ATTAINMENT OF 10-9 mm Hg PRESSURE IN UNBAKED VACUUM SYSTEMS BY MOLYBDENUM EVAPORATION

摘要

The deposition of molybdenum by vaporization from simple hairpin fila¬ments has been found to reduce the pressure in an unbaked, stainless steel vacuum system to 4 x 10-10 mm Hg. The deposit of 300 milligrams from a single filament 0. 050 inch in diameter and about 6 inches long, has maintained an 85-liter volume at a pressure below 10-9 mm Hg for a period of over 40 hours. A small, well-trapped diffusion pump is attached to the system to attain the initial pressure of 10-7 mm Hg and to pump the ungettered com¬ponents which are presumably responsible for the ultimate pressure in the system. The geometrical area of the molybdenum substrate was 8 x 10³ cm². The initial pumping speed of this deposit was 4x104 liters per second for hydrogen.