Age Determination of Meteorites Using Radioactive Nuclides (Special Topic Articles)
Masaharu Tanimizu
Journal of Plasma and Fusion Research 78, 653-658 (2002).
Abstract
Recently, precise isotope ratios of some refractory elements in meteorites are reported using inductively coupled plasma mass spectrometry. In situ decay of 182Hf (T1/2 = 9 Myr), which was produced at the latest nucleosynthesis, are recognized in many meteorites as isotopic anomalies of its daughter isotope, 182W. The degrees of relative 182W isotopic deviation in extra-terrestrial and terrestrial silicate samples vary from +0.3 % to 0 % related to the size of their parent bodies. One ready interpretation of its correlation is the difference in timing of metal-silicate separation in the parent bodies. Between the earth and meteorite parent bodies, the difference is calculated to be about four times of the half-life of 182Hf, equivalent to 36 Myr.
Ce-Nd-Sr isotope systematics of eucrites and lunar rocks
Masaharu Tanimizu and Tsuyoshi Tanaka
in Origin of Elements in the Solar System, Kluwer Academic/Plenum Publishers, New York, NY, pp. 555-572 (2001).
Abstract
138La-138Ce, 147Sm-143Nd and 87Rb-87Sr long-lived decay systems are applied to eucrites and lunar samples to investigate their evolution. Intensive thermal annealings of the Millbillillie eucrite are suggested from a comparison of the Sm-Nd isochron age and the detection of in situ decay of short-lived 146Sm with a younger La-Ce age. The light-REE evolution of lunar rocks, high-Ti mare basalts from A11 and A17 site, and a KREEP basalt is clearly distinguishable from combined isotope systematics of 138Ce and 143Nd. Their different characteristics must have been inherited at an early lunar evolution stage.
Geophysical determination of the 138La β- decay constant
Masaharu Tanimizu
Physical Review C 62, 017601 (2000).
Abstract
The 138La β- decay constant was determined geophysically. The isotopic growth of 138Ce/142Ce and 143Nd/144Nd were examined from ancient igneous crystalline rocks. For the Ce isotope measurement, a newly developed dynamic multicollector technique was applied. The crystallization age of the rocks was calculated to be 2,037±13 Myr from the growth of 143Nd. From the age and the growth of 138Ce, decay constant of 138La β decay was estimated to be 2.37(0.10)x10-12/yr. This value is consistent with those of the latest two gamma-ray counting data of lanthanum compounds within the analytical error.