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Th. Meinschad, C. Streli, P. Wobrauschek, C. Eisenmenger-Sittner:
"A NEW WINDOWLESS SI ANODE FINE FOCUS X-RAY TUBE FOR THE MORE EFFICIENT EXCITATION OF LOW Z ELEMENTS IN TXRF ";
Poster: Denverx-Ray Conference, Colorado Springs, USA; 2002-07-29 - 2002-08-02.

A NEW WINDOWLESS SI ANODE FINE FOCUS X-RAY TUBE FOR THE MORE EFFICIENT EXCITATION OF LOW Z ELEMENTS IN TXRF

Th.Meinschad1, Christina Streli1, P.Wobrauschek1, Ch. Eisenmenger-Sittner2,
1Atominstitut, Univ. of Technology, Vienna, Austria
2 Inst. of condensed matter, Vienna Univ.of Technology, Austria


To excite low Z elements efficiently low energy photons just above the absorption edge of the element to be analyzed are required. Especially to detect Al and Na on Si wafer surfaces, photons with an energy below the Si ?K edge but above the Al-K edge are needed to avoid a strong excitation of the Si bulk but giving efficient excitation of the analytes. Using synchrotron radiation is the most effective way but also for lab scale instrumentation there are some approaches. Besides W-M lines also the use of Si K line is possible. An additional problem is the fact that total reflection geometry requires a collimated beam, so a fine focus X-ray tube, electronic focus 8mm x 0.4mm configuration should be used. In the normal design a 6° take off angle is chosen, which leads to strong self absorption in the anode of the low energy X-ray photons. A compromise between high brilliance and low self absorption was made and a take off angle of 19 degree was chosen.
A commercially available high power diffraction tube was modified and integrated in the vacuum circuit of the measuring chamber. The anode was designed easily exchangable and Si was the target material. The anode geometry was optimized for high brilliance and low absorption.
An improvement of detection limits in comparison to a standard Cr anode fine focus tube could be obtained. Results are presented.