Abstract
The effect on ultrasonic attenuation in superconductors of 'Andreev' scattering-the scattering of electronic excitation by spatial variations of the order parameter is investigated. The result at small ql (q is the sound wavevector and l the electron mean free path) agrees with previous theoretical work, whereas that at large ql shows a new and unusual dependence of attenuation on Andreev and impurity scattering rates. The applicability of this theory to clean type II superconductors near Hc1 and Hc2 is discussed.