Investigation of ultrasound attenuation in impurity-helium solids containing liquid helium.

The attenuation of ultrasound in Impurity-Helium. (Im-He) solids created up on introduction of impurity atoms or molecules (D-2, N-2, Kr) into a volume of superfluid helium has been investigated. The observed features of atten uation show that a porous substance consisting of a loosely interconnected continuous network is created in superfluid helium. This network is formed by impurity particles encapsulated in solidified helium. Analysis of attenu ation allows us to conclude that Im-He solid samples have a wide distributi on of pores from 8 nm to 800 nm. It was established that the character of o f attenuation in D-2-He samples is considerably different from that in heav ier Ina-Hf solids, Sor which two maxima of attenuation were sometimes obser ved. A sharp peak was observed at T(c)o very close to the bulk helium lambd a transition temperature and a second broad peak occurred at T-c<T(c)o. Thi s behavior is similar to that predicted theoretically for liquid helium in restricted fractal porous media.