SummaryA detailed account is given of the solution to the problems associated with the use of the Townsend-Huxley method of measuring the ratio of drift speed to diffusion coefficient for very low energy electron swarms. The elimination of radial components of the electric field within the diffusion chamber is shown to be the major experimental problem, especially in the case of the comparatively weak electric fields which must be used for some of the measurements in the near· thermal region. The experimental techniques and procedures, which are described in some detail, enable measurements to be made in this region with an accuracy comparable to that which has been achieved at higher electron energies. I. INTRODUOTIONOne of the methods of examining collision phenomena between low energy electrons and gas molecules is to measure the ratio of the drift velocity W to the diffusion coefficient D of an electron swarm moving under the influence of an electric field E in a gas at a pressure p. Since WjD is a pressure-dependent quantity, the experimental results are always given either in terms of DjfL, where fL is defined as the ratio WjE, or of kv a parameter closely related to the Townsend energy factor, k T , which is defined as the ratio of the mean energy of agitation of the electrons to the mean thermal energy of the molecules of the gas through which the electron swarm moves. These quantities are related by the expression whereBoth k1 and DjfL are functions of the ratio EjN and are also, in general, functions of the gas temperature.An examination of a number of possible sources of error in the TownsendHuxley method for measuring k1 has been made by Crompton and Jory (1962), who showed that, by careful attention to the choice of experimental parameters and conditions, results with errors of less than I % can be achieved for measurements of k1 in hydrogen at 293°K over the range in E jp of O· 1-5·0 V cm -1 torr-I, for which the lowest value of k1 is approximately 2. If the measurements are to be extended to lower values of E jp, the data lose much of their significance unless

No abstract

The performance of a capacitance manometer operated at 300 °C is described. Calibration against a deadweight primary pressure standard indicates that the stability over a period of 3 months is better than 0.25% of the measured pressure over the pressure range 15–1000 Torr (2.04–131.6 kPa).

No abstract