F.O. Borges

Determination of plasma temperature by a semi-empirical method

Doppler or Stark line broadening effects are generally used to determinate plasma temperature. These methods are difficult to apply to spectra of highly ionized atoms due to the short wavelengths involved. It is not at all easy to achieve sufficient wavelength resolution in this spectral range. In this case, a spectroscopic technique based on the relative intensities of lines must be used to measure the electron temperature in a plasma. However the relation of the measure of relative line intensity and the plasma electron temperature is complex and a number of issues must be examined for the diagnostic. In simple cases, only a two levels system need be considered. Here we introduce a semi-empirical method to determine the plasma temperature that takes into account multiple levels structure. In the theoretical model we consider a local thermodynamic equilibrium(LTE). The greatest difficult in the determination of plasma temperature using a multiple levels approach is overcome by calculating the transition probabilities in terms of the oscillator strength parameters. To check the method we calculated the oscillator strengths for the Cu I using a multi-configurational Hartree-Fock relativistic (HFR) approach. The electrostatic parameters were optimized by a least-squares procedure, in order to obtain the best fitting to the experimental energy levels. This method produces gf- values that are in better agreement with their experimental values than the produced by the ab initio calculation. The temperature obtained was 5739.3 K, what is compatible with direct measurements made for cupper DC discharge.

Weighted oscillator strengths and lifetimes for the SVII spectrum

The weighted oscillator strengths (gf) and the lifetimes presented in this work were carried out in a multiconfiguration Hartree-Fock relativistic approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure, in order to improve the adjustment to experimental energy levels. This method produces gf-values that are in better agreement with intensity observations and lifetime values that are closer to the experimental ones. In this work, we presented all the experimentally known electric dipole S VII spectral lines.

Weighted oscillator strengths and lifetimes for the S IX and S X spectra

Abstract The weighted oscillator strengths ( gf ) and the lifetimes presented in this work were carried out in a multi configuration Hartree–Fock relativistic (HFR) approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure, in order to improve the adjustment to experimental energy levels. This method produces gf -values that are in better agreement with intensity observations and lifetime values that are closer to the experimental ones. In this work, we presented all the experimentally known electric dipole S IX and S X spectral lines.

CF-LIBS analysis of frozen aqueous solution samples by using a standard internal reference and correcting the self-absorption effect

The aim of this paper is to present an innovative procedure to determine the composition of a liquid sample using Laser Induced Breakdown Spectroscopy without calibration curves, or the so-called CF-LIBS (Calibration Free-Laser Induced Breakdown Spectroscopy). Our results of CF-LIBS for the elemental composition were compared with the sample standard concentration determined by Microwave Plasma-Atomic Emission Spectroscopy (MP-AES). In this work, a controlled amount of an internal standard, an extra chemical element, is placed into a liquid sample that is afterward frozen to produce a solid target. The plasma of the target material is produced at atmospheric pressure by focusing a Nd:YAG laser on the frozen target surface. Time-resolved emission spectra are acquired and used for quantitative analysis. An extraordinary increase in the accuracy of elemental concentration is achieved when the spectroscopic data are corrected through an analytical elimination of the self-absorption effect. The corrected data plotted in a Boltzmann diagram show that CF-LIBS can provide good analytical sensitivity and accurate and reliable elemental concentrations when the local thermodynamic equilibrium conditions are experimentally fulfilled and the self-absorption effect on the line intensities is corrected. In the case analyzed here, the concentration results obtained by the improved CF-LIBS procedure give relative deviations of 3.3% maximum when compared with those of MP-AES.

Guava flavored whey-beverage processed by cold plasma: Physical characteristics, thermal behavior and microstructure

The present study aimed to compare the physicochemical (pH), physical (rheology parameters and particle size), microstructure (optical microscopy) and thermal properties (differential scanning calorimetry) of guava flavored whey-beverages submitted to cold plama technology in different processing time (5, 10, and 15 min) and gas flow (10, 20, and 30 mL min-1) conditions with a conventional pasteurized product. Whey beverages treated by cold plasma presented higher pH values, lower consistency and lower viscosity, and a flow behavior index similar to Newtonian fluids. Milder cold plasma conditions resulted in whey beverages with higher pH, lower viscosity and consistency, and similar particle distribution and microstructure compared to the pasteurized product. In contrast, more severe processing conditions resulted in a higher particle surface area ([D 3,2]) and smaller particles (~10 μM), due to the decrease in the number of larger particles (1000 μM), cell rupture, the formation of cell fragments, and higher viscosity and consistency. The treatments did not affect the thermal properties (enthalpy and bound water) of any sample.

The study of 3s3p4 configuration in the P-Sequence, Co XIII - Ni XIV, by laser-produced plasmas

Wavelengths from radiation of plasmas produced by a Nd:YAG/glass laser focused on target of Co and Ni have been recorded photographically in the region 240-600 A with a 3m normal incidence spectrograph. For this sequence (Co XIII and Ni XIV) we have identified 13 new lines belonging to the array 3s23p3-3s3p4 and derived 7 new levels for the 3s3p4 configuration. The classification was established by comparison of the relative intensities for the lines along the isoelectronic sequence, extrapolation, and Hartree-Fock calculation.