Laser Resonant Ionization Processes Of Lead Atom For The Measurement Of Lead Isotopes Ratio

The ratio of lead isotopes is widely used in exploring ocean resource, dating and tracing in marine environment, studying marine sediment, marine minerals and ore-forming material source, sorting the unknown mineral deposits and discriminating the tectonic background. Isotope dilution mass spectrometry (IDMS) and inductively coupled plasma mass spectrometry (ICPMS) are the two most usual methods for measuring the ratio of lead isotopes. But the two methods are complex for sample pre-preparation, long time-consuming and have serious isobaric interference. The newly developed method, laser resonance ionization spectroscopy (RIS) combined with laser ablation and mass analysis, can overcome these shortcomings and has show great potential in trace analysis. To make the most use of this method, some questions still have to be studied such as how to get saturated excitation and ionization for the chosen atoms, the optimization of laser intensity, how to lessen or eliminated the laser-induced isotopic discrimination effect of lead isotopes resulting from isotope shift and hyperfine structure of lead atom. These questions affect the veracity of the measurement of lead isotopes ratio greatly and the thesis focuses on these questions.This thesis includes three parts. In the first part, introduction and chapter 1, the applications of ratio of lead isotopes, the methods for the measurement of lead isotopes ratio, the theory, applications and development of laser resonance ionization spectrum are introduced. And the latest experimental and theoretical work is discussed.In the second part, chapter 2 and chapter 3, based on the population rate equations fordifferent RIS schemes, a calculating software is made which can calculate the particle number of energy levels under different multi-photon resonant ionization processes and the ionization efficiency with different laser intensity and irradiation time. With this software, the laser resonant ionization processes of lead isotope are numerically simulated. The rules of instantaneous particle number on some energy levels, ion number and ionization efficiency are investigated. The rules and threshold value of saturation excitation and ionization are achieved.In the third part, chapter 4 and chapter 5, the hyperfine structure of lead isotopes and isotope shift are introduced. And the laser-induced isotopic discrimination effect is studied. Some factors which may affect the probability of laser resonance transition such as the spectral line width of laser and atom, center wavelength of laser and resonance wavelength of atom are discussed. The dependences of laser-induced isotopic discrimination effect on the laser parameters, such as laser central wavelength, bandwidth and intensity are investigated. The method by which the laser-induced isotopic discrimination effect of lead isotopes is lessened or eliminated is given. Using wide band laser, wavelength optimization and high intensity laser is a better way.