J.B.A.D. van Zon

Target charging in pixe analysis

Abstract The effect of an increased spectral background occurring for PIXE analysis of non-conducting materials has been investigated experimentally. For this purpose the X-ray counting rate as a function of time has been measured under various analysis conditions of thick granite targets. A clear picture of the origin of the increased background can be gathered from the results.

Laboratory EXAFS Spectrometer, Principles and Applications

Abstract In order to be independent of poor availability of synchrotron beamtime a laboratory EXAFS spectrometer has been developed. The X-ray source is a rotating anode generator (max. voltage 60 kV, max. current 300 mA). Monochromatisation and focusing is done with a linear spectrometer, based upon the Rowland circle geometry and a silicon crystal monochromator. High positioning accuracy of monochromator and sample stages are achieved by computer control and position feedback with magnetic rulers. Ionisation chambers monitor incoming and transmitted flux. The spectra of Pt and Na 2 Pt(OH) 6 and their Fourier transforms are compared with the same data taken at SSRL, Stanford (USA). The influence of the resolution on the Fourier transforms has been investigated. The applicability of the apparatus is demonstrated with 6 wt% Bi in LaPO 4 of which the oxygen coordination has been compared to that of Bi in BiPO 4 . As a second example data of Platinum metal particles in ZSM-5 catalyst are presented.

A Linear Spectrometer Designed for EXAFS Spectroscopy

A linear spectrometer, especially designed for EXAFS applications, has been built to maintain the Rowland geometry with the anode focal spot as fixed point on the Rowland circle. The performance of the mechanical construction of this spectrometer allows one to take incremental steps of 5 μm with a resetability of ± 5 μm.

A procedure for optimal determination of trace elements with PIXE

Abstract The parameters that influence the detection limit of small concentrations of a trace element in particle induced X-ray emission analysis are considered. These are: proton-beam intensity, incident particle energy, target thickness, X-ray absorption filter thickness, irradiated target area and the solid angle of detection. The useful range of the parameters, e.g. the exciting beam intensity, is restricted by the maximum target temperature, the highest counting rate which can be handled and by radiation protection safeguards. Taking these restrictions into account the Peak-to-Square-Root-Background ratio (PSRB) has been maximised. The calculations are based on production data for characteristic as well as for bremsstrahlung background radiation reported in the literature. The procedure for parameter optimisation is described and applied for the determination of selenium concentrations in human serum.

An EXAFS Study of a Highly Dispersed Rh/Al2O3 Catalyst

The X-ray absorption spectrum of the Rh K-edge of a highly dispersed reduced Rh/Al2O3 catalyst shows EXAFS oscillations due to Rhodium-Rhodium nearest neighbors. Adsorption of CO at room temperature on the reduced catalyst significantly decreases the amplitude of the EXAFS oscillations. This implies that CO adsorption on very small metal crystallites leads to a disruption of a significant number of the Rhodium-Rhodium metallic bonds.