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Search for 248 Cm in the early Solar System
Author(s) -
Lavielle B.,
Marti K.,
Pellas P.,
Perron C.
Publication year - 1992
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1992.tb00219.x
Subject(s) - spallation , xenon , fission , actinide , meteorite , recoil , nuclear physics , radiochemistry , solar system , cosmic ray , chondrite , physics , fission products , natural abundance , isotope , chemistry , neutron , astrophysics , astrobiology
— Possible evidence for the presence of 248 Cm in the early Solar System was reported from fission gas studies (Rao and Gopalan, 1973) and recently from studies of very high nuclear track densities (≥ 5 × 10 g cm −2 ) in the merrillite of the H4 chondrite Forest Vale (F. V.) (Pellas et al ., 1987). We report here an analysis of the isotopic abundances of xenon in F. V. phosphates and results of track studies in phosphate/pyroxene contacts. The fission xenon isotopic signature clearly identifies 244 Pu as the extinct progenitor. We calculate an upper limit 248 Cm/ 244 Pu < 1.5 × 10 −3 at the beginning of Xe retention in F. V. phosphates. This corresponds to an upper limit of the ratio 248 Cm/ 235 U ≤ 5 × 10 −5 , further constraining the evidence for any late addition of freshly synthesized actinide elements just prior to Solar System formation. The fission track density observed after annealing the phosphates at 290 °C (1 hr, which essentially erases spallation recoil tracks) is also in agreement with the 244 Pu abundance inferred from fission Xe. The spallation recoil tracks produced during the 76 Ma cosmic‐ray exposure account for the very high track density in merrillites.