Irradiation response of straw drift tubes

Drift tubes filled with Ar/CF//4/CO//2 (74:20:6) were exposed to 26 MeV proton beams from the Munich Tandem accelerator to study the radiation effects and operation characteristics expected for the COMPASS experiment at CERN. Stable operation with no significant loss of gain and no significant Malter current was observed up to charge accumulations of 1.1 C/cm. For comparison, with Ar/CH//4 (90:10) the same detectors show a 23% loss of gain and large Malter currents under the same irradiation condition. For Ar/CF//4/CO//2 a thin ( less than 0.1 mum) surface layer is observed by means of SEM on the anode wire in the irradiated detector section. As revealed by an ERDA study, the prominent components of this layer are C, O and Si.