Erdmann Nicole, Betti Maria, Kollmer Felix, Benninghoven Alfred, Grüning Carsten, Philipsen Vicky, Lievens Peter, Silverans Roger E, Vandeweert Erno
Institute for Environment and Sustainability, European Commission Joint Research Center, T.P. 290, I-21020 Ispra (VA), Italy.
Anal Chem. 2003 Jul 1;75(13):3175-81. doi: 10.1021/ac0264426.
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.
分别研究了从薄金属膜和单个微米级氧化铀颗粒溅射出来的铀原子的共振和非共振激光电离，以评估一种用于分析含锕系元素的微米级颗粒的新装置。使用非共振（193纳米）电离微米级氧化铀颗粒溅射出来的原子和分子的实验表明，溅射中性原子的铀检测效率比二次离子高约2个数量级。在直径为0.5微米的铀颗粒中，很容易检测到6×10⁶个²³⁵U原子，²³⁵U/²³⁸U = 0.0048±4.6%的同位素比与认证值非常吻合。研究了对从薄膜溅射出来的中性铀原子进行双色、两步共振电离的方法。测试了几种激发方案，并观察到离子溅射后几个低激发亚稳态的显著粒子数。确定了双共振电离的自电离态，并通过比较共振和非共振多光子（355纳米）激光后电离获得的不同溅射物种的飞行时间分布，说明了涉及这些自电离态的电离方案的高选择性。理想情况下，共振和非共振电离的选项将在单个装置中结合起来，以大幅提高灵敏度和选择性。因此，可以从同一个单颗粒中获得有关微量元素主要成分以及特定同位素信息。
