High-frequency acoustics of He-3 in aerogel

High-frequency (similar to 15 MHz) acoustics were performed on He-3 in 98% porous silica aerogel using an acoustic cavity technique. Measurements of t he sound attenuation in the normal Fermi liquid and superfluid display beha vior quite different from the bulk owing to strong elastic scattering of qu asiparticles. The transition from first-to-zero sound is completely obscure d with a quasiparticle mean-free path estimated to be in the range of 200-3 00 nm. No collective mode attenuation peak was observed at or below the sup erfluid transition.