The direct total evaporation (DTE) method for TIMS analysis

Abstract

The total evaporation (TE) method is an established analytical method for safeguards measurements of uranium and plutonium isotope-amount ratios using thermal ionization mass spectrometry. As fractionation effects are minimized in this analytical method, it is a method of choice in many practical applications that require high accuracy and precision isotope abundance ratio measurements. The speed of signal regulation is a critical parameter for a steady sample evaporation process. Standard TE methods use the data system to read the ion signal and its difference from the target intensity is used to determine the increment in which the filament is heated. The new, hardware-driven proprietary direct total evaporation method uses an analog regulator in the filament power supply with direct feedback of the detector intensity. Only target values are set by the data system initially. The filament heating and sample evaporation process is then carried out by the hardware. The data system just monitors, collects, and calculates the data. Due to the nature of electronic regulation the ion signal is kept stable for the duration of the run until the whole sample is consumed. For routine uranium isotopic analyses of the major isotope-amount ratio n(235U)/n(238U) using a modified MAT261 instrument with SPECTROMAT™ hardware and software upgrades, precision (relative standard deviation, expressed as a percent) and accuracy (relative difference, expressed as a percent) of 0.05 % are obtained for low enriched and high enriched uranium certified reference materials.