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 $\frac{\alpha }{p}$ at values of $\frac{X}{p}$ below 300 are found to be smaller for pure hydrogen than for hydrogen contaminated with mercury vapor. The values of $\frac{\alpha }{p}$ for hydrogen contaminated with sodium and NaH are as much as twice as great as those for pure hydrogen at the lower values of $\frac{X}{p}$. The curve of $\frac{\alpha }{p}$ plotted as a function of $\frac{X}{p}$, for this case, shows a sharp peak at an $\frac{X}{p}$ of 350. This peak indicated the presence of some substance which is ionized by the excitation of hydrogen. The curves of $\frac{\beta }{\alpha }$ and $\gamma$ for the platinum cathode plotted as functions of $\frac{X}{p}$ show peaks at the lower values of $\frac{X}{p}$ which are analogous to those shown by Bowls. The curves for the NaH cathode show a narrow but remarkably high peak at an $\frac{X}{p}$ of 10. There are also several lower peaks but no general rise for the NaH cathode. These peaks indicate relatively large photoemission effects ($\frac{\Theta \eta g}{\alpha }$) at the cathodes at the lower values of $\frac{X}{p}$. In the case of the platinum cathode at the higher values of $\frac{X}{p}$ the curves show a general rise caused by electron emission due to the bombardment of the cathode by positive ions. The values of $\frac{\beta }{\alpha }$ and $\gamma$ for the sodium surfaces are much smaller than in the case of platinum for the higher values of $\frac{X}{p}$ 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 $\frac{X}{p}$. 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 $\gamma$-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.