SmNdPu timepieces in the Angra dos Reis meteorite
1977; Elsevier BV; Volume: 35; Issue: 2 Linguagem: Inglês
10.1016/0012-821x(77)90131-5
ISSN1385-013X
Autores Tópico(s)Nuclear Physics and Applications
ResumoWe have studied SmNd systematics in pyroxene and phosphate mineral separates of Angra dos Reis. A pyroxene-phosphate internal isochron age ofT2 = 4.55 ± 0.04AE is obtained, in excellent agreement with reported Pb-Pb ages.142Nd/144Nd ratios in pyroxene samples are systematically larger than those in phosphates by 6 parts in 105. This variation is tentatively assigned to a radiogenic contribution from extinct146Sm. Fission xenon components in pyroxene and phosphate separates are characterized by discrete ratios of fission/spallation and evidence is presented for a third ratio in celsian. It is shown that this characteristic is due to a close association of244Pu with the light REE. Computed ratios244Pu/Nd are the same in pyroxene and phosphate separates, but244Pu/238U and244Pu/232Th ratios are not. Taking the fission xenon retention age to be 4.55 AE, we obtain an abundance ratio244Pu/Nd= 1.5 × 10−4 (or an atomic ratio244Pu/150Nd= 1.6 × 10−3) at this time and in the region of the solar system where the Angra dos Reis parent body formed. The exposure age of Angra dos Reis, as obtained by the81Kr-83Kr method is55.5 ± 1.2m.y. Neutron capture during the 55.5-m.y. exposure to cosmic rays increased the ratio150Sm/149Sm in Angra dos Reis by 6 parts in 104.
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