Sound propagation in liquid He in impurity-helium solids
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The observed features of the attenuation of ultrasound in ImHe samples created after the introduction of impurity particles [formula omitted] in a volume of helium II show that a porous substance consisting of a loosely interconnected continuous network is created. It is formed by impurity particles encapsulated in solidified helium. The propagation of ordinary sound in these porous samples is similar to the fast sound mode in light aerogels. The temperature dependence of the attenuation for different ImHe samples is investigated. It is established that the character of the attenuation in [formula omitted] samples is considerably different from that in heavier ImHe solids [formula omitted] Analysis of the attenuation leads to the conclusion that ImHe samples have a wide distribution of pores, from 8 nm to 800 nm. The study of ultrasound in helium in ImHe samples near the point shows the presence of broadening in the attenuation peak as compared with bulk liquid helium. The suppression of [formula omitted] is very small, 0.2 mK. 2000, American Institute of Physics. All rights reserved.
