Resonance ionization mass spectrometry at Los Alamos National Laboratory

Two approaches to RIMS will be discussed here. The first is the use of continuous-wave (cw) dye lasers as the ionization source. Continuous excitation effectively matches the ionization to the evaporation of sample from a resistively heated filament, providing for efficient use of the sample. In addition, cw ionization permits pulse counting detection, necessary for the measurement of large isotope ratios on small samples. In the cases of lutetium and technetium discussed below, average ionization rates with cw ionization are much larger than with pulsed ionization. The second approach to RIMS is the use of multiphoton resonances in the pulsed laser excitation of atoms. The potential advantages derived from the use of n-photon resonances (n greater than or equal to 2) include minimal laser hardware, since the fundamental output of a single dye laser is sufficient to effect ionization in a large number of elements. The possibility also exists for Doppler-free excitation, which could be used to increase the selectivity of the ionization process. Experiments with 2 + 1 (photons to resonance plus photons to ionize) RIMS schemes for several elements will be discussed. 5 refs., 2 figs., 1 tab