Plutonium, uranium and rare earths in the phosphates of ordinary chondrites—the quest for a chronometer

摘要: Abstract The distributions of Pu, U and the REE (in particular Nd) in single crystals calcium phosphates, merrillite apatite, ordinary chondrites were studied to establish whether 244 Pu can be used determine time differences meteorite formation. Uranium was measured by an induced-fission track technique secondary ion mass spectrometry. Limits on concentrations (at retention) inferred from fossil measurements. It is argued here that most previous estimates concentrations, obtained tracks failed correct adequately for spallation-induced probably not correct. Plutonium preferentially enriched relative apatite. In contrast, are average 15 times higher apatite than merrillite. There grain variations, same phosphate phase a given meteorite, both elements. On other hand, remarkably constant (typical variations type 5 6 cases less 10%). Average Nd different range 96 164 ppm. abundances show more variations. 13 8 54 ppm ratios 2.7 11. Despite affinity there no quantitative correlation between these elements grains chondrite. Because this lack geochemical coherence any REE, it concluded cannot formation chondrites. Bulk measurements avoid problems associated with discussed, however they have so far proven little utility.