Trace isotopic analysis of micron-sized grains: Mo and Zr analysis of stardust (SiC and graphite grains)

摘要

Abstract: Secondary Neutral Mass Spectrometry using resonant laser ionization can provide for both high useful yields and high discrimination while maintaining high lateral and depth resolutions. An example of the power of the method is measurement of the isotropic composition of Mo and Zr in 1-5 $mu@m presolar SiC and graphite grains isolated form the Murchison CM2 meteorite for the first time. These grains have survived the formation of the Solar System, and isotopic analysis reveals a record of the stellar nucleosynthetic processes known as s-, p-, and r-process. Successful isotopic analysis of these elements requires both high selectivity and high efficiency. Resonant ionization spectroscopy is particularly useful and flexible in this application. While the sensitivity of this technique has often been reported in the past, we focus here on the very low noise properties of the technique. We further demonstrate the efficacy of noise removal by two complimentary methods. First we use the resonant nature of the signal to subtract background signal. Second we demonstrate that by choosing the appropriate resonance scheme background can often be dramatically reduced. !20