Diffusion in Gaseous Helium at Low Temperatures

The repulsive interaction of atoms in S states

“…The success of this function can best be seen from table 2. The fit with the scattering results is satisfactory, but (10) is substantially below the variational estimates, particularly at lao. This seems unavoidable although the discrepancy is in fact much less than that in the He + He interaction at the same distance, using the Sakamoto and Ishiguro calculations.…”

Symmetry Effects in Gas Kinetics. I. The Helium Isotopes

“…This was substantiated later for He 3 by van Kranendonk, Compaan, and de Boer, 6 and in greater detail in the recent extensive calculations of Kilpatrick et al & In connection with the gaseous viscosity of the He isotopes, measurable effects below 3°K were shown to occur by Buckingham and Temperley, 7 de Boer and Cohen, 8 and Buckingham and Scriven. 9 These are discussed in detail in later sections.…”

“…where a = 1/77!, 7= 1/T7 12 , 0= (5/6.4 12 *)y 9 and c= (a-7)/ (/5+I7). The quantity A12* is here the ratio of two collision integrals closely connected with diffusion of the two types of atom; in magnitude it is not far from unity.…”

“…These results have been calculated by using an interatomic potential of the form where /W=/i^6(l+^-2)-/ 2 ,-(-i), (9) f x =a/{a(l+b)-6-Sb{, / 2 l+(l+6)/i, and the parameters a, b have been assigned the values 13.5, 0.2, respectively. For He 4 , even-order phases using this type of potential have been given by Buckingham, Hamilton, and Massey, 12 and for He 3 they have been calculated by Scriven and Buckingham, 13 in each case for values of K sufficient to give the viscosity up to 5°K.…”

“…9 Figure 3 shows how the viscosity of the mixture depends on the molar fraction of He 3 present, for temperatures up to 5°K. The same values of the potential parameters, A m and e//c, have been used as before.…”