Trace Analysis of a Beryllium Window for a Solid State Detector System by Inductively Coupled Plasma Mass Spectrometry

Transition metallic impurities in high-purity Be for a window of the solid state detector (SSD) of a commercially available total-reflection X-ray fluorescence (TXRF) analyzer were determined by the use of ICP-MS analysis. From this analysis, 150μg/g of Fe and 100μg/g of Ni were detected. Other impurities were less than 55μg/g. In the determination of trace metallic impurities (of the order of 1010 atoms/cm2) on Si wafer surfaces by TXRF, X-ray fluorescence, such as Fe Kα and Ni Kα, are known to be observed, even if these elements do not actually exist on the surface. These spurious peaks appear when the primary beam of W Lβ radiation satisfies the Bragg condition and the diffracted beam is detected by SSD. From our investigation, impurities in Be were found to be one of the origins of this phenomenon, because the diffracted W Lβ radiation which is impinged into the SSD through the Be window excites the impurity in the window.