^<244>Pu年代法の可能性と問題点

概要

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Although more than 20 years have passed since the discovery of the debris of ^<244>Pu in meteorites, its application to chronology is not yet fully established. In this paper, several problems involved in ^<244>Pu chronology are discussed in conjunction with those for ^<129>I chronology and the possibility of ^<244>Pu chronology is sought. The most serious problem for ^<244>Pu chronology is the lack of a reference nuclide for ^<244>Pu. Although an ideal nuclide for a reference of ^<244>Pu is not available, however, individual candidates for a reference element are proposed for several specific samples, e.g., uranium or rare earth elements (REE's) for bulk chondrite samples and light REE's for the acid-residual fraction of the most primitive ordinary chondrites. Using the literature values of ^<244>Pu/^<238>U and the nucleosynthesis model by Fowler (1987), formation intervals are calculated for several meteorite specimens. There appears to be an apparent discrepancy in calculated ages between ^<244>Pu and ^<129>I chronologies; formation intervals based on ^<244>Pu are about double those from ^<129>I chronology, suggesting that a considerable fraction of ^<129>I was later added to the solar nebula after the end of nucleosynthesis responsible for ^<244>Pu and almost all other nuclides.
日本地球化学会の論文
1993-11-05