脉冲激光蒸发共振电离飞行时间质谱法测定铅和铋同位素

Pulsed Laser Evaporation for Detection of Lead and Bismuth with Resonance Ionization Time-of-flight Mass Spectrometry

本文采用532nm脉冲激光蒸发作为共振电离飞行时间质谱测定铅和铋和样品原子化源.在5×10~7W/cm^2激光功率密度条件下,样品原子化过程为--非热平衡蒸发过程,由此产生的原子束的最可几速率可达700m/s.和连续热原子化源相比,样品的利用率提高了约三个量级.采用1+1共振电离飞行时间质谱测定了铅和铋,结果表明本实验系统可以测定同位素比为100:l的元素,并显示出很好的选择性.

A pulsed Nd:YAG laser (532nm) was used to vaporize lead and bismuth atoms from metal samples at room temperature. These atoms were subsequently detected by pulsed resonance photoioniza-tion and time-of-flight mass spectrometry. By varying the time delay between the vaporization laser and the ionization laser, arrival time distributions of atoms were obtained. Ground state bismuth atoms were found to have a most probable hydrodynamic velocity of 700m/s for vaporization pulse intensities of 5×107W/cm2, overlap of the atom pulse and the ionization laser pulse was good, with more than 1% effective duty cycle. A one color two-photon (1 + 1) ionization scheme was employed utilizing UV light at 283. 39nm and 306. 89nm provided by a Nd: YAG pumped dye laser with frequency doubling for Pb and Bi atoms, respectively. Our results show that no interference from the other elements or impurities were detected, and all isotopic abundances were in good agreement with published values, in the case of Pb. It is suggested that the capability for lead isotopic ratio measurements is in excess of 100:1 with suitable experimental conditions.