TXRF analysis using polycapillaries

SÁNCHEZ, H.J.; PEREZ, R.D.; CARVALHO, M.L.; RUBIO, M.

Gotenburg, Suecia

Conferencia; 13th conference on Total Reflection X-Ray Fluorescence Analysis and Related Methods; 2009

University of Gothenburg

Recently, the capabilities of the x-ray fluorescence (XRF) and micro-x-ray fluorescence spectroscopy (mXRF) were expanded by the use x-ray lenses. At present, most of the x-ray lenses used in XRF experiments are mainly glass capillaries and polycapillaries. Glass capillaries are small tapered tubes in which photons travel along the capillary by total reflection on the inner wall. Polycapillaries are more complex systems formed by hundred or, usually, thousands of monocapillaries that accept photons from an emitting point and concentrate the emerging photons in a focal spot. Semi-lens polycapillaries or double-focus polycapillaries are used in different geometries. Semi-lens polycapillaries are special lenses than collect photons from a focal spot and produce an emerging parallel beam, and conversely, collect photons from a parallel beam and concentrates the photons in a focal spot. These kings of lenses are particularly appropriated to perform total reflection x-ray fluorescence analysis because their capability of producing a homogeneous beam with very low divergency. In this work we performed TXRF measurements in different samples using conventional TXRF systems and especial setups using polycapillaries. A Mo x-ray tube with a 3kW power supply was used as excitation source, and a high resolution angular stage was used for TR positioning. The detection system consists of a Si-PIN detector, a fast amplifier and a standard multichannel analyzer  In order to perform a direct comparison of the different method employed, the same samples and reflectors were used in all the measurements. By means of the calculation of minimum detection levels the methods tested in this work were intercompared. As general conclusions, we verified that the use of polycapillaries facilitates the alignement and the setup of the experiment as much as beam-guide does. The natural band-pass nature of polycapillaries improves the excitation conditions as compared with white-beam excitation, and so, contributes to reduce the background. On the other hand, the intensity of photons on the samples when polycapillaries are employed is lower than in other configurations, which produces a lost of eficiency for the excitation of the sample.