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Abstract No.: MoP-LB8
Session: LATE-BREAKING/Inductively Coupled Plasma MS/Inorganic MS
Presentation date: Mon, Aug 28, 2006
Presentation time: 14:30 – 16:00

Thermal Ionisation Mass Spectrometric Studies on Thorium and Uranium in Irradiated Thoria Fuel

Devanathan Alamelu1, Suresh Kumar Aggarwal1, R. Govindan1, P. G. Jaison1, P. S. Khodade1, V. L. Sant1, Pravin M. Shah1

1 Bhabha Atomic Research Centre, Mumbai, India

Correspondence address: Devanathan Alamelu, Bhabha Atomic Research Centre, Fuel Chemistry Division, Trombay, Mumbai, 400 085 India.

Keywords: Ionization, Thermal; Isotope Dilution; Isotope Ratio MS; Mass Spectrometry, Isotope Ratio.

Novel aspect: Atomic na molecular ion formation in TIMS of thorium and uranium.


Thermal Ionization Mass Spectrometry (TIMS) is a useful analytical technique for determining the amounts of different isotopes of an element. By using the principle of isotope dilution, the total amount of the element present in a complex matrix can also be determined with high precision and accuracy. This has advantage due to the fact that the results are not affected by incomplete recovery of the element from a complex matrix such as irradiated thoria fuel sample. Further, since the determination of total amount of an element (Th or U in the present case) involves the measurement of the amount ratios of two isotopes in the spiked sample, the matrix effects are practically non-existent in ID-TIMS.

In view of the utilization of Th in nuclear power programme in India, it was essential to develop thermal ionization mass spectrometric methodology for carrying out the measurements on Th and U in irradiated thoria fuel samples. Studies were performed on the formation of atomic (M+) and molecular (MO+) ions of Th and U, when present together (Th/U amount ratio about 70) on the same filament of a double filament assembly, by varying heating temperatures of ionization and vaporization filaments (of high purity rhenium). It was observed that UO+ ion appears at much lower vaporization filament heating current (about 1.7A) compared to ThO+ which appears at much higher vaporization filament heating temperature (about 3 A). Further, the intensity of Th+ ion was negligibly small under the conditions of obtaining sufficient U+ ions. These differences were attributed to differences in the vaporization characteristics of oxides of U and Th and their ionization potentials. Using the optimized parameters of heating the vaporization and ionization filaments, it was possible to carry out isotope ratio determinations of Th and U. 229Th milked from aged 233U and a chemical assay reference material of natural U (NIST-SRM-950) were used as tracers in isotope dilution for determining the concentrations of Th and U, respectively, in the irradiated fuel sample. This paper presents the highlights of the work carried out on ion source chemistry of Th and U and the results obtained on one of the irradiated fuel samples of thoria.