Zusammenfassung
We have measured the laminar friction of various diluted 3 He- 4 He mixtures, of natural 4 He and of isotopically pure 4 He on an oscillating sphere below 1 K. For 3 He concentrations x 3 ranging from 10 −2 to 10 −4 we find a reduction of the drag above 0.5 K when compared to the pure liquid and a large enhancement below, which is almost independent of x 3 . At low concentrations 5·10 −5 >x 3 ...
Zusammenfassung
We have measured the laminar friction of various diluted 3 He- 4 He mixtures, of natural 4 He and of isotopically pure 4 He on an oscillating sphere below 1 K. For 3 He concentrations x 3 ranging from 10 −2 to 10 −4 we find a reduction of the drag above 0.5 K when compared to the pure liquid and a large enhancement below, which is almost independent of x 3 . At low concentrations 5·10 −5 >x 3 ≥5·10 −7 the drag becomes proportional to x 3 which implies a transition from a hydrodynamic to a ballistic regime. This is confirmed by deducing the mean free path of the 3 He atoms from the data. The temperature dependence of the drag in the ballistic regime, however, is found to be proportional to T and therefore different from the expected T 1/2 behaviour.
Altmetric