| Abstract
| - The resonance and nonresonant laser ionization of uranium atoms sputtered from thin metal films and individual micrometer-size uranium oxide particles, respectively, was studied to evaluate a new setup for the analysisof actinide-containing micrometer-size particles. Experiments using nonresonant (193-nm) ionization of atomsand molecules sputtered from micrometer-size uraniumoxide particles have shown that the uranium detectionefficiencies for sputtered neutral atoms are ∼2 orders ofmagnitude higher than for secondary ions. In uraniumparticles of 0.5-μm diameter, 6 × 106 atoms of 235U wereeasily detected and the isotopic ratio of 235U/238U =0.0048 ± 4.6% is in excellent agreement with the certifiedvalue. The use of two-color, two-step resonance ionizationof the sputtered neutral uranium atoms from thin filmswas investigated. Several excitation schemes were tested,and a significant population of several low-lying metastablestates after ion sputtering was observed. Autoionizingstates for double-resonant ionization were determined,and the high selectivity of ionization schemes involvingthese autoionizing states was illustrated by comparing theflight-time distributions of different sputtered speciesobtained both by resonance and nonresonant multiphoton(355-nm) laser postionization. Ideally, the options forresonance as well as nonresonant ionization would becombined in a single setup, to obtain a large gain insensitivity and selectivity. Thus, information about themain components as well as specific isotopic informationof a trace element could be obtained from the same singleparticle.
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