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A spectroscopic investigation of the ionisation of argon by electron collisions

1922; Royal Society; Volume: 102; Issue: 715 Linguagem: Inglês

10.1098/rspa.1922.0076

2053-9150

Frank Horton, Ann Catherine Davies,

Electrohydrodynamics and Fluid Dynamics

The authors have previously described an investigation of the effects of electron collisions with argon atoms,* in which the production of radiation and of ionisation was looked for, using a delicate electrometer as the detecting instrument. As the result of these experiments, it was found that the value of the minimum electron energy for the production of resonance radiation from argon was 11·5 volts, and the minimum electron energy necessary for the detachment of a single electron from a normal argon atom was 15·1 volts. Since the publication of these results some other investigations of the critical voltages for electrons in argon have been published. Several of these were made using argon as a gas filling for a thermionic valve, but the precise methods of arranging the electric fields, and of carrying out the experiment differed somewhat in different cases. The values of the ionisation voltage deduced by the various observers are not in good agreement. For instance, from experiments with three-electrode valves, Stead and Gossling concluded that this value is 12·5 volts, Hodgson and Palmer that it is 16·6 volts, and Déjardin* that it is 15·0 volts. Found, using a two-electrode tube, obtained the value 15·6 volts, whereas Rentschler, using a three-electrode apparatus, had previously given 17 volts as the ionisation voltage. In attempting to account for these discordant values it may be mentioned that in the authors’ experiments, already referred to, a very marked discontinuous increase of current occurred a few volts higher than the stage at which ionisation was first detected. This increase of current took place at a potential difference which varied over a range of several volts, but which was never below the ionisation voltage. At certain pressures it was accompanied by the appearance of luminosity in the gas. The effect was attributed to the largely increased electron emission from the glowing filament when neutralisation of the space charge of the electrons in its neighbourhood occurred. It seems not improbable that the effect obtained by Rentschler at 17 volts, and interpreted by him as the beginning of ionisation, in reality indicates the stage when neutralisation of the space charge of the emitted electrons takes place. It also seems probable that the very low value (12·5 volts) obtained by Stead and Gossling must have been due to the presence in the apparatus of some impurity which was ionisable by the argon radiation.