detecting air holes in a concrete structure using gamma-ray tomography technique

Tomography is a technique in order to display a representation of a cross-section through solid objects using x-rays, gamma rays or ultrasound waves. The purpose of this paper is to provide a non-invasive technique for creating a CT image and detecting air holes in a concrete structure using gamma-ray tomography technique.In this work, the concrete column with a cross-section of 40 cm × 40 cm and length of 3 meters has been considered as the desired structure. There are two air holes in the concrete column. Also, the isotope Cs-137 was regarded as a radioactive source. One NaI(Tl) scintillation detector was used to measure the rate of gamma-rays emitted by the radioactive source. This structure was simulated using MCNPX code. Then, the image of cross-section was reconstructed using the obtained data of MCNPX, MATLAB software, and the ART algorithm. In the ART method, it is assumed that the cross-section contains unknown pixels. A row matrix (1 × n) and a column matrix (n × 1), which are the sum of the row pixels and column pixels of the image are defined as input for ART algorithm. The output is a matrix (n × n) that matrix arrays (n × n) are cross-section image pixels. Therefore, using these arrays, the cross-sectional image is reconstructed. The reconstructed image showed the correct location of the air holes. According to the obtained results, the proposed gamma radiation tomography technique is an appropriate and non-invasive technique in order to cross-sectional analysis of concrete structures.