| Popis: |
The neutron generators supporting to the clinical trials are usually the fission research reactors1,2 and the high-current proton accelerators.3,4 In both case, special systems of moderator, collimators, filters and shielding are optimally assembled in order to match the requirements of the BNCT treatment. Those requirements are the high intensity of the epithermal neutron component, the low level of contamination, and the radiation shielding criteria. However, it is not always possible to fulfill all engineering and physical requirements due to the adaptation of a beam port of a nuclear research reactor to accomplish a medical facility. It has often required large changes in the reactor core and in the configuration of the structural building, investing the high cost. This paper addresses about an intermediary alternative, cheap and simple, irradiation facility that is able to deliver a good quality epithermal neutron beam with low background of fast neutrons and gamma rays. Herein, a conceptual design is presented and neutronic simulations are carried out. The proposed facility is composed of a set of 252Cf sources coupled with special systems of moderator, collimators, filters and shielding. A geometric and material-choice optimization is made in order to maximize the epithermal neutron flux and minimize the fast neutron and gamma ray doses in the irradiation port. Monte Carlo N-Particle transport code—MCNP7 is used to estimate and optimize the main geometrical and material-choice parameters of the moderators, collimators, filters and shielding systems. The irradiation port is able to deliver an epithermal neutron flux at in the range of 4eV up to 40keV in a forward directional neutron current. In order to increase the intensity of the epithermal neutron flux in the beam port, a configuration loaded with 252Cf-235U is proposed in a subcritical neutronic fashion. |
