A New Series of Uranium Isotope Reference Materials for Investigating the Linearity of Secondary Electron Multipliers in Isotope Mass Spectrometry

Abstract

A new series of gravimetrically prepared uranium isotope reference materials, the so-called IRMM-074 series, with the n(235U)/n(238U) isotope ratio held constant at unity and the n(233U)/n(238U) isotope ratios varying from 1.0 to 10-6 has been prepared and certified. The methods for the preparation, the mixing and the certification are described. Additionally, recent observations regarding the linearity response of secondary electron multipliers (SEM) and suitable reference materials for investigating detector linearity are reviewed. Two measurement procedures for applying the IRMM-072 and IRMM-073 (diluted from the remaining fraction of IRMM-072) series as well as the new IRMM-074 series for assessing SEM linearity are described. The procedures are tailor-made for the specific instrumental characteristics of Thermal Ionization Mass Spectrometers (TIMS) and Multiple-Collector Inductively Coupled Plasma Mass Spectrometers (MC-ICPMS) but can be adapted also for further types of isotope ratio mass spectrometers.