Measurement of breakdown potentials and Townsend ionization coefficients for the Penning mixtures of neon and xenon

The Townsend primary ($\alpha$) and secondary ($\gamma$) coefficients and Paschen curves for neon, xenon, and their mixtures are reported. The primary coefficient was determined by measuring the variation in the luminous flux in a self-sustained Townsend discharge between two parallel-plate nickel electrodes spaced 21.5 mm apart. The values of the reduced primary coefficient, $\frac{\alpha }{p_0}$, for Ne and Xe are about 10-20% lower than published values obtained by the classical method of Townsend. The $\frac{\alpha }{p_0}$ values obtained for Ne agree with previous work using the same luminous-flux method. The ionization efficiency function $\eta$ $\eta =\frac{\alpha }{E}$, where $E$ is the electric field) has a maximum value for Ne and 0.01% Xe. Also, the value of $\eta$ for this gas mixture is larger than that for Ne + 0.1% Ar, especially at small values of $\frac{E}{p_0}$ (1-10 V ${\mathrm{cm}}^{-1\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$).