Plasma parameters in atomic-emission spectral analysis of phosphate concentrates of the fission products

Physical parameters of electric arc plasma as well as their time dependences are calculated when analyzing phosphate precipitates of the fission products of irradiated nuclear fuel. Phosphate concentrates of the fission products are known for their complex chemical composition and high thermal and chemical stability. Hence, direct atomic emission spectral analysis of phosphate powders without transferring them into solutions is advisable. Different conditions of sample preparation and synthesis of the reference materials determine the different chemical forms of the elements to be determined. This, in turn, affects the kinetics of their evaporation in the electrode crate and excitation processes in the plasma. The known mechanisms of those processes cannot always be transferred to specific conditions of the given method of analysis thus entailing the necessity of studying the effect of the samples chemical composition on the results of determination, proper choice of spectroscopic carriers, detailed study of spectra excitation processes in spectral analysis, and analysis of the physical parameters of the electric arc plasma. We used the lines Zn I 307.206 nm and Zn I 307.589 nm to measure the effective temperature of the central hot sections of the arc in a range of4500 - 6500 K. NaCl, BaCl2 and NaCl + T1C1 were studied to reduce the effect of the sample elemental composition on excitation conditions of the spectra and their stabilization as a spectroscopic carrier. In control experiments we used carrier-free samples. The coincidence of the values of the plasma physical parameters within the measurement error not exceeding 20%, as well as the identity of the nature of the kinetic curves for samples of phosphate precipitates and synthetic reference materials prove their correctness. The result of the study substantiate correctness of the direct atomic-emission spectral procedure in analysis of phosphate concentrates of fission when using synthetic reference materials.

Spectral interferences and their correction in atomic emission spectral analysis

The main sources of spectral interferences in atomic emission spectral analysis (AESA) are considered, including both wide-range (bremsstrahlung and recombination continuum, radiation of hot condensed particles and electrode ends, scattered light in the spectrometer, overlapping of the analytical line by the wings of the neighbor strong spectral lines of interfering elements, imposition of the components of molecular bands with the very close lines) and narrow-band (partial or complete overlapping of the analytical line with atomic or ionic lines of the sample elements, electrodes and discharge atmosphere; superposition of spectra from higher orders of reflection in conventional diffraction spectrometers and from neighboring orders in two-dimensional echelle spectrometers). The features of their manifestation in various sources of spectrum excitation (flames, DC arc, spark discharges, arc plasma discharges, inductively coupled plasma, microwave plasma, low-pressure electric discharges, laser spark) are considered. The possibilities of reducing the level of spectral interferences or elimination of the spectral noise at the stage of design and manufacturing of AESA devices, as well as upon selecting and adjusting of operation conditions of the analysis are shown. Much attention is paid to the most easily implemented in practice off-peak correction of wide-range spectral interferences. The modern methods of background correction under the spectral peak (under-peak) using a software for atomic emission spectrometers and providing creation of various mathematical models of the background signal in the vicinity of the analytical line at the stage of developing a specific AESA technique are considered. The issues of the choice of spectral lines for analytical measurements, tables and atlases of spectral lines, electronic databases used for this purpose are considered in detail. Specific features of application of the method of inter-element correction with direct spectral overlapping of the lines are given. The operating sequence for taking into account spectral interferences when developing the analysis techniques is proposed.

Methodology of selecting the algorithms for optimization of arc spectral analysis

The goal of the study is the choice of algorithms for optimization of arc atomic emission spectral analysis with MAÉS to elaborate the techniques of quantitative spectral analysis of different objects. The choice of the algorithms is performed on an example of geologic objects with alumosilicate matrix. Determination of the elemental composition of such geological objects is important for obtaining markers, studying geochronological processes, and searching for mineral deposits.