The coefficient of absorption of sound in liquid helium has been measured at a frequency of 11.8 Mc/sec in the temperature range from 0.2°K to 1°K, at vapor pressure, and at 8.0, 13, and 18.3 atmospheres. Careful measurements above 0.9°K at vapor pressure reveal that the two sharp maxima observed by Chase and Herlin at the top of their absorption curve were an instrumental effect. Preliminary results at the higher pressures indicate that, if allowance is made for the pressure variation of the density and the velocity of sound, the attenuation decreases exponentially with pressure at temperatures just below 1°K.

• Received 15 August 1956

DOI:https://doi.org/10.1103/PhysRev.105.38