Abstract

Experiences in vacuum testing of the 44″ cyclotron of Osaka University are discribed, which we have carried out since the end of last year.
In order to operate this cyclotron at the pressure of about 10^-3μHg, we had to detact so small leakage that was difficult to locate by usual leak location method and it was undesirable to use volatile liquids such as alcohol which filled up small leakage temporarily.
By the use of the massspectrometer using hydrogen gas we could detect leakage as small as 0.01 μl/min. easily.
Sensitivity proper to its leak detector decreased to about 1/51/10, owing to the fluctuation of the background of hydrogen peak.