The experimental study of interaction of U-235 fission fragments with polymeric films

The main purpose of this work was the experimental study of U-235 fission fragment ranges in thin polymeric films and their comparison with calculated models according to the available theories. Moreover, the method of registration of charged particles in thin polymeric films may have perspective applications in experimental nuclear physics. We measured the U-235 fission fragment ranges in PET using the gamma-spectrometer. These experiments yielded data on ranges and distributions in the film depth for a large variety of fission fragments (we have investigated 18 fission fragments). The obtained data are compared with the available data for mylar film and the differences observed amounted to maximum 15 %. The comparison with the theoretically calculated data shows that the experimental data are lower by 20 % than the calculated ones. The distribution function of the track length averaged over all fission fragments was obtained by statistical methods using computer simulation. In the next step, fission fragments tracks in polymer films were investigated. Polyethylene terephthalate (PET) irradiation by U235 fission fragments was carried out in the BR-10 nuclear reactor (Institute of Physics and Power Engineering, Obninsk). A set of 15 thin (2.5 μm) closely packed PET foils was used. Investigation of foils from the irradiated 'set' allowed studying the structure of defects and the etching rate along the track. The surface density of defects corresponded to the calculated irradiation fluence. The foils from the first ('highest' in the set) to the 7th foil were tested with AFM (Institute of Crystallography, Moscow) and a steady decrease of the defect size was observed. AFM study of these films also demonstrated two types of radiation defects probably corresponding to two types of unequal fission fragments (mean mild and mean high). The experimental results show that the track has a cone form. The obtained results can be used for manufacturing reactor track membranes