Canyon Diablo隕鉄中の希土類元素存在度

抄録

Rare earth element (REE) abundances in the Canyon Diablo iron meteorite were determined by the isotope dilution method using thermal ionization mass spectrometry. Isotope ratios of La, Nd, Lu, Ba and Rb were also examined, and they were found to be within the normal range. Because of extremely low REE contents, correction for blank values was necessary even after several distillation of the reagents used. For light REEs, the correction was 50 to nearly 100%, and between 10 and 20% for heavy REEs. The concentrations of REEs in the Canyon Diablo iron meteorite were about 1 to 300ppt, and the normalized values by the Leedey chondrite were approximately 10^-4;. Three REE patterns from one slice showed same positive trend toward heavier REEs, while a different slice showed a negative trend. In the sample, therefore, the REE distribution appears heterogeneous. Ce in the rhenium ribbon of center filament often interfered with the measurements of Ce. Assuming a constant intensity of the interfering beam, the least squares method gave the Ce concentration.