Detailed Multiple Scattering Profile Evaluation in Collimated Photon Scattering Techniques

The spectra of gamma radiation, multiple-scattered by large volume samples, have been studied in different irradiation conditions and positions of the sensitive volume (SV) defined by the intersection of the incoming beam and the solid angle seen by a detector collimation. Monte Carlo simulations of up to third order scattering are performed on phantoms of small and large dimensions compared to the mean free path of the incoming photons. Qualitative and quantitative results are discussed in terms of both the equipment collimation and the peak integration limits of the recorded photon energy spectra. Experiments with 59.54 keV incident photons and water phantoms are reported in order to validate the simulation results. The experimental and simulated results clearly show that the non-linear dependence of the multiple-scattered fraction on the SV position inside the sample volume cannot be ignored in the assessment of Compton tomographic techniques.