The role of multiple scattering in the image formation with a gamma Compton backscattering device
C. M. Garzón Flórez 1*, F. Cristancho 2,3
1 Universidad Industrial de Santander, Bucaramanga, Santander.
2 Centro Internacional de Física, Bogotá, Colombia.
3 Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia.
A successful gamma-backscattering imaging device has been designed and shown to be able of producing images of photographic quality. The apparatus uses the positronic decay of 22Na that produces two 511 keV gamma-rays travelling in opposite direction. If one of the photons flies towards a conveniently placed position-sensitive detector, the other one will travel towards the inspected sample. Collection in the PD is triggered if the second photon backscatters in the sample and hits a second, called backscattering detector (BD). According to this schematic operation principle, the gamma-ray interacting with the sample may do one or more Compton scatterings before being registered by the BD. This, in turn implies that triggering data collection in the PD can be done by the first, the second and so on, Compton-scattered gamma-rays. There is then the question whether the multiple Compton scattering has a constructive or detrimental role on the image formation. The present work uses Geant4 to simulate the whole process, positronic decay, gamma interaction with both sample and instrument to determine the contribution of single-, in comparison to multiple-Compton scattering and their role in the formation of the image.