Comparison of SiLi detector and silicon drift detector for the determination of low Z elements in total reflection X-ray fluorescence

Abstract

The new commercially available silicon drift detectors (SDD) offer several advantages for their use in total reflection x-ray fluorescence TXRF like small design, low weight, electrical cooling, therefore no liquid nitrogen consumption. High throughput and excellent energy resolution (140 eV at 5.9 keV) as well as short distance between Be-window and crystal are other features. As the SDD showed good performance for medium Z elements in TXRF, an extension to the detection of low Z elements emitting low energy K-shell fluorescence radiation was of interest. An SDD (10 mm 2) was especially adapted with a 300-nm ultrathin entrance window (AP 1.3™ from MOXTEK) instead of the standard 8 μm Be window. This detector was tested in the Atominstitut wafer TXRF spectrometer, which allows measurements under vacuum conditions. Monochromatic Cr-Kα radiation from a 1300 W Cr anode fine focus diffraction tube and a multilayer monochromator was the exciting radiation. The data from the SDD measurements were compared to data obtained with an ultrathin window SiLi detector (30 mm 2). Both detectors have been equipped with the same electron trap to prevent the photoelectrons from entering the detector, as the ultrathin window is not an electron barrier. The SDD limited the detectable element range to oxygen, with the SiLi, it was possible to detect carbon easily. The detection limits for oxygen were 36 ng for the SDD in comparison to 4 ng with the SiLi, for Na 0.77 ng and 0.57 ng were obtained, respectively, measured using the same sample. So it could be shown that the SDD offers excellent low energy performance down to oxygen.