Micro Xrf of Light Elements Using a Polycapillary Lens and an Ultra Thin Window Silicon Drift Detector inside a Vacuum Chamber

Since most micro-spectrometers are operated in air, up to now only mapping of medium and higher Z elements was possible with micro X-ray fluorescence analysis (μ-XRF). Though for some applications (e.g.: biologicaland geological samples, samples from art and archeology) the extension to light elements is of great interest. Therefore μ-XRF measurements using a polycapillary lens mounted inside a vacuum chamber have been performed. X-rays from a 2kW high power diffraction tubes (Mo and Cr anode) as well as from a low power 50 W Pd-anode tube were focused by means of the polycapillary X-ray optics. The polycapillary adjustment was performed with a combination of an X/Y stage and a gimbal allowing 3 translation and 2 rotation movements. With this setup it was possible to produce an X-ray spot of about 40μm in diameter at the sample surface. Sample motion is performed by an x-y-z-micrometer driven stage PC controlled. The position dependent fluorescence signal was collected by a Peltier cooled energy dispersive detector (10 mm2 Silicon Drift type) with an ultrathin window (300nm) allowing the detection down to oxygen. Scanning measurements have been carried out on various samples of human femural bone. Results from an area scan (500 x 1100 μm) across the transition zone of trabecularand cortical bone are presented, including the distribution of O, P, Ca, and Zn. To compare the performance of the different anode X-ray tubes single point measurements on NIST glass (soda lime glass) have been performed with regard to light element detection. A comparison of results using the different excitation conditions of Mo-L and Pd-L on various samples will be presented with excellent conditions regarding excitation, detection, and background using a vacuum chamber for μ-XRF.