ION SOURCE CHEMISTRY DURING SIMULTANEOUS ANALYSIS OF THORIUM AND URANIUM BY THERMAL IONISATION MASS SPECTROMETRY (TIMS)

摘要

Thermal ionisation mass spectrometry (TIMS) is conventionally a single element analysis technique and requires the element to be present in the purest chemical form to achieve the ultimate in terms of precision and accuracy in isotope ratios determination. However, in many practical situations, such a condition cannot be satisfied. For example, when Th is irradiated in a nuclear reactor, ~(233)U is produced along with other isotopes of U viz. ~(232)U, ~(234)U, ~(235)U, ~(236)U and ~(238)U. Inspite of the separation and purification of this U from bulk of Th, there would always be small amounts of Th associated with purified fraction of U. Depending upon the separation efficiency, U/Th amount ratio in the purified U fraction would vary and this would alter the ion source chemistry occurring in the thermal ionisation source of the mass spectrometer compared to when the pure forms of U or Th are analysed by TIMS. Hence, it was of interest to study the ion source chemistry of Th and U during their simultaneous analysis by TIMS. This was also considered interesting for developing a TIMS method for determination of ppm levels of ~(232)U in ~(233)U sample obtained by irradiation of ~(232)Th and also for understanding the behaviour of Th during TIMS analysis. This paper presents the results of the studies carried out for the ion source chemistry of U and Th during their simultaneous mass spectrometric analysis by TIMS.