Although more than 20 years have passed since the discovery of the debris of
244Pu in meteorites, its application to chronology is not yet fully established. In this paper, several problems involved in
244Pu chronology are discussed in conjunction with those for
129I chronology and the possibility of
244Pu chronology is sought. The most serious problem for
244Pu chronology is the lack of a reference nuclide for
244Pu. Although an ideal nuclide for a reference of
244Pu 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
244Pu/
238U 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
244Pu and
129I chronologies; formation intervals based on
244Pu are about double those from
129I chronology, suggesting that a considerable fraction of
129I was later added to the solar nebula after the end of nucleosynthesis responsible for
244Pu and almost all other nuclides.
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