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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Article
  • Peer Reviewed
UCLA Journal of Environmental Law and Policy, Volume 8, Issue 2 (1989)
[No abstract]
    Cover page: <em>Robertson v. Methow Valley Citizens Council</em> and the New "Worst Case Analyis" Regulation
    • Article
    • Peer Reviewed
    Program on International Migration (2020)
      Cover page: Constructing and contesting state-urban borders: litigation over Refugee Reception Offices in post-apartheid South African cities
      • Thesis
      • Peer Reviewed
      UC Berkeley Electronic Theses and Dissertations (2012)

      Mercury, a potent neurotoxin, is a global environmental problem. New mercury sensing technologies are needed to meet the expanding demands on the mercury observation network. We demonstrate the utility of gold nanoparticles as a stand-alone, inexpensive, and sensitive mercury monitor. Gold nanoparticles display a peak in the visible range of their UV-vis absorbance spectra due to localized surface plasmon resonance (LSPR). The energy of this resonance is affected by adsorption of mercury. Isolated individual gold nanorods with an average length and diameter of 60 and 20 nm saturate after adsorption of 4 attograms of elemental mercury, and produce a 3 nm blue shift in their LSPR, with the shift dependent on the surface-area-to-volume ratio and aspect ratio. A modified Gans theory model predicts the shift at saturation given the particle dimensions if saturation occurs with 45% monolayer coverage.

      Nanoparticle films on a transparent substrate show potential as a practical and robust method for sensing low levels of mercury vapor. The adsorption of 15 atoms of Hg causes a 1 nm shift in the LSPR wavelength of 5 nm gold spheres. The rate of shift in the peak absorbance is linear with mercury concentrations from 1 to 825 µgHg/mair3. The speed of the sensor response is limited by diffusive mass transfer and can be enhanced by optimizing the sample flow characteristics. We modeled the diffusive mass transfer and optimized the sample delivery accordingly. Regeneration of the sensing films, done by heating to 160°C, allows for repeatable measurements on the same film.

        Cover page: Mercury Sensing with Optically Responsive Gold Nanoparticles
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2019)
        We designed and tested a compact deuteron-deuteron fusion neutron generator for application to 40Ar/39Ar geochronology. The nearly monoenergetic neutrons produced for sample irradiation are anticipated to provide several advantages compared with conventional fission spectrum neutrons: Reduction of collateral nuclear reactions increases age accuracy and precision. Irradiation parameters within the neutron generator are more controllable compared with fission reactors. Confidence in the prediction of recoil energies is improved, and their likely reduction potentially broadens applicability of the dating method to fine-grained materials without vacuum encapsulation. Resolution of variation in the 39K(n,p)39Ar neutron capture cross section at 1.3 to 3.2 MeV and discovery of a strong resonance at ~2.4 MeV illuminate future pathways to improve the technique for 40Ar/39Ar dating.
          Cover page: Boutique neutrons advance <sup>40</sup>Ar/<sup>39</sup>Ar geochronology.
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2018)
          A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58 × 107 n/cm2/s ± 5% (approximately 3 × 108 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.
            Cover page: Design, construction, and characterization of a compact DD neutron generator designed for 40Ar/39Ar geochronologyCreative Commons 'BY-NC-ND' version 4.0 license
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