Manoj Kumar Saxena

Studies on the evaporation and ionisation behaviour of uranium and plutonium in thermal ionisation mass spectrometry

Studies are reported on the evaporation and ionisation behaviour of uranium (U) and plutonium (Pu) under conditions of their simultaneous mass spectrometric analyses using a double rhenium filament assembly, a multicollector Faraday cup detector system and a synthetic mixture of SRM-200-U and SRM-947-Pu with the U/Pu ratio as 10. The U+ and UO+ ions start appearing at an evaporation filament temperature lower than that for appearance of Pu+. However, the ion current of Pu+ is 5-10 times greater than that of U+. The coexistence of oxides of Pu and U on the evaporation filament appears to enhance the stability of UO+. Two different approaches are compared to account for Pu-238 isobaric interference at U-238 during simultaneous isotopic analyses of U and Pu from the same filament loading. The K factor values for U and Pu during their simultaneous mass spectrometric analyses are lower compared with those observed previously when U and Pu are analysed from separate filament loadings with chemically pure fractions of each.

INVESTIGATIONS FOR ISOBARIC INTERFERENCE OF 238PU AT 238U DURING THERMAL IONIZATION MASS SPECTROMETRY OF URANIUM AND PLUTONIUM FROM THE SAME FILAMENT LOADING

Three different methodologies are reported for circumventing the isobaric interference of 238Pu at 238U during simultaneous thermal ionization mass spectrometric analysis of U and Pu. These are as follows: (i) obtaining the 235U238U amount ratio at lower evaporation filament current and hence eliminating the need for any isobaric interference correction due to 238Pu at 238U; (ii) determining the 240Pu239Pu amount ratio at lower evaporation filament current during the optimization of the ion current of U+ and Pu+ and calculating the 238Pu239Pu amount ratio of the unknown sample; (iii) optimizing the evaporation filament heating current for simultaneous mass spectrometric analysis of U and Pu and using the 240Pu239Pu amount ratio obtained from the first 2–3 blocks to arrive at the 238Pu239Pu atom ratio required in the interfering element correction (IEC) approach. The three methodologies described are useful for either (a) completely eliminating the need to know the 238Pu239Pu amount ratio or (b) determining the 238Pu239Pu amount ratio from the same filament loading prior to performing simultaneous mass spectrometric analysis. The drawbacks and advantages of each of the methodologies are discussed with respect to the accuracy of the data and the time of analysis. It is shown that the last methodology along with the IEC approach provides a universal solution to correct for the isobaric interference of 238Pu at 238U in all the unknown samples. The studies were carried out by using the conventional method of loading nitrate solutions of U and Pu, a double rhenium filament assembly, a multicollector Faraday cup detector system and employing synthetic mixtures of SRM-200-U and SRM-947-Pu with varying UPu ratios.

Simultaneous preconcentration of uranium and thorium in aqueous samples using cloud point extraction

Uranium (U) and thorium (Th) are both chemically and radiologically toxic even at ultratrace concentrations. Hence, the development of new preconcentration procedures for their precise determination by simple, versatile and cost effective analytical techniques is desirable. A novel, simple and simultaneous cloud point extraction (CPE) procedure has been developed for preconcentrating trace amounts of U and Th in aqueous samples. Preconcentration of the metal ions in the surfactant rich phase of Triton X-114 was carried out by complexing them with trioctylphosphine oxide (TOPO) and N,N,N′,N′-tetraoctyldiglycolamide (TODGA). The preconcentrated solution was subjected to UV-visible spectrophotometry employing arsenazo-III. Partial least square regression analysis was then utilized to resolve their overlapping absorbance spectra and thereby allowing their determination in the presence of one another. The CPE procedure was optimized with respect to: pH of the solution, ionic strength, extraction temperature, phase separation temperature and concentrations of extractants, surfactant and co-surfactant. The developed CPE procedure resulted in percentage extraction efficiencies (EEs) of 98.0 ± 0.5 for U and 99.5 ± 0.5 for Th. Interference studies were also carried out and it was found that the recoveries of U and Th were 98% and 99% respectively in the absence of and ≥95% in the presence of interfering ions. The linear dynamic concentration ranges of the procedure were found to be 15–1000 ng mL−1 and 10–1000 ng mL−1 for U and Th, respectively. The developed methodology was successfully employed for the determination of U and Th in unspiked and spiked samples of ground water, lake water and sea water with ≤4% relative standard deviations. These samples were also directly analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and the agreement between these two results at the 95% confidence level validates the developed methodology. The proposed CPE procedure can be used effectively for the simultaneous extraction of U and Th quantitatively with PFs of 94 for U and 100 for Th and can tolerate much higher levels of interfering ions.

Determination of plutonium by alpha spectrometry

Determination of actinides in the environmental and bioassay samples is important in view of the following factors: increasing energy production by nuclear reactors; environmental contamination due to fallout from nuclear weapons testing and burn up of nuclear-powered satellites; the growing emphasis on the desirability of a cleaner environment; and public concern over the potential hazards associated with nuclear reactors. Among the various actinides, plutonium is one of the most important due to the large amounts produced in the nuclear fuel cycle. Further, the extremely low levels of plutonium in the different biological and environmental samples demand the development of precise, accurate, and sensitive methods to arrive at meaningful conclusions from the results obtained in various studies. In addition to various other techniques available, alpha spectrometry is commonly used.

