ON AN IRRADIATION ORIGIN FOR MAGNESIUM ISOTOPE ANOMALIES IN METEORITIC HIBONITE
We investigate spallogenic effects on magnesium isotopic compositions in solids with hibonite-like (CaAl{sub 12}O{sub 19}) chemistry under an irradiation setting in the early solar system. We consider a series of nuclear reactions triggered by gradual flare irradiation, with an energy spectrum dN/dE {proportional_to} E {sup -2.7} and a proton flux F{sub p} (E{>=} 10 MeV) = 1.9 x 10{sup 10} cm{sup -2} s{sup -1}, on isotopically normal hibonite-like solids. The proton fluence is constrained by matching the {sup 10}Be/{sup 9}Be measured in meteoritic hibonite platy crystals. The net result, accounting for both production and destruction reactions of Mg isotopes, shows small deviations from the terrestrial isotopic composition with the sign and magnitude of {delta}{sup 26}Mg effects dependent on both low energy cutoff and total fluence. The total span of predicted spallogenic deviations can explain small apparent {sup 26}Mg excesses observed in some hibonite grains, but does not account for the magnitude of apparent {sup 26}Mg deficits found in other grains. As previously indicated, irradiation by gradual flares decouples {delta}{sup 26}Mg variations and {sup 26}Al/{sup 27}Al from {sup 10}Be/{sup 9}Be.
- OSTI ID:
- 21307968
- Journal Information:
- Astrophysical Journal (Online), Vol. 697, Issue 2; Other Information: DOI: 10.1088/0004-637X/697/2/L145; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-4357
- Country of Publication:
- United States
- Language:
- English
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