The first ionization potential of uranium and thorium measured in a d.c. arc plasma

Tha Saha relationship was used to derive the ionization potentials of uranium and thorium from measurements of temperature or of electron density in a plasma in thermodynamic equilibrium. Introducing into the plasma elements with well defined ionization potentials, such as Ba, Al, V, Cr, Zr, Mo, Cu, Si and some of the rare-earths, as matrices, the temperature and electron density were measured in the central region of the arc plasma. A relation was established between the different ionization potentials and the plasma temperature or the electron density. From this relation the values of 6.3 ± 0.3 and 7.5 ± 0.3 eV were found for the ionization potentials of U and Th respectively.