LOW 60FE ABUNDANCE IN SEMARKONA AND SAHARA 99555

Iron-60 (t(1/2) = 2.62 Myr) is a short-lived nuclide that can help constrain the astrophysical context of Solar System formation and date early Solar System events. A high abundance of Fe-60(Fe-60/Fe-56 approximate to 4 x 10(-7)) was reported by in situ techniques in some chondrules from the LL3.00 Semarkona meteorite, which was taken as evidence that a supernova exploded in the vicinity of the birthplace of the Sun. However, our previous multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements of a wide range of meteoritic materials, including chondrules, showed that Fe-60 was present in the early Solar System at a much lower level (Fe-60/Fe-56 approximate to 10(-8)). The reason for the discrepancy is unknown but only two Semarkona chondrules were measured by MC-ICPMS and these had Fe/Ni ratios below similar to 2x chondritic. Here, we show that the initial Fe-60/Fe-56 ratio in Semarkona chondrules with Fe/Ni ratios up to similar to 24x chondritic is (5.39 +/- 3.27) x 10(-9). We also establish the initial Fe-60/Fe-56 ratio at the time of crystallization of the Sahara 99555 angrite, a chronological anchor, to be (1.97 +/- 0.77) x 10(-9). These results demonstrate that the initial abundance of Fe-60 at Solar System birth was low, corresponding to an initial Fe-60/Fe-56 ratio of (1.01 +/- 0.27) x 10(-8).