COMBINED NANO-COMPUTED TOMOGRAPHY AND X-RAY FLUORESCENCE EXPERIMENTS: A POWERFUL, NON-DESTRUCTIVE TECHNIQUE FOR THE IN-SITU CHEMICAL ANALYSES OF EXTRATERRESTRIAL MATERIALS

Correlated multi-technique analyses of individual stardust or presolar grains are the most effective way to constrain the stellar sources of the grains and gain information about their nucleosynthetic and chemical environments. Traditionally, destructive techniques like NanoSIMS and TEM of ultramicrotomed grain sections have been used to decipher the chemical, isotopic, and structural properties of stardust that provide an understanding of the circumstellar environments in which the grains condensed. TEM studies have provided major and minor elemental information on the nm-sized subgrains in presolar grains. However, TEM is, in principle, a non-destructive technique but requires the grains to be ultra-microtomed before analysis. This sample preparation procedure disrupts 3-d chemical information that could otherwise be recovered if the grains were studied intact. Stardust grains inherit their chemistry and subgrain population from the circumstellar gas, as they are blown through cooling outflows of dying stars. Observed radial trends in the chemical composition and subgrain size in individual grains reflect changes in gas chemistry and number density in the circumstellar region. Thus, it is vital to preserve the 3-d spatial structure of the grains during measurements.

This abstract presents a new technique that combines computed tomography (CT) and X-ray fluorescence (XRF) measurements at the nanoscale level to study presolar grains and their sub-grain populations. The technique will make constructing a 3-d chemical map of these grains straightforward. We present preliminary data that combines nano CT (nCT) and nano XRF (nXRF) measurements of one graphitic stardust grain to produce 3-d maps of the chemistry and microstructure of the grain. This method is called nano tomography-assisted chemical correlation (nTACCo). The data proves to be promising and demonstrates that nTACCo analysis can be a powerful technique to obtain nanoscale 3-d chemical and microstructural information on stardust grains and other cosmochemically relevant micro-particles. As nTACCo is a non-destructive technique, the material leftover from such an analysis is available for further correlated studies; thus, ascertaining efficient analysis of precious samples, such as those returned from a sample mission.