Neutron flux and gama dose profile measurements and calculations along a phantom in the BNCT facility of IEA-R1 reactor

Abstract

A BNCT (Boron Neutron Capture Therapy) facility has been built at IEA-R1 reactor. The on going BNCT experiments demand the maximization of the thermal neutron component of the irradiation fi eld and the minimization of its epithermal and fast neutron components together with the reduction of the gamma contamination. This work was developed with the objective of evaluating whether the present radiation fi eld in the facility is suitable for carrying on BNCT studies and to establish a work methodology with phantoms in this facility. In order to achieve these objectives, thermal and epithermal neutron fl ux measurements, in the sample irradiation position were performed using hyper-pure Gold activation detectors and applying the Cadmium ratio. Absorbed dose due to gamma radiation was determined by TLD 400. A cylindrical phantom composed by acrylic discs was designed, built and tested in the facility. DOT 3.5 computational code was used to retrieve neutron fl uxes and the gamma dose estimates along the phantom. Although some improvements still need to be made in the methodology under implementation, computer simulations carried out with DOT code presented a good agreement with experimental data for most part of the evaluated profi le. In the position corresponding to about half the length of the phantom, the following experimental values were obtained: thermal neutron fl ux (2.52 ± 0.06)·108 n.cm-2.s-1, epithermal neutron fl ux (6.2 ± 0.3)·106 n.cm-2.s-1, absorbed dose due to thermal neutrons (4.2 ± 1.8) Gy and (10.1 ± 1.3) Gy due to gamma radiation. The obtained values show that the fl uxes of thermal and epithermal neutrons fl ux are appropriate for studies in BNCT, however, dose due to gamma radiation is high, indicating that the facility should be improved.