Generation of SQS in quenching gas (CH4) of proportional counter and related problems

Two topics concerning the self-quenching streamer (SQS) phenomenon in proportional counters are reported. One is the observation of the SQS transition in pure methane gas under irradiation with 4.5-kV X-rays. The effect of a small amount of argon on the SQS transition was investigated with gas mixtures (CH/sub 4/ 4:Ar) having mixing ratios of 100:0, 99.8:0.2, 99.7.03, 99.5:0.5, 99:1, 98:2, 95.5:0.5, and 90:10. A SQS transition was not observed in pure methane gas, although it was observed in the gas mixture of 99.8:0.2. The other topic discussed is the measurement of electron drift characteristics with a single-wire gas counter operated in the SQS transition regions. The counter gas used was a mixture of argon and methane (70:30) to which ethanol vapor was added. From comparison with the proportional mode, the use of the SQS mode is recommended to obtain a better time resolution in the application of the drift counter.<>