An Inter‐Laboratory Assessment of the Thorium Isotopic Composition of Synthetic and Rock Reference Materials

We present a concerted international effort to cross‐calibrate five synthetic Th isotope reference materials (UCSC Th “A”, OU Th “U”, WUN, IRMM‐35 and IRMM‐36), and six rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR‐2, USGS W‐2, USGS BHVO‐2, LV18) using multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS). We then compare our new values with a compilation of literature mass spectrometric data for these reference materials and derive recommended “consensus” 230 Th/ 232 Th values for each. We also present isotope dilution U and Th concentration data for four rock reference materials (UCSC TML, Icelandic ATHO, USGS BCR‐2, USGS W‐2).