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25. Mobilities of he ions in liquid helium
S 140
SHORT COMMUNICATIONS
24. E x p e r i m e n t s on e v a p o r a t i o n of i o n s i n l i q u i d h e l i u m II. G. CARERI, U. FASOLI and F. GAETA. Istituto di Fisica, Universit~ di Padova, Italy. The current due to the m o v e m e n t of positive or negative ions produced by a rays through the liquid-vapour interface, has been measured as a function of voltage and temperature in liquid nitrogen and liquid helium II. The results in liquid nitrogen indicate an accumulation of charges on the surface layer, which reduces the ionic current one would observe under similar situation in the bulk liquid; this interphase current is rather insensitive to temperature changes and the same behaviour is shown for both the positive and negative ions. In liquid helium instead a sharp dependence on the temperature is observed, and the behaviour is quite different for the positive and negative particles. These results are consistent with and can be explored in the same framework as the ion heat-flush experiments.
25. M o b i l i t i e s of H e I o n s i n L i q u i d H e l i u m . LOTHAR MEYER and F. REIF. Institute for the Study of Metals, Chicago, Illinois, U.S.A. The mobilities of positive and negative ions in liquid helium have been measured between 1.2 and 4.2°K and fields of 50-200 Volt/cm. The mobilities are field independent and increase very rapidly below the )t-point. Below 2°K the temperature dependence of the positive ion mobility is similar to the reciprocal of the density of the normal fluid; in the range above 2°K, the positive ion mobility is approximately inversely proportional to the viscosity of the liquid. The mobility of the negative ions is less than that of the positive ions and the ratio of the mobilities depends somewhat on temperature. These results differ from those of W i l l i a m s 1) and C a r e r i 2) who found the mobilities strongly field dependent. This discrepancy is probably due to the fact that for very low field strengths the ions always remain practically at thermal energies. 1) Williams, R. C., Canad. J. Phys. 35 (1957) 134. 2) Careri, el al, Program 5th International Confereuce on Low Temperature Physics, Madison, Wisconsin, August 1957, p. 79.
26. T h e v i s c o s i t y of Hquid h e l i u m b e t w e e n I.I°K and 0.79°K. A. D. B. WOODS and A. C. HOLLIS HALLETT. D e p a r t m e n t of Physics, University of Toronto, Canada. A rotating cylinder viscometer has been used in a booster cryostat to measure the viscosity of liquid helium I I b~tween 1.1°K and 0.78°K. The results show t h a t the viscosity rises rapidly with decreasing temperature in this range, in qualitative agreement with the L a n d a u and K h a l a t n i k o v theory. Quantitatively the viscosity at 0.74°K was measured to be 175 4- 10 p poise and this compares favourably with the theoretical value of 173/z poise at 0.8°K.
27. V i s c o s i t y of L i q u i d H e l i u m II n e a r t h e L a m b d a P o i n t . J. G. DASH Royal Society Mond Laboratory, Cambridge, England.
*).
The theory of Landau and Khalatnikov for the viscosity of liquid He II is examined in the neighborhood of the lambda point. Arguments are advanced against the validity *) Guggenheim Fellow 1957-8, on leave from Los Alamos Scientific Laboratory.
SHORT COMMUNICATIONS
24. E x p e r i m e n t s on e v a p o r a t i o n of i o n s i n l i q u i d h e l i u m II. G. CARERI, U. FASOLI and F. GAETA. Istituto di Fisica, Universit~ di Padova, Italy. The current due to the m o v e m e n t of positive or negative ions produced by a rays through the liquid-vapour interface, has been measured as a function of voltage and temperature in liquid nitrogen and liquid helium II. The results in liquid nitrogen indicate an accumulation of charges on the surface layer, which reduces the ionic current one would observe under similar situation in the bulk liquid; this interphase current is rather insensitive to temperature changes and the same behaviour is shown for both the positive and negative ions. In liquid helium instead a sharp dependence on the temperature is observed, and the behaviour is quite different for the positive and negative particles. These results are consistent with and can be explored in the same framework as the ion heat-flush experiments.
25. M o b i l i t i e s of H e I o n s i n L i q u i d H e l i u m . LOTHAR MEYER and F. REIF. Institute for the Study of Metals, Chicago, Illinois, U.S.A. The mobilities of positive and negative ions in liquid helium have been measured between 1.2 and 4.2°K and fields of 50-200 Volt/cm. The mobilities are field independent and increase very rapidly below the )t-point. Below 2°K the temperature dependence of the positive ion mobility is similar to the reciprocal of the density of the normal fluid; in the range above 2°K, the positive ion mobility is approximately inversely proportional to the viscosity of the liquid. The mobility of the negative ions is less than that of the positive ions and the ratio of the mobilities depends somewhat on temperature. These results differ from those of W i l l i a m s 1) and C a r e r i 2) who found the mobilities strongly field dependent. This discrepancy is probably due to the fact that for very low field strengths the ions always remain practically at thermal energies. 1) Williams, R. C., Canad. J. Phys. 35 (1957) 134. 2) Careri, el al, Program 5th International Confereuce on Low Temperature Physics, Madison, Wisconsin, August 1957, p. 79.
26. T h e v i s c o s i t y of Hquid h e l i u m b e t w e e n I.I°K and 0.79°K. A. D. B. WOODS and A. C. HOLLIS HALLETT. D e p a r t m e n t of Physics, University of Toronto, Canada. A rotating cylinder viscometer has been used in a booster cryostat to measure the viscosity of liquid helium I I b~tween 1.1°K and 0.78°K. The results show t h a t the viscosity rises rapidly with decreasing temperature in this range, in qualitative agreement with the L a n d a u and K h a l a t n i k o v theory. Quantitatively the viscosity at 0.74°K was measured to be 175 4- 10 p poise and this compares favourably with the theoretical value of 173/z poise at 0.8°K.
27. V i s c o s i t y of L i q u i d H e l i u m II n e a r t h e L a m b d a P o i n t . J. G. DASH Royal Society Mond Laboratory, Cambridge, England.
*).
The theory of Landau and Khalatnikov for the viscosity of liquid He II is examined in the neighborhood of the lambda point. Arguments are advanced against the validity *) Guggenheim Fellow 1957-8, on leave from Los Alamos Scientific Laboratory.