Search NASA⌕ Search

Engineering topics

Williamson, Todd L.

Publications and source records attributed to Williamson, Todd L..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Observation of carbon fractionation in HE debris by large geometry secondary ion mass spectrometry

Detonation of high explosives (HE) is an exothermic process producing a variety of simple gaseous molecules (e.g. CO, CO 2 , N 2 , H 2 O) and solid carbon soot. The chemistry of formed carbon soot is influenced by the high pressures (P) and temperatures (T) induced by shock compression that occurs due to detonation. This can result in isotopic fractionation of the soot as the lighter 12 C is more likely to participate in reactions forming gaseous products, resulting in 13 C enriched particulate soot material. Isotopic analysis of HE soot is usually performed at the bulk level of an agglomerated sample, which gives an average value of HE derived soot and other bystander debris and can obscure trends among individual particles. To study C isotopic fractionation of HE debris at the individual particle level, we have used Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS), which has the ability to deliver in-situ high precision and accuracy isotope ratios of individual particles. This allows for evaluating thousands of individual particles from HE detonations, providing isotopic data at the per particle level. HE debris particles from a variety of detonation conditions (P ranging from 25 – 85 GPa) have been measured by LG-SIMS showing a general trend of higher 13 C fractionation with increasing P.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Plutonium particle analysis by LG-SIMS and LA-MC-ICP-MS for environmental safeguards

During nuclear facility inspections, International Atomic Energy Agency (IAEA) inspectors collect dust particles using cotton swipes. Analysis of these swipes is an extremely powerful tool with which to confirm treaty compliance or identify treaty violations. Through particle analysis it is possible to identify individual particles representative of nuclear activities. Uranium particle analysis is a reasonably mature technique used by IAEA and its Network of Analytical Laboratories for treaty verification. However, the IAEA has recently identified the maturation of plutonium and mixed uranium-plutonium particle analysis techniques as a top priority. We propose to address this area directly by developing the new methods necessary to analyze samples containing plutonium and mixed uranium-plutonium particles. The end products of this study will be: (A) more accurate and ultra-precise isotopic characterization of plutonium -bearing particles from environmental swipe samples, and (B) development and validation of laser ablation particle analysis techniques as robust and accurate analysis methodologies for future safeguards missions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Synthesis and characterization of dense Gd 2 Ti 2 O 7 pyrochlore thin films deposited using RF magnetron sputtering

Thin films of phase-pure pyrochlore Gd 2 Ti 2 O 7 have been synthesized by RF magnetron sputtering. The films were prepared from oxide targets in 50% O 2 /Ar atmosphere and deposited on 111 yttria-stabilized zirconia (YSZ) substrates at a temperature of 800 °C. The pyrochlore structure was confirmed via grazing angle X-ray diffraction and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) analysis also showed that the films were dense and of uniform thickness with surface roughness of approximately 8 nm. The total conductivity measured with AC impedance spectroscopy was found to be independent of thickness and comparable in magnitude to that of bulk Gd 2 Ti 2 O 7 . Differences were observed in the Arrhenius behavior between the bulk and thin film samples and are attributed to varying states of order in the crystalline lattice compounded by different levels of background impurities.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Editors' Choice—Field Trials Testing of Mixed Potential Electrochemical Hydrogen Safety Sensors at Commercial California Hydrogen Filling Stations

Hydrogen safety sensors must meet specific performance requirements, mandated by the U.S. Department of Energy, for hydrogen fueling station monitoring. Here, we describe the long-term performance of two zirconia-based mixed potential electrochemical hydrogen gas sensors, developed specifically with a high sensitivity to hydrogen, low cross-sensitivity, and fast response time. Over a two-year period, sensors with tin-doped indium oxide and strontium doped lanthanum chromite electrodes were deployed at two stations in four field trials tests conducted in Los Angeles. The sensors documented the existence of hydrogen plumes ranging in concentration from 100 to as high as 2700 ppm in the area surrounding the dispenser, consistent with depressurization from 700 bar following vehicle refueling. As expected, the hydrogen concentration reported by the mixed potential sensors was influenced by wind direction. Baseline stability testing at a Chino, CA station showed no measureable baseline drift throughout 206 days of uninterrupted data acquisition. In conclusion, the high baseline stability, excellent correlation with logged fueling/depressurization events, and absence of false alarms suggest that the zirconia-based mixed potential sensor platform is a good candidate for protecting hydrogen infrastructure where frequent calibrations or sensor replacement to reduce the false alarm frequency have been shown to be cost prohibitive.

08 HYDROGEN↗