High accuracy measurement of isotope ratios of molybdenum in some terrestrial molybdenites

Molybdenum and lanthanum as alternate burn-up monitors – development of chromatographic and mass spectrometric methods for determination of atom percent fission

A rapid high performance liquid chromatography (HPLC) and thermal ionisation mass spectrometric (TIMS) methods have been developed for the separation and estimation of fission product elements molybdenum and lanthanum for the burn-up measurements on the dissolver solution of Indian pressurised heavy water reactor (PHWR) spent fuel. Reverse phase chromatography method was developed to separate molybdenum from dissolver solution using mandelic acid as mobile phase and a dynamic ion exchange chromatography technique was used for the separation of lanthanum as well as neodymium from a dissolver solution. Sample loading methods which resulted in enhanced ionisation efficiency have been developed for the TIMS analysis of HPLC separated molybdenum and lanthanum fractions. Ascorbic acid mixed with silicic acid in HCl medium was used for loading the molybdenum on to a rhenium filament to obtain stable and intense ion beam. A novel sample loading method for lanthanum in which a mixture of graphite + boric acid (H3BO3) + silica gel was employed to achieve enhanced and steady ion beam formation of LaO+. Concentrations of species of interest were determined employing suitable spikes by isotope dilution mass spectrometry (IDMS) method. The developed methods were adopted for PHWR dissolver solution to establish molybdenum and lanthanum as alternate burn-up monitors. The burn-up data obtained were compared with the well established method of neodymium as fission product monitor. This is a first study of its kind where the data obtained by using molybdenum and lanthanum as fission product monitors were compared with that obtained by Nd-148 method.

High-precision molybdenum isotope analysis by negative thermal ionization mass spectrometry

Procedures for the separation, purification, and high-precision analysis of mass-independent isotopic variations in molybdenum (Mo) using negative thermal ionization mass spectrometry are reported. Separation and purification of Mo from silicate and metal matrices are achieved using a two-stage anion exchange chromatographic procedure. Molybdenum is ionized as the MoO₃ ^- species using a double filament assembly. The MoO₃ ^- ion beams are collected using Faraday cup detectors equipped with a mixed array of amplifiers utilizing 10¹¹ and 10¹² Ω resistors, which allows for in situ measurement and correction of oxygen isobars. The long-term external reproducibility of ⁹⁷Mo/⁹⁶Mo, the most precisely measured Mo isotope ratio, is ±5.4 ppm (2SD), based on the repeated analyses of the Alfa Aesar Specpure ^® Mo plasma standard and using ⁹⁸Mo/⁹⁶Mo for fractionation correction. The long-term external reproducibilities of 92Mo/⁹⁶Mo, ⁹⁴Mo/⁹⁶Mo, ⁹⁵Mo/⁹⁶Mo, and ¹⁰⁰Mo/⁹⁶Mo are ±107, 37, 23, and 32 ppm (2SD), respectively. With this precision, smaller differences in Mo isotopic compositions can be resolved than have been previously possible.

Measurements of extinct fission products in nuclear bomb debris: Determination of the yield of the Trinity nuclear test 70 y later

This paper describes an approach to measuring extinct fission products that would allow for the characterization of a nuclear test at any time. The isotopic composition of molybdenum in five samples of glassy debris from the 1945 Trinity nuclear test has been measured. Nonnatural molybdenum isotopic compositions were observed, reflecting an input from the decay of the short-lived fission products (95)Zr and (97)Zr. By measuring both the perturbation of the (95)Mo/(96)Mo and (97)Mo/(96)Mo isotopic ratios and the total amount of molybdenum in the Trinity nuclear debris samples, it is possible to calculate the original concentrations of the (95)Zr and (97)Zr isotopes formed in the nuclear detonation. Together with a determination of the amount of plutonium in the debris, these measurements of extinct fission products allow for new estimates of the efficiency and yield of the historic Trinity test.

Solvent extraction, ion chromatography, and mass spectrometry of molybdenum isotopes

A procedure was developed that allows precise determination of molybdenum isotope abundances in natural samples. Purification of molybdenum was first achieved by solvent extraction using di(2-ethylhexyl) phosphate. Further separation of molybdenum from isobar nuclides was obtained by ion chromatography using AG1-X8 strongly basic anion exchanger. Finally, molybdenum isotopic composition was measured using a multiple collector inductively coupled plasma hexapole mass spectrometer. The abundances of molybdenum isotopes 92, 94, 95, 96, 97, 98, and 100 are 14.8428(510), 9.2498(157), 15.9303(133), 16.6787(37), 9.5534(83), 24.1346(394), and 9.6104(312) respectively, resulting in an atomic mass of 95.9304(45). After internal normalization for mass fractionation, no variation of the molybdenum isotopic composition is observed among terrestrial samples within a relative precision on the order of 0.00001-0.0001. This demonstrates the reliability of the method, which can be applied to searching for possible isotopic anomalies and mass fractionation.