A Parabolic Collimator as a Possible Solution in the TAPIRO Epithermal Column used for Patient Treatment with BNCT

In the Italian multidisciplinary BNCT project sponsored by MIUR, a series of calculations have been carried out to evaluate the possibility to irradiate patients by means of the TAPIRO fast reactor and an epithermal column mounted on one side of the core. The overall layout of the system and the choice of the materials must be carefully studied to fulfil all the BNCT requirements.In this work a neutronic analysis concerning the possible geometrical shapes for the TAPIRO epithermal column has been carried out. It is shown that an near-optimal solution, in terms of flux level at the exit window and in-phantom dose profiles, is the parabolic shape. Even if, in the first instance, the parabolic choice seems to be an exotic solution, the results of Monte Carlo calculations show excellent column performances and a good quality of ali the reference parameters used by the BNCT community. Since this geometry could represent a problem in terms of feasibility of construction, in the second part of the report some calculations employing plane geometry to fit the parabolic profile have been performed. A good compromise between the quality of the results and the technical feasibility has been obtained.