SELECTIVE RESONANT IONIZATION OF ZIRCONIUM ISOTOPES USING INTERMEDIATE-STATE ALIGNMENT

High selectivity (> 10) for separation of Zr-91 from other Zr isotopes was observed during triple resonant ionization of Zr. vapors. Linearl y polarized lasers were used to prepare aligned states, from which fur ther excitation to a discovered J = 0 level could be suppressed for ev en-mass isotopes, by a suitable choice of relative laser polarization. Photoionization of the odd-mass isotope Zr-91 could be retained by us e of transitions with relatively strong hyperfine interactions, becaus e of associated population redistributions in the magnetic sublevels. The dependence of the even-mass-isotope signals on relative laser pola rization followed sinusoidal forms, which axe in excellent agreement w ith predictions derived from the geometric components of the transitio n dipole moment. The isotopic selectivity for Zr-91 can be increased b y use of saturating fluences, because of the effects of saturation, po pulation trapping in the even-mass isotopes, and strong hyperfine inte ractions in the odd-mass isotopes. For the same reasons, biases in eve n:odd isotope ratio measurements cannot always be eliminated by polari zation scrambling or special angles.