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

Abstract

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.