MEASUREMENT OF LATERAL DIFFUSION COEFFICIENTS AND FIRST TOWNSEND COEFFICIENTS FOR ELECTRONS IN HELIUM BY AN ELECTRON-DENSITY SAMPLING METHOD

Direct experimental measurements of electron diffusion coefficients D in helium have been carried out at 300°K in the range of 0<~EN<2.7×10-16 V cm2 (0<~EP0<10 V cm-1 Torr-1) by an improved electron-density sampling method. Absolute errors less than ± 0.5% are claimed in the range 0<~EN<9×10-17 V cm2 and less than 1.5% in the range 9×10-17<EN<2.7×10-16 V cm2. The obtained values of D are in agreement with those of Crompton, Elford, and Jory in the range of 2.124×10-19<~EN<~3.03×10-17 V cm2 studied by these authors. Also measurements of αW (where α is Townsend's first coefficient and W the drift velocity) have been performed in the range 9.03×10-17<~EN<~2.6×10-16 V cm2 (corresponding to 3.2<~EP0<~10 V cm-1 Torr-1). Values of α with an accuracy evaluated at ± 10% are obtained by dividing αW by the W values found in the literature. These α values are to be compared with those of the literature, which are dispersed by a factor of 3 in the above range. © 1969 The American Physical Society.