Abstract: Isotope separation method and means are shown wherein an atomic beam containing two or more isotopes is exposed to radiation at a predetermined first wavelength to excite atoms of only one said isotope to a first intermediate excited state without substantially exciting atoms of other isotopes. These excited atoms are excited by a second radiation source at a second predetermined wavelength to a state of high principal quantum number, a Rydberg state, beneath the ionization continuum, again substantially without exciting atoms of said other isotopes to such high energy levels since substantially none of the other isotopes are in the intermediate excited state. From this bound atomic level only slightly below the ionization limit, the highly excited atoms are field ionized by electron tunneling and thence removed from the nonionized atoms by use of a moderate electric field.