Second Townsend Coefficient in Oxygen at High Pressures

The existence of the second Townsend ionization coefficient $\gamma$ in oxygen has been demonstrated in the presence of electron attachment. The experiment consisted of measurements of dc ionization currents in uniform electric fields at pressures near half an atmosphere and for electrode separations up to 3 cm. At a ratio of field strength to pressure of 35.4 volts (cm mm ${\mathrm{H}\mathrm{g})}^{-1\mathrm{}}$, $\gamma$ was found to be 0.045 for a nickel cathode. This is more than an order of magnitude larger than the values previously found for a nickel cathode in hydrogen and nitrogen. This large value of $\gamma$ compensates for the loss of electron multiplication due to negative-ion formation and results in comparable breakdown potentials for oxygen and nitrogen near atmospheric pressure.