Tube defects inspection technique by using Compton gamma-rays backscattering

In this work the Compton scattering technique is used to detect superficial defects in tubular shaped objects. The study was performed using a system with a 137Cs source, with an activity of 74 GBq (2 Ci) and a 50.4 mm×50.4 mm NaI(Tl) cylindrical detector placed in such a way that it was possible to obtain scattering angles of around 180°. In the first part of the work, we use the pulse-height spectrum of scattered radiation to analyze the thickness of known test objects. With the energy callibration obtained, it was possible to determine the thickness with a precision of 4% for test objects within the calibration limits, and 6% for values beyond these limits. In the second part, we used the calibration to analyze surface defects. It was possible to detect 2 mm corrosion in a 77.3 mm tube diameter with a 6.3 mm thickness wall for corrosion in the first tube wall, with the tube positioned at 5.0 mm from the detector.