DEGRADATION OF ALUMINUM DRIFT TUBES FILLED WITH AR-PERCENT-CO2+2.5-PERCENT-C4H10(15)

The degradation of aluminum drift tubes with gas at 3 atm and operatin g in both proportional and streamer modes has been studied. The degrad ation rate in the proportional mode is 25%/(C/cm). No significant vari ations in detector parameters were found in streamer mode at a low cou nt rate and a total accumulated charge of up to 14 C. At higher count rates, however, the ratio of the streamer to proportional signals chan ged as a result of degradation. The degradation rate in the streamer m ode can be determined from the maximum workload below which the detect or efficiency is constant plotted as a function of the accumulated cha rge.