Study of a self quenching streamer mode in pure gases of DME and isobutane

A self quenching streamer (SQS), or limited streamer mode has been studied in single wire chambers with cross-sections 12x12 mm and wire diameters 15, 25 and 50 microns. Chambers were filled with either pure dimethyl ether (DME) or isobutane gases and irradiated with Gd-148 alpha and Fe-55 x-ray sources. Clear transitions from a proportional to 100% SQS mode were observed on all three diameter wires with both gases irradiated with alpha particles. Double SQS discharges due to inclined tracks observed in DME gas allowed an estimation of a streamer size along the wire of less than 1 mm. The second SQS discharge appears less than 1 mm from the first within about 500 ns. Charge spectra obtained with DME irradiated with Fe-55 x-rays might also be interpreted as a transition to a SQS mode, although no direct evidence of that was seen in the observed pulse shapes.