Shinku

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Interaction of hydrogen with a Bayard-Alpert type ionization gauge has been studied in order to know the possibility of the measurement of hydrogen pressure by an ionization gauge. The gauge has a grid made of platinum clad molybdenum wire, a thoria coated tungsten filament and a pure tungsten filament. The pumping speed of the gauge using thoria coated filament or using tungsten filament has been measured successively, as a function of filament current or filament temperature. The results show that the pumping speed is consisted of at least two parts. One of them is the pumping action due to the reaction of hydrogen with hot filament and the other one is the pumping action caused by the electron current. The latter pumping action includes very complex phenomena which are not clarified in this report.
As the results of the measurements of pumping speed and the mass spectrometric observations of impurity production, following conditions are recommended for the pressure measurement of hydrogen : (1) Thoria coated filament should be used at the temperature lower than 1440°K. This means that the filament must be well activated. (2) The electron current should be sent as short duration as possible in order to avoid the production of impurities which will hinder the electron emission of thoria coated filament.

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