Application of Factorisation Methods to Analysis of Elemental Distribution Maps Acquired with a Full-Field XRF Imaging Spectrometer

Bartłomiej Łach,Paulina Krupska-Wolas,Stefan Koperny,Krzysztof Świentek,Bartosz Mindur,Tomasz Fiutowski,Paweł M Wróbel,Władysław Dąbrowski,Agata Mendys-Frodyma,Marek Lankosz,Piotr Wiącek

doi:10.3390/s21237965

Bartłomiej Łach, Paulina Krupska-Wolas + Show 9 more

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https://doi.org/10.3390/s21237965

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Abstract

The goal of the work was to investigate the possible application of factor analysis methods for processing X-ray Fluorescence (XRF) data acquired with a full-field XRF spectrometer employing a position-sensitive and energy-dispersive Gas Electron Multiplier (GEM) detector, which provides only limited energy resolution at a level of 18% Full Width at Half Maximum (FWHM) at 5.9 keV. In this article, we present the design and performance of the full-field imaging spectrometer and the results of case studies performed using the developed instrument. The XRF imaging data collected for two historical paintings are presented along with the procedures applied to data calibration and analysis. The maps of elemental distributions were built using three different analysis methods: Region of Interest (ROI), Non-Negative Matrix Factorisation (NMF), and Principal Component Analysis (PCA). The results obtained for these paintings show that the factor analysis methods NMF and PCA provide significant enhancement of selectivity of the elemental analysis in case of limited energy resolution of the spectrometer.

Highlights

The X-ray Fluorescence (XRF) spectroscopy is a well-established technique used for the investigation of the elemental composition of various materials including geological and biological samples as well as various types of artworks
An Region of Interest (ROI) corresponding to the mercury characteristic line of 10 keV was added, no clear signature of such a signal is visible in the spectrum
In the presented case studies, we demonstrated that the factor analysis methods Negative Matrix Factorisation (NMF) and Principal Component Analysis (PCA) are very effective tools for analysis and interpretation of the XRF images acquired with a full-field imaging spectrometer at limited energy resolution

Summary

Introduction

The X-ray Fluorescence (XRF) spectroscopy is a well-established technique used for the investigation of the elemental composition of various materials including geological and biological samples as well as various types of artworks. The macro-XRF technique utilises a focused X-ray microbeam for excitation of fluorescence radiation, a mechanical scanning system, and a high energy resolution X-ray detector, typically a silicon drift detector. When applied to the investigation of large area painting, it becomes quite time consuming, much progress has been made recently in various aspects of this method, including X-ray tubes, radiation detectors, mechanical scanning systems, and software. It is worth noting that the instrument has been developed addressing specific requirements of cultural heritage studies. It uses a stateof-the-art silicon drift X-ray detector providing the energy resolution at the level of about 2.5% Full Width at Half Maximum (FWHM) at 5.9 keV. The spatial resolution gets degraded if the investigated surface is not precisely in the focal plane of the microbeam [18,19]

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