A STUDY OF MULTIPLE-SCATTERING BACKGROUND IN COMPTON SCATTER IMAGING

The multiple scattering background in Compton scatter imaging at 662 keV is studied, both experimentally and by Monte Carlo radiation transport calculations, as a function of the scattering angle, scattering material (aluminium, brass and tin) and object thickness. A double-peak structure was observed in the pulse-height distribution for the thicker brass and tin objects and at the larger scattering angles (90 degrees and 120 degrees). In addition to the Compton peak, a second peak appeared at a higher energy. Monte Carlo transport simulations have revealed the origin of the second peak: photons that have scattered exactly twice before reaching the detector. The ratio of the multiple-scattered radiation to the total radiation detected was calculated as a function of the energy-window width around the Compton peak and scattering angle. The results of this study may help in the design of future Compton scatter imaging apparatus.