III. RÉFRIGÉRATEURS A DILUTION ET TRANSFERTS DE CHALEUR
SOME PROPERTIES OF LIQUID He³ He⁴ SOLUTIONS AND ITS CRYOGENIC APPLICATION (REVIEW OF RECENT RUSSIAN WORKS)

Abstract
The method of getting low temperatures by dilution of He³ in He⁴ is considered in the first part of the review. The next dilution refrigerators are described : the Neganov's continuous and Peshkov's single-cycle dilution refrigerator for getting 5 m° K and Zinovyeva's refrigerator for getting 10-25 m° K. The second part of the review considers some recent works concerning the properties of He³He⁴ solutions. Zinovyeva's results of measurements of Kapitza resistance Rk are presented and discussed. The measurements of Rk between a solid and liquid He⁴, He³ and their solutions of concentration of 1 % and 5,5 % are carried out in temperature interval 0,05° - 1,3° K. The Kapitza resistance Rk below 0,3-0,4° K is the same for all studied liquids and specimens and proportional to T^-3. Rk does not depend strongly on the material of samples and the state of interface. The unusual behaviour of surface tension of dilute solutions is discussed. The maxima on the temperature dependence curves, discovered by Boldarev and Zinovyeva, confirm the validity of Andreev's hypothesis about the existence of new levels localized near the surface for impurity excitations with ε₀ = 1,7° K and µ = 0,9 M. The measurements of fourth sound velocity in concentrated solutions fulfilled by Dyumin, Eselson et al, are described. The authors estimate the energetic spectrum parameters of rotons and impurity excitations and present the concentration dependence Ɗ of rotons and M/m He³ of impurity excitations.