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Such so-called seed electrons can be created by ionization by natural radioactivity or cosmic rays. The creation of further free electrons is only achieved by impact ionization. Thus Paschen's law is not valid if there are external electron sources. This can, for example, be a light source creating secondary electrons by the photoelectric ...
Townsend's early experimental apparatus consisted of planar parallel plates forming two sides of a chamber filled with a gas.A direct-current high-voltage source was connected between the plates, the lower-voltage plate being the cathode and the upper-voltage the anode.
Paschen-Back effect, the splitting of atomic energy levels in the presence of a strong magnetic field Paschen series, a Hydrogen spectral series in the infrared band Paschen's law , an equation that gives the breakdown voltage, that is the voltage necessary to start a discharge or electric arc, between two electrodes in a gas as a function of ...
The relationship between this breakdown voltage and the pd product—where p is the gas pressure and d is the distance between the electrodes—is referred to as Paschen's law. [1] [2] For a range of gas molecules, the breakdown voltage estimated by Paschen's law has a minimum value of around pd = 1-10 Torr cm. This suggests that in order to ...
At low voltages, the only current is that due to the generation of charge carriers in the gas by cosmic rays or other sources of ionizing radiation. As the applied voltage is increased, the free electrons carrying the current gain enough energy to cause further ionization, causing an electron avalanche. In this regime, the current increases ...
The ionization with its characteristics (see above) is not influenced by the coupling, allowing the same ionization method to be used for different chromatography couplings. The ability to couple gas chromatography with a low-fragmentation ionization technique on an LC-MS, for example, can be utilized in the analysis of saturated hydrocarbons .
As the electric field is increased various phases of discharge are encountered as shown in the accompanying plot. The gas used dramatically influences the parameters of the tube. The breakdown voltage depends on the gas composition and electrode distance; the dependencies are described by Paschen's law.
Adiabatic ionization is a form of ionization in which an electron is removed from or added to an atom or molecule in its lowest energy state to form an ion in its lowest energy state. [14] The Townsend discharge is a good example of the creation of positive ions and free electrons due to ion impact.