The Townsend Coefficients for Ionization by Collision in Pure and Contaminated Hydrogen as a Function of the Cathode Material

The Townsend coefficients for ionization by collision were measured for pure mercury-free hydrogen and for hydrogen contaminated with sodium and NaH vapor. Cathodes of platinum and sodium and NaH-coated platinum were used. The values of αp at values of X/p below 300 are found to be smaller for pure hydrogen than for hydrogen contaminated with mercury vapor. The values of αp for hydrogen contaminated with sodium and NaH are as much as twice as great as those for pure hydrogen at the lower values of X/p. The curve of αp plotted as a function of X/p, for this case, shows a sharp peak at an X/p of 350. This peak indicated the presence of some substance which is ionized by the excitation of hydrogen. The curves of βα and γ for the platinum cathode plotted as functions of X/p show peaks at the lower values of X/p which are analogous to those shown by Bowls. The curves for the NaH cathode show a narrow but remarkably high peak at an X/p of 10. There are also several lower peaks but no general rise for the NaH cathode. These peaks indicate relatively large photoemission effects (Θηgα) at the cathodes at the lower values of X/p. In the case of the platinum cathode at the higher values of X/p the curves show a general rise caused by electron emission due to the bombardment of the cathode by positive ions. The values of βα and γ for the sodium surfaces are much smaller than in the case of platinum for the higher values of X/p indicating that these surfaces are relatively poor emitters under positive ion bombardment. In the course of the work it was possible, in most cases, to measure a sparking potential at the conclusion of the experimental work at each value of X/p. These data for the sparking potentials give curves which agree fairly well with the experimental curves as derived by Ehrenkranz. From the values found for the γ-coefficient, the sparking potentials were calculated and these potentials gave sparking potential curves which are in rough agreement with the experimentally derived curves of Ehrenkranz.