Chromium Fluence Measurements in Genesis Samples Using A Nanosims

Our Sun holds most of the mass of the solar system (99.9%) and its chemical and isotopic composition thus provides the reference standard for astronomical, cosmochemical and geochemical studies. The Genesis mission returned solar wind implanted samples for studying solar wind composition. Previous studies of solar wind Cr fluence in Genesis samples showed over-estimates of it due to surface contamination [1–2]. We analyzed three different Si target samples (60040, 30877 and 60490) by NanoSIMS. With smaller analysis area (10–15 µm^2 in a 30 µm^2 rastered area) and meticulous cleaning procedures (sample 60490) [3], the surface contamination of Cr can be avoided. We obtained an average Cr fluence value 3.3 ± 1.1 × 10^(10)atom/cm^2 (2σ).