This difference of conductivity in gases is due to unequal absorptions of the radiations. The writer has shown[1] that the total number of ions produced by the α rays for uranium, when completely absorbed by different gases, is not very different. The following results were obtained:
Gas Total
Ionization
Air 100
Hydrogen 95
Oxygen 106
Carbonic acid 96
Hydrochloric acid gas 102
Ammonia 101
The numbers, though only approximate in character, seem to show that the energy required to produce an ion is probably not very different for the various gases. Assuming that the energy required to produce an ion in different gases is about the same, it follows that the relative conductivities are proportional to the relative absorption of the radiations.
A similar result has been found by M^cLennan for cathode rays. He proved that the ionization was directly proportional to the absorption of the rays in the gas, thus showing that the same energy is required to produce an ion in all the gases examined.
46. Potential Gradient. The normal potential gradient
between two charged electrodes is always disturbed when the gas
is ionized in the space between them. If the gas is uniformly
ionized between two parallel plates, Child and Zeleny have shown
that there is a sudden drop of potential near the surface of both
plates, and that the electric field is sensibly uniform for the intermediate
space between them. The disturbance of the potential
gradient depends upon the difference of potential applied, and is
different at the surface of the two plates.
In most measurements of radio-activity the material is spread over one plate only. In such a case the ionization is to a large extent confined to the volume of the air close to the active plate. The potential gradient in such a case is shown in Fig. 9. The
- ↑ Rutherford, Phil. Mag. p. 137, Jan. 1899.
