The application of neon flash tubes to studies of cosmic rays

Abstract

A study has been made of the characteristics of neon flash tubes with a view to their use in cosmic ray work, and for machine experiments. In particular their low efficiency when operated at high repetition rates has been investigated, and this is thought to be due to fields set up by charge deposited on the glass as a result of the discharge. The fields are shown to decay with a time constant consistent with conduction of electrons over the glass surface to neutralise positive ions deposited on the other side of the tube. A long term effect has also been encountered, and is thought to be due to fields caused by electrons trapped in the glass. The discharge laechanism has been examined and shown to be, in most cases, a combination of streamer and Townsend breakdown. The most probable method of propagation down the tube is that several discharges are initiated along the tube by photoemission from the walls caused by photons from the initial and successive avalanches. When the field due to charge separation effectively backs off the applied field, the discharge is quenched. A random walk method has been developed to solve the equation of diffusion and drift for electrons in a flash tube, taking formative distance into account, and hence the fields built up during the experiment have been estimated, and compared with values calculated from the decay constant obtained from the resistivity of the glass and the capacitance of the tube. Some methods of overcoming the clearing field effect, namely increased surface conductivity, and the use of a bipolar ringing pulse, have been successfully tried, with a view to making the efficiency of flash tubes independent of repetition. rate.