PERMEATION OF ARGON, CARBON-DIOXIDE, HELIUM, NITROGEN, AND OXYGEN THROUGH MYLAR WINDOWS

In secondary beam lines in the alternating gradient synchrotron (AGS) at Brookhaven National Laboratory, low mass vacuum windows are used to reduce background radiation near particle detectors. These windows ar e fabricated using Mylar (a registered trademark of Dupont) films and are generally made as thin as possible. Mylar films as thin as 0.002 i n. have been used as vacuum windows ranging in size up to 36 in. X76 i n. When using Mylar for low mass window applications, permeation must be considered to achieve system design pressures. The permeation of se veral different gas species through both Mylar and aluminized Mylar fi lms with thicknesses of 0.002 in. and 0.005 in. has been studied. Test ing was performed under high vacuum and a quadrupole mass spectrometer was used to identify and quantify gas species during the study. The p ermeability of argon, carbon dioxide, helium, nitrogen, and oxygen wer e determined for Mylar from 20-degrees-C up to 90-degrees-C.