Total Evaporation Method Research Articles

Evaluation of the n( 235U)/ n( 238U) isotope ratio measurements in a set of uranium samples by thermal ionization mass spectrometry

The measurement of n( 235U)/ n( 238U) isotope amount ratio in a set of representative uranium samples with enrichment levels ranging from 0.5 to 20.0 wt.% of 235U was carried out by thermal ionization mass spectrometry using the traditional and the total evaporation methods. The uncertainties of the measurement results were evaluated according to the recommendations of the ISO guide to the expression of uncertainty in measurement. They were then compared to the requirements of the IAEA international target values for measurement uncertainties in safeguarding nuclear materials.

Use of Thermal Ionization Mass Spectrometry for Measuring the Oxygen Isotope Ratio in Uranium Oxides1,2

A method was developed for precise determination of oxygen isotope ratios in uranium oxides. Thermal ionisation mass spectrometry (TIMS) was used for direct measurements of n(U18O+)/n(U16O+) using the molecular species UO+. Suitable sample handling and filament preparation techniques were developed in order to obtain reproducible results and avoid oxygen contamination. The actual measurements were performed using the total evaporation method. By this technique the achieved precision for n(U18O+)/n(U16O+) measurements was in the range of 0.04%. The peak jump techniques was also used for measurements, and the results of both techniques are discussed. The TIMS measurement are verified by comparative measurements using secondary ion mass spectrometry (SIMS).

Calibration procedures for a multicollector mass spectrometer for cup efficiency, detector amplifier linearity, and isotope fractionation to evaluate the accuracy in the total evaporation method

The procedure used for the evaluation of the cup efficiency factors of a multicollector mass spectrometer is described and results are given that were obtained with three different isotopes ( 187Re, 238U, and 239Pu). A check of the linearity of the detector amplifier system including the Faraday cup itself is described using the uranium reference material of IRMM (Institute for Reference Materials and Measurements) series 072. These reference materials allow the determination of the mass fractionation on the 235U/ 238U ratio to correct the 233U/ 235U ratio which is used to check the linearity of the whole system at different ion intensities. The correction factors determined through these procedures were applied to the results of isotope analyses obtained by total evaporation in order to evaluate the magnitude of residual biases. The mass spectrometer used for these tests is a 12 year old Finnigan MAT 261 with nine fixed Faraday collectors in a configuration allowing simultaneous measurement of all uranium and plutonium isotopes.

Total evaporation measurements: experience with multi-collector instruments and a thermal ionization quadrupole mass spectrometer

Results and experience are presented for a method of “fractionation free” measurements in thermal ionization mass spectrometery. The method can be used not only on multi-collector mass spectrometers, where the isotopes of interest can be measured simultaneously, but also on a thermal ionization quadrupole mass spectrometer using a special scanning and heating sequence. The total evaporation method strongly decreases the errors due to uncorrected fractionation when the amount of sample loaded on the filament varies widely. Resin beads containing only 1 ng of U and/or Pu can also be analyzed. The performance is demonstrated on uranium and plutonium samples.

Report on preliminary experience with total evaporation measurements in thermal ionization mass spectrometry

Results and experience are presented for a method of “fractionation bias free” measurements in thermal ionization mass spectrometry. The total evaporation method can be performed on multi-collector mass spectrometers where the isotopes of interest can be detected simultaneously. The total consumption of the sample allows one to use filament loadings of different amounts without having calibration problems due to fractionation. The performance of this method is demonstrated on uranium and plutonium samples.