Secondary ion mass spectrometry for the measurement of 232Th/230Th in volcanic rocks

A technique is presented for the determination of Th-232/Th-230 in volcanic rocks by secondary ion mass spectrometry (SIMS). The technique utilizes a large format high-resolution, high-transmission ion microprobe, the Cameca IMS 1270. Although samples of chemically separated Th are required. these samples demand no special treatment in addition to that already utilized in thermal ionization mass spectrometry. This SIMS technique has considerable advantages in terms of sample size requirement, ease of sample loading, and rapidity of analysis over existing techniques, while providing an overall reproducibility of 0.5%-1.0%. Replicates of standard reference materials and rock materials already characterized by other techniques show excellent agreement with established values, supporting the reliability and accuracy of this new method. (C) 2000 Elsevier Science B.V.