A MOLECULAR-BEAM DETECTOR TO DETERMINE THE SPECIFIC OUTGASSING RATE OF SMALL SPECIMENS

A molecular beam detector was designed to measure the specific outgass ing rate of metal samples in the UHV region at reduced influence of th e gas desorbed from the walls of the chamber. The defector consists of a nude Bayard-Alpert gauge surrounded by a liquid nitrogen cooled sta inless steel tube. The orifice in direction to the sample was designed as a multicapillary system (MCS) containing 85 capillaries of 1 mm di ameter. Molecules desorbed from the sample can reach the interior of t he detector directional resolved by the MCS and can be detected. A shu tter between the MCS and the sample is used for the determination of t he background of the equipment. The derivation of the formulae for the determination of the specific outgassing rates from the pressure meas ured in the detector chamber is explained. First experimental results are discussed.