TY - JOUR
T1 - γ-ray irradiation in the early Solar System and the conundrum of the 176Lu decay constant
AU - Albarède, Francis
AU - Scherer, Erik E.
AU - Blichert-Toft, Janne
AU - Rosing, Minik
AU - Simionovici, Alexandre
AU - Bizzarro, Martin
PY - 2006
Y1 - 2006
N2 - When recent geological calibrations of the 176Lu decay constant are used, the 176Lu-176Hf ages of chondrites are consistently 4% too old (∼4.75 Ga). Here, we suggest that this discrepancy reflects the photoexcitation of the long-lived 176Lu ground state to the short-lived isomeric state (T1/2 = 3.7 h) by γ-rays irradiating early condensates. Irradiation may have been of solar origin and taking place at the inner edge of the nebular disk. Alternatively, the source of γ-rays could have been one or more supernova(e) exploding in the vicinity of the solar nebula. Such photoexcitation has been experimentally observed, but requires γ-ray photons that have energies in excess of 838 keV. At this stage, we cannot assess whether the Hf isotope composition of the Bulk Silicate Earth differs from that of chondrites, eucrites, and the 4.56 Ga old Martian meteorite ALH84001, and therefore, whether the precursor material for these different planetary bodies received comparable fluences of γ-rays.
AB - When recent geological calibrations of the 176Lu decay constant are used, the 176Lu-176Hf ages of chondrites are consistently 4% too old (∼4.75 Ga). Here, we suggest that this discrepancy reflects the photoexcitation of the long-lived 176Lu ground state to the short-lived isomeric state (T1/2 = 3.7 h) by γ-rays irradiating early condensates. Irradiation may have been of solar origin and taking place at the inner edge of the nebular disk. Alternatively, the source of γ-rays could have been one or more supernova(e) exploding in the vicinity of the solar nebula. Such photoexcitation has been experimentally observed, but requires γ-ray photons that have energies in excess of 838 keV. At this stage, we cannot assess whether the Hf isotope composition of the Bulk Silicate Earth differs from that of chondrites, eucrites, and the 4.56 Ga old Martian meteorite ALH84001, and therefore, whether the precursor material for these different planetary bodies received comparable fluences of γ-rays.
U2 - 10.1016/j.gca.2005.09.027
DO - 10.1016/j.gca.2005.09.027
M3 - Journal article
AN - SCOPUS:32944474860
VL - 70
SP - 1261
EP - 1270
JO - Geochimica et Cosmochimica Acta. Supplement
JF - Geochimica et Cosmochimica Acta. Supplement
SN - 0046-564X
IS - 5
ER -