230Th/234U/238U and 231Pa/235U ages from a single fossil coral fragment by multi-collector magnetic-sector inductively coupled plasma mass spectrometry

Separate fractions of U, Th, and Pa are measured by employing a multi-dynamic procedure, whereby 238U is measured on a Faraday cup simultaneously with all minor isotopes measured with a Daly ion counting detector. The multi-dynamic procedure also permits correcting for both the Daly to Faraday gain and for mass discrimination during sample analyses. The analytical precision of 230Th/234U/238U and 231Pa/235U dates is generally better than ±0.3% and ±1.5%, respectively (2 Relative Standard deviation [RSD]). Additional errors resulting from uncertainties in the decay constant for 231Pa and from undetermined sources currently limit the 231Pa/235U age uncertainty to about ±2.5%. U isotope data and 230Th/234U/238U ages agree with National Institute of Standards and Technology (NIST) reference materials and with measurements made by Thermal Ionization Mass Spectrometry (TIMS) in our laboratory.