Energy resolved X-ray imaging as a tool for characterization of paper coating quality

Energy resolved X-ray imaging can be used as a tool to analyze the variation in the chemical content of an object. In this work we have used energy resolved X-ray imaging to measure the variation in the chemical content of paper and paper coating. This is an important quality parameter for the paper industry. In order to separate the variation in coating thickness from the variation in paper thickness, energy resolution is used to separate the response of the coating from the response of the paper. The MEDIPIX2 single photon processing X-ray imaging system has been used in the measurements. The measurement results are compared to simulations. The influence of charge sharing is discussed and the effects have been studied by comparing results from detectors with 220×220 ¿m² pixels and detectors with 55×55 ¿m² pixels. There is a trade-off between good spatial resolution obtained with detectors with small pixels and good energy resolution obtained with detectors with large pixels. The requirements on image quality, to achieve the resolution of coating distribution relevant for the application, are discussed.