RUI: Acoustic Loss Evaluation of Metals for Ultralow Temperature Gravity Wave Detectors (Physics)

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The mechanical quality factor (Q) of low-loss metallic alloys and elements will be studied at temperatures from 50 mK to 4 K and at a frequency of about 1 kHz. Material selection will be based on anticipated suitability for use for ultralow temperature Weber-bar gravity wave detectors. The currently favored material for planned detectors is aluminum 50-56 alloy, but alternate materials exhibit superior bondability, thermal conductivity and density. There are practically no ultralow temperature Q-data on these materials, and it is urgently needed to assess their suitability for constructing large-scale detectors. Qs will be obtained from the measured time constants of decay of free vibrations of small mechanical resonators mounted in a dilution refrigerator cryostat. Materials to be investigated include copper alloys, aluminum alloys, and transition element metals. Experimental studies will emphasize careful metallurgical characterization and systematic elimination of extrinsic contributions to measured quality factors. In addition to supporting gravity wave detector development, it is expected that the results will contribute to the fundamental understanding of mechanical loss mechanisms in metals at ultralow temperatures.