Eva Selin

Background reduction of x-ray fluorescence spectra in a secondary target energy dispersive spectrometer

Abstract Improved peak-to-background ratios for trace element analysis have been obtained in a conventional spectrometer. The integrated number of background counts is ∼0.5% of the high energy scattered radiation.

Application of an Energy Dispersive X-Ray Fluorescence Spectrometer to Air Pollution Studies

A secondary target Energy Dispersive X-ray Fluorescence spectrometer with three axial geometry has been used in multielement analysis of aerosols. A new type of monitoring system has been designed to monitor the flow of secondary photons and thus minimize the influence of time variation in the X-ray intensity. The aerosols were divided in two size fractions by means of a virtual impactor and deposited on filters. The absolute concentrations of the different elements were obtained by use of standard samples with known element concentrations. Detection limits for sixteen elements are given and are in the order of ng per cm2. The method has been applied to aerosols of widely varying composition and concentration in ambient atmosphere and industrial environment.

HIGH-SPIN ROTATIONAL STATES IN

Levels within three rotational bands in the odd A nuclide 169Yb have been excited in the 167Er(α,2n)169Yb reaction. The positive parity ground-state band is strongly perturbed. The observed energy levels and relative transition rates within this band are compared with the results of a Coriolis coupling calculation. Good agreement is obtained if the theoretical Coriolis coupling strength is reduced for the orbitals close to the Fermi surface. With gs = gsfree and non-adiabatic wavefunctions the experimental E2/M1 mixing ratios are reproduced for the 7/2+ [633] ground-state band. The magnetic moment for the ground-state has been calculated and is compared with the measured one for the isotone 167Er. This comparison indicates that the mechanism which reduces the Coriolis matrix elements may also be effective in preventing interband M1 transitions with |ΔK| = 1. The results of a Coriolis coupling calculation for N = 5 bands are also discussed. The rotational levels in the doubly-even nuclides 168Yb and 170Yb are observed up to the 10+ member.

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A number of preparations of cytochrome oxidase have been analyzed for metals by energy dispersive X-ray fluorescence spectrometry. The EPR characteristics, the peptide compositions, the protein and phospholipid contents as well as the catalytic constants of the samples have also been determined. It is confirmed that the enzyme functional unit contains three copper atoms and one zinc atom in addition to two iron atoms. On the basis of the parameters determined for the different samples it is suggested that a high catalytic activity of a preparation can be correlated to a number of other analytical characteristics.

Yb,

Abstract In situ flight measurements of accumulation mode aerosol particles were performed in the upper troposphere during the 1991/1992 EASOE (European Arctic Stratospheric Ozone Experiment). On-line number size distributions were obtained by using an optical particle counter, the PMS LAS-X. Support data, like ozone mixing ratios, and meteorological as well as flight parameters were collected simultaneously. The present study analyses the particle sampling system used aboard the Transall aircraft. A correction algorithm for particle losses and sizing errors is developed based on calculations. A corrected number size distribution is compared with measurements reported in the literature.

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Concentrations of particulate bromine and lead have been measured during one summer and one winter period. The measurements were made simultaneously in five sites in a city on the Swedish west coast. A rural site about 60 km from the city was used to measure the background aerosol. Aerosol sampling was made with six dichotomous virtual impactors, which fractionate the aerosol into two modes, one fine particle mode (aerodynamic diameter, a.d. < 3.5 μm) and one coarse particle mode (3.5 μm < a.d. < 18 μm). The aerosol was collected onto thin teflon filters. Element concentrations were obtained by Energy Dispersive X-Ray Fluorescence Analysis. The element concentrations were related to air mass trajectories. The Br/Pb ratio proved to be the same on a given date for the city sites and the background site. A dependence on the air mass history was found, suggesting that it is the quality of the air basin in the region that influences the Br/Pb ratio even for fresh car exhaust. The Br/Pb ratio was the same for fine and coarse particles, indicating that the ratio is determined before coagulation with larger particles occur. The ratios between coarse and fine particles containing lead and bromine respectively were also studied. The results suggest that lead and bromine are actually attached to the same particles.

Yb, AND

Abstract A system for trace elemental analysis by X-ray spectrometry has been developed. The system consists of a secondary fluorescence low power X-ray tube, a Si(Li) detector with associated pulse processing system and minicomputer. The spectrometer has been used for routine analysis of blood specimens.

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The background levels in X-ray spectra from a Si(Li) detector have been studied in two different ways. First, an increasingly larger area of the detector was irradiated and significant changes in the resulting spectra were observed. Secondly, the detector was scanned across a diagonal and the detection efficiency was measured. Both methods showed that the active area as given by the manufacturer was significantly larger than that which could be irradiated without degradation of X-ray spectra. Furthermore, it is shown that the detector performance changed drastically with the time since the bias was applied. Artefacts and a general increase in the background reduced the usable detector area with 20% after twelve hours. In a normal analysis this gives rise to an increase in detection limits of up to 65% for an aerosol sample as compared to the detection limits when bias just has been applied.

Yb.

Time dependent background and artefacts in X-ray Fluorescence spectra have been studied with a fine X-ray beam close to the edge of the active area of a Si(Li) detector. The results indicate that polarisation takes place in this region of the detector under the influence of the bias. When the detector has been biased for several hours and is irradiated with photons in the 10-20 keV range the background decays with time constants in the order of 30 s and 1 h.

Analytical characterization of cytochrome oxidase preparations with regard to metal and phospholipid contents, peptide composition and catalytic activity.

Photon excited X-ray fluorescence has been used for quantitative trace element analysis in thick organic specimens. The evaluation of matrix effects has been facilitated by use of a PDP-11 computer which can be connected on line to the data collecting system. The handling of blood serum samples is discussed.