Experimental investigation of the diffusion of slow electrons in nitrogen and hydrogen

Abstract

This paper presents the results of precise measurements of the diffusion of slow electrons in hydrogen and nitrogen in the presence of a uniform electric field. Such measurements lead directly to the value of Townsend’s energy coefficient ( k T ) as a function of Z/p (field strength/gas pressure). Since the drift velocity ( W ) of the electrons is also known (Nielsen & Bradbury 1936), the following physical quantities are deduced as functions of Z/p : mean free path of the electrons at unit pressure, mean energy lost by an electron per collision and the collisional cross-sections of the molecules. Measurements of the diffusion were obtained from two apparatuses which differed in dimensions and metal of the electrodes. The range of gas pressures employed was 3 to 14 mm of mercury. A table shows that the values of k T as a function of Z/p derived from these measurements agree (with one exception) to within 3%, and it is therefore considered that the measurements are trustworthy. The results are presented graphically and in tabular form.