We want to know Compton scattering components of Co-57 spectrum. So we estimate back scatter components from adding Al Bar and a plastic souce package (Co57-121) by Geant4 simulation.
As following, we show the geometry in this simulaiton. An active souce and Al bar sit ~ 2 meters above a coded mask (Rad source Z=294.4 cm). (cal data: arr_x_co57_200_20_030619_2.fits) And there is Co-57 source within the plastic tablet.Also Al bar structure is like a tube, that design is based on Ann's pdf file of source holder configuration picture.
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We refered to this picture in this simulaiton, so a tablet diameter is 25.4 mm and a thickness is 6.35 mm. Then, there is a position of beam radiation in the center of the souce tablet. However, we don't have informaiton about this fiber reinforced plastic (FRP) for details. So the chemical composition of plastic is approximated by CH2, and the density is 1.5 g/cc in this simulation.
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We compare both spetra With/Without Al Bar. We want to see the scattering components, we scale up the green peak height. We can see, the backscatter component(~ 400 [CH]) is almost same. But generated photons in this simulaiton are about 5 times less than in last simulaiton, because there is not enough simulation time. Is this reason ?