Early Irradiation of Matter in the Solar System: Magnesium (Proton, Neutron) Scheme

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Science  09 Jan 1976:
Vol. 191, Issue 4222, pp. 79-81
DOI: 10.1126/science.191.4222.79


The occurrence of positive and negative 26Mg anomalies in inclusions of the Allende meteorite is explained in terms of proton bombardment of a gas of solar composition. A significant fraction of 26Mg in the irradiated gas is stored temporarily in the form of radioactive 26Al by the reaction 26Mg(p,n) 26Al. Proton fluxes of 1017 to 1019 protons per square centimeter per year at l million electron volts are inferred. Aluminum-rich materials condensing from the gas phase have positive 26Mg anomalies, whereas magnesium-rich materials have negative 26Mg anomalies. The proton flux required to account for the observed magnesium anomalies is used to investigate possible isotopic anomalies in the elements from oxygen to argon. Detectable isotopic anomalies are predicted only for neon. The anomalous neon is virtually pure 22Ne from 22Na decay. The predicted amount of anomalous 22Ne is about 10–8 cubic centimeter (at standard temperature and pressure) per milligram of sodium.