Non-Metastable Penning Effect in the Alpha-Particle Ionization of Inert Gas Mixtures

An experimental investigation has been performed of the ionization yield by α particles in binary gas mixtures over the whole range of mixing ratio. The ionization yield for A-N 2 mixture, in which their ionization potentials are almost equal, agrees numerically well with the estimate from the theory proposed by Huber et al. on the assumption that the ionization yield in the individual component gas is proportional to the energy dissipated primarily by the α-particle in the gas. The additional ionization yield over the estimate from the theory is observed for He-Ne, A-Kr, A-Xe and Kr-Xe mixtures when the second gas is contained more than several percent in the mixture. This can be interpreted by the non-metastable Penning (NMP) ionization. For He-A mixture, the relative contribution of the NMP and metastable Penning (MP) process to the total ionization yield is estimated.