Towards Standardization of Digital Neutron Radiography and Tomography: Setup Characterization and Application in Porous Media Quantification

Digital thermal neutron imaging (radiography and tomography) is a powerful non-destructive analytical tool and has demonstrated its importance in industrial- and research application world-wide. The standardization process, to certify digital thermal neutron imaging as a standard practice in industry, entails standardized test phantoms to be evaluated. Through the evaluation of the phantoms the spatial resolution and contrast of a thermal neutron digital imaging system can be determined in a controlled and standardized manner by accepting good practice in terms of scanning, data processing, data visualization and evaluation. Standard test phantoms are objects with physical features designed to test facility capabilities to reveal these features without any ambiguity. The good practice enables the acceptable assessment of different international digital thermal neutron imaging facilities for spatial resolution and contrast abilities. The purpose of this contribution is to establish good practice for the experimental setup, acquiring of 2-D digital projections and the reconstruction processof the 3-D digital images of standard test phantoms for spatial resolution and contrast. Results obtained from applying this suggested good practice on the contrast standard test phantom will be discussed. Another challenge is that qualitative measurements using digital neutron imaging has been the more explored aspect than accurate quantitative measurements. The reason for this bias is that quantitative measurements require correction for background and material scatter, and neutron spectral effects. This work evaluates the capabilities of the QNI software package to produce accurate quantitative results on specific characteristics of porous media, and its role to non-destructive quantification of material with and without calibration. The work further complements QNI abilities by the use of different sample-detector distances (SDDs). Studies of the measurement of the effective percentage porosity of mortar samples using the calibrated attenuation coefficient of water, using QNI and the SDD principle, are reported. (author)