NONLINEAR SCATTERING AND ATTENUATION OF FIRST SOUND IN SUPERFLUID 4He AT HIGH FREQUENCY AND TEMPERATURE NEAR T_λ

The attenuation coefficient of the impressed first sound due to the scattering of random background of the second sound is calculated. The result shows that this is an important factor which gives rise the attenuation of the first sound in the vicinity of transition temperature T_λ at very high frequencies of GHz range. The predicted value agrees with the measured data in order of magnitude.