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Iron-60 (t1/2=2.62 Myr) is a short-lived nuclide that can help constrain theastrophysical context of solar system formation and date early solar systemevents. A high abundance of 60Fe (60Fe/56Fe= 4x10-7) was reported by in situtechniques in some chondrules from the LL3.00 Semarkona meteorite, which wastaken as evidence that a supernova exploded in the vicinity of the birthplaceof the Sun. However, our previous MC-ICPMS measurements of a wide range ofmeteoritic materials, including chondrules, showed that 60Fe was present in theearly solar system at a much lower level (60Fe/56Fe=10-8). The reason for thediscrepancy is unknown but only two Semarkona chondrules were measured byMC-ICPMS and these had Fe/Ni ratios below ~2x chondritic. Here, we show thatthe initial 60Fe/56Fe ratio in Semarkona chondrules with Fe/Ni ratios up to~24x chondritic is 5.4x10-9. We also establish the initial 60Fe/56Fe ratio atthe time of crystallization of the Sahara 99555 angrite, a chronologicalanchor, to be 1.97x10-9. These results demonstrate that the initial abundanceof 60Fe at solar system birth was low, corresponding to an initial 60Fe/56Feratio of 1.01x10-8.

Low 60Fe abundance in Semarkona and Sahara 99555