Short-Lived Nuclides in Hibonite Grains from Murchison: Evidence for Solar System Evolution

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Abstract
Records of now-extinct short-lived nuclides in meteorites provide information about the formation and evolution of the solar system. We have found excess 10 B that we attribute to the decay of short-lived 10 Be (half-life 1.5 million years) in hibonite grains from the Murchison meteorite. The grains show no evidence of decay of two other short-lived nuclides— 26 Al (half-life 700,000 years) and 41 Ca (half-life 100,000 years)—that may be present in early solar system solids. One plausible source of the observed 10 Be is energetic particle irradiation of material in the solar nebula. An effective irradiation dose of ∼2 × 10 18 protons per square centimeter with a kinetic energy of ≥10 megaelectronvolts per atomic mass unit can explain our measurements. The presence of 10 Be, coupled with the absence of 41 Ca and 26 Al, may rule out energetic particle irradiation as the primary source of 41 Ca and 26 Al present in some early solar system solids and strengthens the case of a stellar source for 41 Ca and 26 Al.