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An investigation of the dispersion of excitations in a quantum liquid, superfluid He4, is carried out. An attempt is made to systematize the published experimental data that indicate a substantially different nature of excitations with wave vectors corresponding to different parts of the dispersion curve of liquid He4. Neutron spectroscopy data are analyzed in relation to a certain physical hypothesis concerning the formation of such a spectrum, and it is found that the majority of the known experimental facts can be explained in framework of that hypothesis. Particular attention is paid to a comparison of the experimental data obtained on the DIN-2PI time-of-flight spectrometer (at the IBR-2 Reactor, Dubna) with the results obtained at foreign research centers.

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Analytical forms of the empirical equations of state of the system are obtained for an equimolar He3–He4 mixture in the homogeneous liquid and dense fluid phases at temperatures 1.5–14 K and pressures 0–10 MPa on the basis of the existing experimental P–V–T data. This is done by choosing approximating expressions, setting up a computer program, and calculating the fitting coefficients of the expressions. The quality of the approximation corresponds to the accuracy of the experimental determinations and is on average 0.5%.