| Popis: |
Ionization in various gases by electrons of energy 0-325 volts.---Electrons from a hot filament were projected through an ionization chamber $B$ containing gas at low pressure (.001 to.005 mm) and into a trap. Positive ions produced in $B$ were collected on fine wires arranged in the form of a squirrel cage $C$ and maintained at a potential lower than $B$ by an amount ${V}_{r}$. Corrections were made for the facts (1) that the wires $C$ lowered the potential at the center of $B$ and hence retarded the electrons passing through $B$ by a maximum amount of $0.4\ifmmode\times\else\texttimes\fi{}{V}_{r}$, and (2) that if ${V}_{r}$ was numerically less in value than the accelerating potential ${V}_{\ensuremath{\alpha}}$, some primary electrons reached $C$. The pressures were measured with a McLeod gauge to 1 percent and were corrected for the heating effect of the filament, which was determined by using the apparatus as an ionization manometer to be about 26\ifmmode^\circ\else\textdegree\fi{}. The resulting curves for $N$, the number of ions per cm path produced by an electron moving through a gas at 1 mm pressure, are believed correct within a few percent. In agreement with previous results of Hughes and Klein and others, the curves each rise to a maximum. The maximum values found and the corresponding voltages are as follows: The values for $P(max)$, the corresponding probability that a collision will result in ionization of the hit molecule, were computed from $N(max)$ assuming the kinetic theory values for electronic mean free paths. These results are compared with previous experimental values. Ionization was found to begin at the ionizing potential in each case, except that with ${\mathrm{N}}_{2}$ weak ionization was observed at 10 volts. This may possibly be associated with the presence of traces of active nitrogen. |
