The elusive (60)Fe in the solar nebula

No (60)Ni or (61)Ni anomalies have been detected in troilite inclusions from Muonionalusta, a 4565.3 +/- 0.1 Ma old IVA iron meteorite, to the level of the analytical precision of 10 ppm. Because Muonionalusta troilite is very old, has a high Fe/Ni ratio, and is free of (61)Ni anomalies, it is the ideal material in which to search for potential excesses of (60)Ni produced by the decay of (60)Fe (t(1/2) = 2.62 Ma). The (60)Ni/(58)Ni and Fe/Ni ratios (up to 1680) measured here imply an upper limit for the initial (60)Fe/(56)Fe for the Muonionalusta troilite of 3 x 10(-9). Assuming that (60)Fe was homogeneously distributed across the nebula, this result suggests that the solar system initial (60)Fe/(56)Fe ratio was less than 5 x 10(-9), which is lower than previously measured by at least a factor of 50