Experimental determination of the Landau-Placzek ratio for liquid helium to the λ line

The measurements relate to high pressures and to the scattering of light of wavelength 0.488 mu m through 90 degrees . The observed Landau Placzek ratio is shown to be in good agreement with the best available values of gamma -1 ( gamma =Cp/Cv), both above and below the lambda point, provided that mod T-Tlambda mod >0.3 mK. For smaller temperatures differences the ratio is observed to fall below gamma -1 and to remain finite and probably continuous through the lambda line. The results are not in good quantitative agreement with those of other authors, and the reason for the discrepancy is discussed.