Investigation of Electron Avalanches in Air using a Cloud Chamber

ABSTRACT The growth of electron avalanches has been studied in a homogenous field electrode configuration in air using an expansion cloud chamber. The effect of such parameters as the expansion ratio, type of vapour and irradiation of the cathode on the avalanche growth has been studied. The velocity of the avalanche growth was measured in air at pressures of 400, 580 and 680 mm of Hg for values of X/p from 30 to 40 volts/cm/mm. The measurements of Raethor at X/p of 41 volts/cm/mm (pressure 270 mm of Hg) tend to agree with the present experimental values extrapolated. Both the results of Nielsen and Bradbury and Townsend and Tizard appear to be higher by about 12%. Estimates have been made of the thermal energy of the electrons from both the avalanche width and velocity and large discrepancies have been found.