Shinku

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In a vacuum apparatus outgassing rate can be calculated from the pressure variation after the valve is closed. This process is called the build-up-test. The build-up-test for the apparatus constructed with stainless steel (trap, valve and piping), copper (mass spectrometer casing) and Teflon gasket has been studied using an ionization gauge, a Pirani gauge and a gas detector (180° type mass spectrometer).
A main constituent is N₂+CO component, M/e=28, in the gases evolved during the test. The pressure variation for each component is markedly influenced by the pumping action of the ionization gauge.
The ratio, pa/po, between the final pressure observed and that calculated from the build-up-test is also discussed. pa/po for M/e=2, 12, 14, 16 and 28 are situated at the value 15. It is 20500 for M/e=18, 40, 44 and others larger than 50. pa/po for the total pressure is 611. It is clarified that pa/po for the total pressure is increased with amounts of components of M/e=18, 40, 44 and others larger than 50.
A slow rate desorption is observed in the build-up-test done for 200 hrs. The saturation pressure and the activation energy of desorption for this case are 10^-2 Tom and 24 Kcal/mole, respectively.
Water vapour is a main component of residual gases in the apparatus evacuated for 15hrs. at the room temperature without liquid oxygen trap. The partial pressure of water vapour can be, however, much reduced by the evacuation for 15hrs. at 150°C bakeout with liquid oxygen trap.

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