培训课件X射线荧光分析导论.pptVIP

Polymer Detector Windows Optional thin polymer windows compared to a standard beryllium windows Affords 10x improvement in the MDL for sodium (Na) 当前第30页\共有66页\编于星期三\22点 Detector Filters Filters are positioned between the sample and detector in some EDXRF and NDXRF systems to filter out unwanted x-ray peaks. Sample Detector X-Ray Source Detector Filter 当前第31页\共有66页\编于星期三\22点 Detector Filter Transmission % T R A N S M I T T E D ENERGY Low energy x-rays are absorbed EOI is transmitted Absorption Edge X-rays above the absorption edge energy are absorbed Very high energy x-rays are transmitted S Cl A niobium filter absorbs Cl and other higher energy source x-rays while letting S x-rays pass. A detector filter can significantly improve detection limits. Niobium Filter Transmission and Absorption 当前第32页\共有66页\编于星期三\22点 Filter Vs. No Filter Unfiltered Tube target, Cl, and Ar Interference Peak Detector filters can dramatically improve the element of interest intensity, while decreasing the background, but requires 4-10 times more source flux. They are best used with large area detectors that normally do not require much power. 当前第33页\共有66页\编于星期三\22点 Ross Vs. Hull Filters The previous slide was an example of the Hull or simple filter method. The Ross method illustrated here for Cl analysis uses intensities through two filters, one transmitting, one absorbing, and the difference is correlated to concentration. This is an NDXRF method since detector resolution is not important. 当前第34页\共有66页\编于星期三\22点 Wavelength Dispersive XRF Wavelength Dispersive XRF relies on a diffractive device such as crystal or multilayer to isolate a peak, since the diffracted wavelength is much more intense than other wavelengths that scatter of the device. Sample Detector X-Ray Source Diffraction Device Collimators 当前第35页\共有66页\编于星期三\22点 Diffraction The two most common diffraction devices used in WDX instruments are the crystal and multilayer. Both work according to the fo