Characterization of contaminant outgassing from the detection module Mylar assembly used in the proton decay experiment

Excessive amount of methylene chloride, the solvent of the glue used in preparing the parts for the proton decay detection modules, has been identified as the contaminant that jeopardized the detecting capability of the ten newly built detection modules. The poisoned Mylar sheets have been found to produce ten times the amount of outgassed air and chlorine related species than the normal Mylar sheets. Under 50°C, chlorine related species accounted for about 25% of the total outgassed species. The above findings are based on the measurements and diagnosis of a newly developed mass spectrometer molecular beam system with ppb range trace constituent detection capability.