Cold Neutron Prompt Gamma-Ray Activation Analysis for Characterization of Hydrogen Storage and Related Materials
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0927-EE03-05
Cold Neutron Prompt Gamma-Ray Activation Analysis for Characterization of Hydrogen Storage and Related Materials Rick Paul Analytical Chemistry Division, National Institute of Standards and Technology, 100 Bureau Drive, STOP 8395, Gaithersburg, Maryland, 20899 ABSTRACT Prompt gamma-ray activation analysis (PGAA) is an important technique for analyzing materials that may impact the hydrogen economy. An instrument for cold neutron PGAA, located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of hydrogen and other elements in a variety of such materials. The detection limit for hydrogen is less than 10 mg/kg for most materials. PGAA has been used to characterize materials with potential for hydrogen storage (e.g. single wall carbon nanohorns, lithium magnesium imides, and zirconium beryllium hydrides), to measure hydrogen uptake by solid proton conductors, and to characterize stoichiometries of Nafion films used as membranes in fuel cells. Future upgrades to the instrument will improve detection limits, applicability, and user interface.
INTRODUCTION The U. S. government has placed strong emphasis on creating and expanding the hydrogen economy. Establishing such an economy means overcoming many obstacles, particularly in the areas of hydrogen storage, hydrogen delivery, and fuel cell development. State-of-the-art materials for hydrogen storage currently do not satisfy the guidelines issued to make a commercially useful hydrogen storage system for competitive hydrogen-powered transportation. One key to improving the state of the art of these materials is to develop a detailed understanding of the elemental composition and impurities that may enhance or detract from the hydrogen storage capacities. Prior to the widespread use of hydrogen as a fuel for automobiles, an infrastructure for delivery of hydrogen to fueling stations must be established. Delivery through pipelines is most efficient, however this may result in hydrogen embrittlement of metal pipelines that are not specifically designed for hydrogen. A thorough investigation of the enbrittlement problem requires methods for nondestructive determination of hydrogen at low levels in metals. Finally, efficient design of fuel cells requires optimizing the composition of materials used for cell membranes. Methods are also needed to diagnose problems in fuel cells, such as leaching of contaminants into cell membranes during fuel cell operation. Prompt gamma-ray activation analysis is a nondestructive multi-elemental analysis technique that is suitable for many of these applications. When samples are irradiated in a beam of neutrons, nuclei of many elements undergo neutron capture and emit prompt gamma rays during de-excitation. Measurement of the energies and intensities of these gamma rays yields quantitative and qualitative analysis. Although PGAA is capable of measuring most elements, it is particularly useful for the
determination of light elements (e.g. H, B, N, C) that are not easily measurable by other techni
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