Example of the output produced by XRF Spectrum

Example of the output produced by XRF Spectrum taken using Amptek XR-100 CR 25 mm 2 X 500µm X-Ray Detector (20µs shaping time) and Amptek MCA 8000 A Multichannel Analyzer

Limitations of XRF - can’t differentiate between different isotopes of the same element - can’t differentiate between ions of the same element in a different valence state • only capable of measuring elements from Beryllium to Uranium

Summary of XRF 1. Sample bombarded by external primary excitation. 2. The high energy of the gamma ray engenders the ejection of an electron from the innermost orbital (labeled K) of an atom. At this point the atom is rendered unstable. 3. As an electron from the orbital L or orbital M fills the vacancy in orbital K, the electrons give off a characteristic x ray. 4. Meanwhile a vacancy has occurred in orbital L or orbital M, and the electrons in orbital M or orbital N fill in the vacancy. Giving off another unique x ray.

Excitation and Emission Spectra of XRF

Light Source and Detector Used Light source is a gamma ray which causes ionization due to its high energy. There are several types of detectors � Si � Ge � PIN diode � Silicon Drift Detector

XRF in forensic labs � � � XRD and XRF are becoming more used as part of a routine analysis. Adding high resolution Computed Tomography scanning with XRD or XRF allows for the most reliable and non destructive analysis. -tomography-is the imaging by sections or sectioning through the use of wave energy.

Why Use XRF? � XRD and XRF techniques both provide date that is: � Speedy, accurate and give reproducible results � Simple � Non destructive in nature of measurement These techniques are used with various crime scene evidence such as: explosive or bullet reside, soil samples, paint chips, duct tape, drugs, and cosmetics

XRF Instrumentation � � � XRF spectrometer is an x-ray instrument used for routine, non destructive chemical analysis. Works on wavelength dispersive spectroscope principles, which is similar to electron microprobe. Easy to prep, and the stability allows for x-ray spectrometers to be a commonly used method for analysis of trace evidence.

XRD and XRF tomography 1) XRD bends magnet radiation, which is monochromated by way of a double multilayer monochromater (DMM) 2) Energy is selected (30 ke. V beam) � Focused on the paint multilayer fragment by using a single bounce capillary to a spot size of 15 µm. 3) An area detector (8µm pixel size) was placed behind the sample in order to get the 2 D diffraction pattern. 4) A silicon detector at 90° with respect to incoming beam, which produces a fluorescent spectra. XRF(element distribution in a cross section) XRD(cyrstallographic phase distribution)

Figure 2 Combined μ-XRF/XRD tomography on a layered paint fragment at a synchrotron microfocus beamline. For each translation–rotation step (xi , ωk ) an XRF spectrum and 2 DXRD pattern are produced. The corresponding radial scatter profile, obtained by azimuthal integration of the CCD-camera image, can be decomposed in several crystallographic phase contributions. The S-coefficients form the sinograms Sc(x, ω) from which distribution maps gc(x, y) are calculated.

XRD XRF Figure 3. MLEM reconstruction of Pawley scaling factors of titanium dioxide and barium sulfate from XRD data in the first column, along with their major elements, titanium and barium from XRF data in the second column, showing the presence of rutile in three paint layers and barite in two layers. Two trace elements, strontium and niobium, show less absorption because of their higher energetic emission lines. Sinogram dimensions are 1. 2 mm(15 -μm steps) by 180◦ (3◦ steps). Tomogram dimensions are 1. 2 × 1. 2 mm (15 × 15 μmsteps).

Sources De Nolf, W. , Janssens, K. (2009). Micro X-ray diffraction and fluorescence tomography for the study of multilayered automotive paints. Wiley Interscience. http: //serc. carleton. edu/research_education/geochemsheets/techniques/ XRF. html http: //www. panalytical. com/index. cfm? pid=130 http: //www. amptek. com/xrf. html http: //www. panalytical. com/index. cfm? pid=873&itemid=154&contentitemi d=46