Short-lived nuclides in hibonite grains from Murchison: evidence for solar system evolution

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 ¹⁰B that we attribute to the decay of short-lived ¹⁰Be (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--²⁶Al (half-life 700,000 years) and ⁴¹Ca (half-life 100,000 years)--that may be present in early solar system solids. One plausible source of the observed ¹⁰Be is energetic particle irradiation of material in the solar nebula. An effective irradiation dose of ~2 × 10¹⁸ protons per square centimeter with a kinetic energy of ≥10 megaelectronvolts per atomic mass unit can explain our measurements. The presence of ¹⁰Be, coupled with the absence of ⁴¹Ca and ²⁶Al, may rule out energetic particle irradiation as the primary source of ⁴¹Ca and ²⁶Al present in some early solar system solids and strengthens the case of a stellar source for ⁴¹Ca and ²⁶Al.