Determination of trace impurities in advanced metallic nuclear fuels by inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS)

Binary and/or ternary metallic alloys of uranium (U) and plutonium (Pu) with transition metals are considered to be promising fuels for fast breeder reactors due to their high fissile atom content, high breeding ratio with lower doubling time, dimensional stability at high burn-up and high thermal conductivity, etc. Hence, the development of new and promising analytical methodologies for the characterization of trace impurities in advanced metallic fuels is always appreciated. In the present work, a number of trace impurities viz., B, Ce, Cd, Co, Eu, Dy, Gd, Mn, Nd, Ni, Sm and Tb in U–Ti, U–Zr and U–Mo alloys were determined by inductively coupled plasma mass spectrometry (ICP-MS). Solvent extraction using tributylphosphate (TBP) in carbon tetrachloride (CCl4) was used for the partial removal of matrix elements so as to reduce the matrix effect on these analytes during mass spectrometric analysis. The common analyte internal standard (CAIS) technique was refined and utilized to account for the effect of the remaining matrix elements. The proposed refined CAIS technique was validated by standard addition using synthetic samples and the analyte recoveries were found to be ≥92%. Real samples of U–Ti, U–Zr and U–Mo alloys were analyzed for trace elements and the relative standard deviations (RSDs) were found to be between 5 and 8%. Cross-validation of the proposed method was carried out by isotope dilution mass spectrometry (IDMS) and recovery studies employing gamma spectrometry. The method detection limit (MDL) lies in the range of 3–15 ng mL−1.

Preparation and characterization of234U for mass spectrometry and alpha-spectrometry

Abstract234U of high isotopic purity (>99 atom%) as well as of high radiochemical, purity was separated from aged238Pu prepared by neutron irradiation of237Np. Methodologies based on ion exchange and solvent extraction procedures were used to achieve high decontamination factor from238Pu owing to the very high α-specific activity of238Pu (2800 times) in comparison to that of234U. Isotopic composition of purified234U was determined by thermal ionisation mass spectrometry. Alpha spectrometry was used for checking the radiochemical purity of234U with respect to concomitant α-emitting nuclides. The separated234U will be useful for different investigations using mass spectrometry and alpha spectrometry.

Selective micellar extraction of ultratrace levels of uranium in aqueous samples by task specific ionic liquid followed by its detection employing TXRF spectrometry

A task specific ionic liquid (TSIL) bearing phosphoramidate group, viz., N-propyl(diphenylphosphoramidate)trimethylammonium bis(trifluoromethanesulfonyl)imide, was synthesized and characterized by 1H NMR, 13C NMR, 31P NMR, and IR spectroscopies, elemental (C H N S) analysis, and electrospray ionization mass spectrometry (ESI-MS). Using this TSIL a cloud point extraction (CPE) or micelle mediated extraction procedure was developed for preconcentration of uranium (U) in environmental aqueous samples. Total reflection X-ray fluorescence spectrometry was utilized to determine the concentration of U in the preconcentrated samples. In order to understand the mechanism of the CPE procedure, complexation study of the TSIL with U was carried out by isothermal calorimetric titration, liquid-liquid extraction, 31P NMR and IR spectroscopies, and ESI-MS. The developed analytical technique resulted in quantitative extraction efficiency of 99.0 ± 0.5% and a preconcentration factor of 99 for U. The linear dynamic range and method detection limit of the procedure were found to be 0.1-1000 ng mL-1 and 0.02 ng mL-1, respectively. The CPE procedure was found to tolerate a higher concentration of commonly available interfering cations and anions, especially the lanthanides. The developed analytical method was validated by determining the concentration of U in a certified reference material, viz., NIST SRM 1640a natural water, which was found to be in good agreement at a 95% confidence limit with the certified value. The method was successfully applied to the U determination in three natural water samples with ≤4% relative standard deviation (1σ).

Microwave-assisted dissolution of highly refractory dysprosium-titanate (Dy2TiO5) followed by chemical characterization for major and trace elements using ICP-MS, UV-visible spectroscopy and conventional methods

Abstract Dysprosium-titanate (Dy2TiO5), being highly refractory in nature, its dissolution using conventional (hot-plate and fusion) methods is very difficult. Hence, for quantitative dissolution, a microwave method has been developed. The instrumental parameters and amount of acids has been optimized. Studies have been carried out for precise and accurate estimation of major elements such as Dy, Ti, and Mo. An anion exchange column has been used to separate Mo, Dy and Ti. Analysis of these elements has been carried out using ICP-MS, UV-visible spectroscopy, and gravimetric methods. In the developed method, precipitation of molybdenum and dysprosium has been done using α-benzoine oxime, and oxalic acid respectively. These precipitates have been converted into their respective oxide form. The purities of these oxides (Dy2O3 and MoO3) have been determined using ICP-MS. The method has been validated using synthetic samples where it is found that accuracy of Dy and Mo is >99% and precision is <1 (%RSD). The titanium has been determined using UV-visible spectroscopy with accuracy >98% and precision <2 (%RSD).