A STUDY OF MULTIPLE-SCATTERING BACKGROUND IN COMPTON SCATTER IMAGING

The multiple scattering background in Compton scatter imaging at 662 k eV is studied, both experimentally and by Monte Carlo radiation transp ort calculations, as a function of the scattering angle, scattering ma terial (aluminium, brass and tin) and object thickness. A double-peak structure was observed in the pulse-height distribution for the thicke r brass and tin objects and at the larger scattering angles (90 degree s and 120 degrees). In addition to the Compton peak, a second peak app eared at a higher energy. Monte Carlo transport simulations have revea led the origin of the second peak: photons that have scattered exactly twice before reaching the detector. The ratio of the multiple-scatter ed radiation to the total radiation detected was calculated as a funct ion of the energy-window width around the Compton peak and scattering angle. The results of this study may help in the design of future Comp ton scatter imaging apparatus.