Engineering topics
Williams, R. M.
Publications and source records attributed to Williams, R. M..
Development of a Low-Level Ar-37 Calibration Standard
Argon-37 is an important environmental signature of an underground nuclear explosion. Producing and quantifying low-level 37Ar standards is an important step in the development of sensitive field measurement instruments for use during an On-Site Inspection, a key provision of the Comprehensive Nuclear-Test-Ban Treaty. This paper describes progress at Pacific Northwest National Laboratory (PNNL) in the development of a process to generate and quantify low-level 37Ar standard material, which can then be used to calibrate sensitive field systems at activities consistent with soil background levels. The 37Ar used for our work was generated using a laboratory-scale, high-energy neutron source to irradiate powdered samples of calcium carbonate. Small aliquots of 37Ar were then extracted from the head space of the irradiated samples. The specific activity of the head space samples, mixed with P10 (90% stable argon:10% methane by mole fraction) count gas, is then derived using the accepted Length-Compensated Internal-Source Proportional Counting method. Due to the low activity of the samples, a set of three Ultra-Low Background Proportional-Counters designed and fabricated at PNNL from radio-pure electroformed copper was used to make the measurements in PNNL’s shallow underground counting laboratory. Very low background levels (<10 counts/day) have been observed in the spectral region near the 37Ar emission feature at 2.8 keV. Two separate samples from the same irradiation were measured. The first sample was counted for 12 days beginning 28 days after irradiation, the second sample was counted for 24 days beginning 70 days after irradiation (the half-life of 37Ar is 35.0 days). Both sets of measurements were analyzed and yielded very similar results for the starting activity (~0.1 Bq) and activity concentration (0.15 mBq/ccSTP argon) after P10 count gas was added. A detailed uncertainty model was developed based on the ISO Guide to the Expression of Uncertainty in Measurement. This paper presents a discussion of the measurement analysis, along with assumptions and uncertainty estimates.
Shielding concepts for low-background proportional counter arrays in surface laboratories
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Electrochemical deposition of semiconductors for thermoelectric devices
Thermoelectric microgenerators are an approach to power conversion which can deliver milliwatts to watts of power at a few to several tens of volts.
Semiconductor nanowires for thermoelectric devices
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Metallurgical examination of an AMTEC power unit
Two AMTEC power units fabricated by Advanced Modular Power Systems, Inc. using a cold end condenser manufactured by Creare, Inc. which operate for 342 hours and 575 hours were dissected and examined.
Reactivity of thin metal films on sodium beta alumina ceramic in high temperature, low pressure sodium vapor
Electrochemical techniques including impedance spectroscopy are routinely used to test the performance of AMTEC electrodes.
Mathematical modeling of the impedance of single and multi-tube AMTEC units
AMTEC power systems are designed for use on extended space missions. During the lifetime of such missions the power available for the spacecraft will depend on the degradation of the system performance. Development of a tool that allows monitoring of the system degradation will provide an aid in dtermining the condition of the power source.
Challenges facing successful development of long life, high temperature, high efficiency/power AMTECs for space applications
The technical challenges confronting development of Alkali Metal Thermal-to Electric Converters (AMTEC) for up to 15 year life on NASA Mars and outer planetary missions are significant, although approaches to solutions are understood by many investigators.
Advances in electrode materials for AMTEC
An improved electrode for the Alkali Metal Thermal to Electric Converter (AMTEC) has been made and tested.
Electrochemical deposition of novel semiconductors for thermoelectric devices
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The Sodium Exposure Test Cell to Determine Operating Parameters for AMTEC Electrochemical Cells
The Sodium Exposure Test Cell (SETC) is a non-power producing cell which has been developed to evaluate and test components of the electrochemical cell in an Alkali Metal Thermal to Electric Converter.
A Quantitative Model for the Exchange Current of Porous Molybdenum Electrodes on Sodium Beta-Alumina in Sodium Vapor
This paper presents a model of the exchange current developed for porous molybdenum electrodes on sodium beta-alumina ceramics in low pressure sodium vapor, but which has general applicability to gas/porous metal electrodes on solid electrolytes.
Sodium Transport Modes in AMTEC Electrodes
Transport of alkali metal atoms through porous cathodes of alkali metal thermal-to-electric converter (AMTEC) cells is responsible for significant, reducible losses in the electrical performance of these cells.
The Mars oxidant experiment (MOx) for Mars '96
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants.
Lifetime and Performance of Titanium Nitride Electrodes in AMTEC Cells
AMTEC, The Alkali Metal Thermal to Electric Converter, is a direct energy conversion device capable of near-Carnot efficiencies.
A Quantitative Tunneling/Desorption Model for the Exchange Current at the Porous Electrode/Beta - Alumina/Alkali Metal Gas Three Phase Zone at 700-1300K
The exchange current observed at porous metal electrodes on sodium or potassium beta -alumina solid electrolytes in alkali metal vapor is quantitatively modeled with a multi-step process with good agreement with experimental results.