Operation of an MHD converter requires an electrically conducting gas. It is proposed to use helium gas “seeded” with 1.0 mole percent cesium. The cesium is partly ionized (Cs Cs` e) by heating the mixture to 1800 K, 1 MPa, in a nuclear reactor to provide free electrons. No helium is ionized in this process, so that the mixture entering the converter consists of He, Cs, Cs`, and e. Determine the mole fraction of electrons in the mixture at 1800 K, where ln K 1.402 for the cesium ionization reaction described.