Sm sbnd Nd sbnd Pu timepieces in the Angra dos Reis meteorite

We have studied Sm sbnd Nd systematics in pyroxene and phosphate mineral separates of Angra dos Reis. A pyroxene-phosphate internal isochron age of T ₂ = 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 10 ⁵. This variation is tentatively assigned to a radiogenic contribution from extinct ¹⁴⁶Sm. 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 of ²⁴⁴Pu with the light REE. Computed ratios ²⁴⁴Pu/Nd are the same in pyroxene and phosphate separates, but ²⁴⁴Pu/ ²³⁸U and ²⁴⁴Pu/ ²³²Th ratios are not. Taking the fission xenon retention age to be 4.55 AE, we obtain an abundance ratio ²⁴⁴Pu/Nd= 1.5 × 10 ^-4 (or an atomic ratio ²⁴⁴Pu/ 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 the ⁸¹Kr- ⁸³Kr method is 55.5 ± 1.2m.y. Neutron capture during the 55.5-m.y. exposure to cosmic rays increased the ratio ¹⁵⁰Sm/ ¹⁴⁹Sm in Angra dos Reis by 6 parts in 10 ⁴.