Public defense of doctoral thesis in electronics with Siwen An
Welcome to the defense of doctoral thesis in electronics with An Siwen. She will present her doctoral thesis: Spectroscopic and Microscopic X-ray Fluorescence Analysis for Environmental and Industrial Applications.
Join on site or online
You can choose to join the seminar on Campus Sundsvall in Room C312 or join online on Zoom. You can also watch Siwens presentation on Youtube on the link above.
Meeting ID: 670 3438 5235
Passcode: 272489
Respondent: Siwen An
Supervisor: Associate Prof. Börje Norlin, Mid Sweden Univeristy
Co-supervisor: Associate Prof. Göran Thungström, Mid Sweden Univeristy and Dr. David Krapohl
Opponent: Professor Yuying Huang, Shanghai Institute of Applied Physics
Chaiman: Associate Prof. Benny Thörnberg, Mid Sweden University
Grading committee:
Professor Richard Brenner, Uppsala Universitet
Professor Anders Hallén, Kungliga Tekniska Högskolan
Dr. Gabriella Josefsson, Hamamatsu Photonics
Abstract
Heavy metals are well-known environmental pollutants due to its potential impact on associated ecosystems and human health. Thus, it is important to monitor the levels of heavy metals in the environment. X-ray fluorescence (XRF) analysis is a powerful and effective screening tool in measuring the concentration of multi-elements simultaneously.
This thesis provides insight into development and implementation of XRF instruments for environmental monitoring and industrial process control. The XRF method was compared with a commercial scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) for fly ash samples. Qualitative analysis and semi-quantitative analysis of Na, S, Cl, K and Cd in incineration fly ash were performed with these two similar techniques. One of the challenges of using XRF is the scattering background noise from the primary beam, which decreases the detection limit and the sensitivity of the measurement system. Hence, an X-ray beam filter was chosen to suppress the background noise for a specific element, Cr, in leachate. Numerical simulations and experiments were developed to find the proper filter material and thickness by calculating the X-ray fluorescence intensities and the signal-to-noise ratio. The developed system is capable of online monitoring of Cr levels, to certify that the concentration is below the threshold level in leachate. An XRF prototype was built and calibrated for underwater Hg analysis in maritime wet sediment using a radioisotope source. The presented results show that it is possible to detect Hg by K-shell emission thus enabling XRF analysis for sediment underwater.
For non-homogeneous samples, an image revealing the elemental distribution can be achieved by micro-XRF (µ-XRF). XRF mapping of element distributions on a microscopic level was obtained by using scanning XRF microscopy and full-field XRF projection microscopy (FF-XRF). The spatial resolution of the scanning XRF imaging setup using an X-ray tube is in the order of 100 µm, but need to be further improved to measure the homogeneity of S on individual fiber level in pulp and paper industry. For the scanning technique, it is a tradeoff between resolution and measurement time. Another technique is FF-XRF imaging, and a setup was implemented using an energy resolving pixel detector and X-ray optics. The capabilities and limitations of using X-ray optics in XRF imaging systems have been identified. These microscopy measurements can guide further comprehensive environmental and industrial monitoring missions, utilizing elemental distribution information.
