THE TRANSITION FROM PROPORTIONAL TO STREAMER MODE IN A RESISTIVE PLATE CHAMBER

We show that proportional pulses as well as streamer pulses can be detected in an RPC over a range of voltages below the onset of full streamer efficiency. The transition is similar to that seen in limited streamer tubes with thick wires. The streamer pulses are preceded in time by a proportional pulse i.e. there is a prepulse. The timing resolutions of these different types of pulses are measured as a function of high voltage and for various gas mixtures of argon, isobutane and freon. The possibility of using a large proportion of freon in order to reduce the streamer charge and improve the rate capability of the RPC is discussed.