Quantification of Surface Contamination on Genesis Solar Wind Samples

The Genesis mission was the only mission returning pristine solar material to Earth since the Apollo program up to date [1, 2]. Unfortunately, the return of the spacecraft on September 8, 2004 resulted in a crash landing shattering the solar wind collectors into small fragments and exposing them to desert soil and other debris at the landing site. To permit analysis of solar wind material embedded within a collector, surface cleaning is a necessity. Cleaning should remove surface contamination quantitatively, but leave the embedded solar wind intact. However, contamination varies from sample to sample and each fragment requires an individual cleaning approach. To ensure that cleaning is effective a sample has to be inspected carefully before and after cleaning was performed. This is done optically using a microscope and also spectroscopically by using total reflection X-ray fluorescence (TXRF) analysis. Total reflection X-ray fluorescence is a nondestructive surface sensitive multi element analysis method and has been applied to a number of Genesis solar wind samples before and after various cleaning methods. [3-5]. In case contaminants remain after cleaning, quantification of those is important to evaluate the effectiveness of the procedure itself and to provide information about a sample for other investigators. Quantification is typically done by addition of an internal standard for TXRF analysis, but this approach is not possible for Genesis samples as it would introduce additional contamination. In this study, external calibration curves were produced instead and the concentration of remaining elements determined for three flight samples after different cleaning procedures were applied.