The X-ray microbeam spectrometer of the LNS-Catania

An X-ray microbeam spectrometer has been installed at "Laboratorio Nazionale del Sud" INFN- Catania. It consists basically of an X-ray tube, a glass capillary (XCO) and a Si(Li) detector with its associated electronics. A conventional X-ray tube with W anode was used as X-ray source and a straight shaped capillary as focusing device. The detector was a Si(Li) with energy resolution of 170 eV at 5.9 KeV. To acquire and store the spectra the portable NOMAD PLUS MCA connected with a PC has been used. The spectrometer was also equipped with a standard microscope for positioning the beam on the samples during measurements. The incident angle and the take off angle are both of 45 degrees. As its well known the capillary works trough repeated total reflections at inner walls [1]. Total reflection occurs only for incident angle below critical angle that depends by 1/E. Thus X photons with different energies are transmitted with different efficiency. In particular a high energy cut off is present [2]. To use the X-ray microbeam for absolute determinations of element concentrations of samples, the incident capillary spectrum has to be determined. This has been carried on by performing scattering measurements on the polyethylene sample. Through calculations of Compton and Elastic cross sections in the polyethylene sample the incident photons flow has been determined. The X-ray microbeam was used in a mineralogical application. We have performed a quantitative analysis on a single olivine mineral whose major and trace elements were been previously determined trough electron microprobe and proton microprobe (micropixe). The quantitative analysis has been performed using the IEAEA QXAS 3.51 code in the option of Fundamental Parameters.