the features of those sites already reviewed, are indicated in Table 1. As with the previous WebWise reviews, you may find it useful to point your Browser window to the JGI web site while reading.

In Situ Decontamination of Soil

Abstract Methods for decontamination of soil in situ are receiving increased attention, as the requirement to clean these sites has become a national concern. The continual and costly liability is an important corporate incentive to clean contaminated soils. The development of an effective technology for in situ decontamination is a priority issue. Some in situ decontamination processes are similar to enhanced oil recovery schemes and use an integrated heating approach. One such method consists of heating by conduction and convection in conjunction with electrical heating. Advantages of electrical heating are that the energy can be focussed and the soil heated uniformly. The integrated heating approach has been extensively tested in the United States in a joint venture between Lawrence Livermore National Laboratories (LLNL) and the University of California at Berkeley. The most significant test was done at an abandoned Naval Air Base, now named the LLNL Gasoline Spill Site. It has been demonstrated that such an integrated approach can remove hydrocarbon contaminates from in situ at an accelerated rate. The objective of this paper is to present a mathematical model that solves the heat transfer problem for the integrated heating process. The model is also used to investigate the practicality of the process in terms of energy requirements and the time it takes to clean the soil. The mathematical model combines all of the principal heat transfer mechanisms of the process. These are electrical heating, convection, conduction and accumulation of energy. In addition, conductive heat losses from the sides and bottom of the heated volume and the substantial variation of electrical resistivity with temperature are included. Calculations made using the mathematical model developed in this paper are in good agreement with results obtained with the general-purpose reservoir simulator, TETRAD. Introduction Increasing the temperature of a contaminated soil helps in the removal of the hydrocarbons. The introduction of heat increases the solubility of the hydrocarbon with the water phase, increases equilibrium concentrations in the vapour phase and causes easier desorption from the clay mineral. These factors can accelerate the clean up process several times(1). Some proposed methods consider an integrated heating approach, consisting of heating by conduction and convection at the same time as heating electrically(2, 3). This approach has been successfully tested in the United States by Lawrence Livermore National Laboratories (LLNL) at the LLNL Gasoline Spill Site(2, 4). At this site, hydrocarbons have accumulated in situ and are in communication with the ground water system. Vertical injection/production wells completed with electrodes are strategically located to heat the soil. The heating of the soil is primarily by steam injection. The electrical heating is supplemental and is used to heat regions where the steam will not flow. The estimated cost to clean the contaminated soil(2), which has an area of about 2,000 m2 and is 15 m thick is of the order of $(CDN) 50/m3. The electrical heating component of the above process is limited because of the use of vertical electrodes spaced far apart. The current density at the electrode surface is large and decreases rapidly with distance.

Lasers in materials processing

We analyze the general requirements for an economically viable laser materials-processing application. Laser light is not only expensive relative to other forms of energy but at ∼ $10/kg of product for laser processing costs (corresponding to one 2 eV photon per product molecule) it is expensive relative to most bulk chemicals. We identify four criteria for a successful application that allows efficient utilization of this costly source of energy. In reviewing the status of uranium laser isotope separation (LIS) at the Lawrence Livermore National Laboratories (LLNL), we show how this program satisfies our criteria.