Abstract
We have measured by the phonon echo technique the ultrasonic attenuation in an adsorbed 4He film on silica powder as a function of pressure at 35 MHz and low temperatures. The attenuation curves present the typical shape of a multilayer adsorption isotherm of type II according to the Brunauer, Emmett, Teller (BET) classification and the Frenkel–Halsey–Hill (FHH) slab theory may be used to describe the attenuation in the adsorbed film. This is important because the adsorption isotherm cannot be obtained by the traditional technique on a powder with small specific surface.
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