A geometry and collimation study of a Compton backscatter device for inclusions detection in materials

Full text: Compton backscattering of gamma rays is a nondestructive technique that can be used for material characterization and detection of defects and inclusions in materials. The methodology allows one-side inspection of large structures, is relatively inexpensive and can be portable. The concept is based on detection of backscattered radiation produced from a collimated beam aimed at the sample. The energy spectrum of backscattered photons can be used to determine local density perturbations. In this work we carried out a geometry and collimation study of the Compton backscatter device that consists of a Φ 2mm collimated 241Am (100mCi) gamma source and a high resolution CdTe semiconductor detector. Acrylic and plaster blocks with inclusions of materials with different densities were used as samples. Collimators in the detector with φ 7mm, φ 5mm, φ 3mm and φ 1.5mm were tested in two different scattering angles: 135 deg and 150 deg. The results showed that the backscatter geometry of 150 deg with the Φ 5mm collimator resulted in higher count rates in the intensity versus energy spectrum without loss of spatial resolution. The tests on plaster blocks with steel rods inclusions suggest that, for a low energy and activity gamma source, the effects of beam attenuation are more decisive to the scattered intensity than increasing of material density. With the density contrast analysis, size and deep of steel rods can be determined. (author)