title: Resonance and nonresonant laser ionization of sputtered uranium atoms from thin films and single microparticles: evaluation of a combined system for particle trace analysis.
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 analysis of actinide-containing micrometer-size particles. Experiments using nonresonant (193-nm) ionization of atoms and molecules sputtered from micrometer-size uranium oxide particles have shown that the uranium detection efficiencies for sputtered neutral atoms are approximately 2 orders of magnitude higher than for secondary ions. In uranium particles of 0.5-microm diameter, 6 x 10(6) atoms of 235U were easily detected and the isotopic ratio of 235U/238U = 0.0048 +/- 4.6% is in excellent agreement with the certified value. The use of two-color, two-step resonance ionization of the sputtered neutral uranium atoms from thin films was investigated. Several excitation schemes were tested, and a significant population of several low-lying metastable states after ion sputtering was observed. Autoionizing states for double-resonant ionization were determined, and the high selectivity of ionization schemes involving these autoionizing states was illustrated by comparing the flight-time distributions of different sputtered species obtained both by resonance and nonresonant multiphoton (355-nm) laser postionization. Ideally, the options for resonance as well as nonresonant ionization would be combined in a single setup, to obtain a large gain in sensitivity and selectivity. Thus, information about the main components as well as specific isotopic information of a trace element could be obtained from the same single particle.
authors.affiliation: Institute for Environment and Sustainability, European Commission Joint Research Center, T.P. 290, I-21020 Ispra (VA), Italy. nicole.erdmann@jrc.it
authors.forename: Nicole
authors.initials: N
authors.lastname: Erdmann
authors.forename: Maria
authors.initials: M
authors.lastname: Betti
authors.forename: Felix
authors.initials: F
authors.lastname: Kollmer
authors.forename: Alfred
authors.initials: A
authors.lastname: Benninghoven
authors.forename: Carsten
authors.initials: C
authors.lastname: Grüning
authors.forename: Vicky
authors.initials: V
authors.lastname: Philipsen
authors.forename: Peter
authors.initials: P
authors.lastname: Lievens
authors.forename: Roger E
authors.initials: RE
authors.lastname: Silverans
authors.forename: Erno
authors.initials: E
authors.lastname: Vandeweert