Rapid and accurate U/Th dating using parallel ion-counting multi-collector ICP-MS

Abstract

Using the parallel ion-counting capability of an appropriately configured multi-collector ICP-MS it is possible to simultaneously measure the activity ratios 230Th/234U and 234U/238U in a single solution. A method has been developed which fully internalises the measurement of elemental fractionation, instrument mass bias and ion counter gain, allowing on-line calculation of U/Th ages on a cycle-by-cycle basis during data acquisition. Because of the high efficiency of this technique very small sample sizes can be used, with permil-level precision possible on both 230Th/238U and 234U/238U from analyses of a few tens of nanograms of uranium. As U and Th fractions do not need to be collected and..