We have been investigating the application of acoustic resonance spectroscopy as a noninvasive method to monitor changes in gas composition and pressure in sealed containers. Our work is motivated by observations that, under some conditions, interim or long-term storage of plutonium-containing metal, oxide, or residues within hermetically sealed containers may result in pressure buildup and changes in gas composition. In our experiments a drum-like gas cavity is formed within a cylindrical container. Sound waves are excited using a piezoelectric transducer mounted on the outside of the container. The frequency response spectrum contains a series of peaks whose positions and widths depend upon the composition of the gas and the geometry of the cylindrical resonator; the intensities vary with the gas pressure. Comparing the frequency of observed gas resonances with theory gives excellent agreement. Small changes in gas composition, better than 1:1000, are readily measurable.
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