抄録
When a cold system installed to a vacuum apparatus is cooled to obtain an ultra high or extreme high vacuum state, one often faces the problem of “cold leak”. In this paper we report the first quantitative measurement of “cold leak” of liquid nitrogen through aluminium welding faults whose leak rate of room temperature helium gas is 10-21 lusec. At 1 atm the leak rate of liquid nitrogen is about 8 times larger than that of nitrogen gas of room temperature at 1 atm, and when the pressure of liquid nitrogen is increased to 2 atm and 3 atm the leak rate becomes about 40 and 100 times respectively. This remarkable pressure dependance of liquid nitrogen leak rate is studied from a simple theory.
