Precise measurement of cerium and lanthanum isotope ratios.

Abstract

The isotope ratios of cerium and lanthanum are determined precisely by a surface ionization mass spectrometer. 138Ce/142Ce and 140Ce/142Ce ratios for Ce standard solution are 0.0225762± 0.0000014 (2σ) and 7.9471±0.0003 (2σ), normalized to 136Ce/142Ce=0.01688, respectively. 138La/139La ratio is 0.0009025±0.0000005 (2σ). The oxygen isotope ratios in measurements of REE as oxide ions are 0.0003916±0.0000014 (2σ) and 0.002129±0.000010 (2σ) for 17O/16O and 18O/16O. The isotopic abundances (%) of 136Ce, 138Ce, 140Ce and 142Ce are calculated to be 0.1878, 0.2512, 88.433 and 11.128, respectively. The isotopic abundances (%) of 138La and 139La are calculated to be 0.09016 and 99.9098. These isotopic abundances obtained here give the following relation: (138La/142Ce)ATOMIC=0.008173×(La/Ce)WEIGHT. These precise isotopic abundances on Ce and La are fundamental values in a La-Ce geochronometer