Meteoritic 138Ce/142Ce ratio and its evolution

Tsuyoshi Tanaka, H. Shimizu, Akimasa Masuda

doi:10.1038/307251a0

The nuclide 138La decays to 138Ce and 138Ba by β− and electron capture, respectively, with a total half life of about 1×105 Myr. Rankama1 suggested the possibility of age determination using this radioactive decay system. Recently, Tanaka and Masuda succeeded in age determination by using the 138La–138Ce geochronometer for a gabbro from the Bushveld complex, South Africa. This La–Ce isotopic system, coupled with the Sm–Nd system, provides a new isotope tracer2,3 for the geo- and cosmochemical samples, especially for samples having a Ce anomaly in the rare-earth element patterns. Meteoritic primordial composition of cerium isotopes can serve as a basis for La–Ce systematics. Furthermore, Ce isotopic compositions for meteorites will provide information concerning half-life data of the 138La decay system, which remains uncertain. Here, cerium isotope ratios were determined for Juvinas, Pasamonte and ALH-78132 eucrites and the Jilin (H4) chondrite. Neodymium isotope ratios and abundances of lanthanum, cerium, neodymium and samarium were also determined for these meteorites.

Meteoritic 138Ce/142Ce ratio and its evolution

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