A conceptual design of neutron collimator in the thermal column of Kartini research reactor for in vitro and in vivo test of Boron neutron capture therapy

Studies were carried out to design a collimator which results in epithermal neutron beam for in vitro and in vivo of Boron Neutron Capture Therapy (BNCT) at the Kartini research reactor by means of Monte Carlo N-Particle (MCNP) codes. Reactor within 100 kW of thermal power was used as the neutron source. The design criteria were based on recommendation from the International Atomic Energy Agency (IAEA). All materials used were varied in size, according to the value of mean free path for each material. MCNP simulations indicated that by using 5 cm thick of Ni as collimator wall, 60 cm thick of Al as moderator, 15 cm thick of ⁶⁰Ni as filter, 2 cm thick of Bi as γ-ray shielding, 3 cm thick of ⁶Li₂CO₃-polyethylene as beam delimiter, with 1 to 5 cm varied aperture size, epithermal neutron beam with maximum flux of 7.65 x 108 n.cm^-2.s^-1 could be produced. The beam has minimum fast neutron and γ-ray components of, respectively, 1.76 x 10^-13 Gy.cm².n^-1 and 1.32 x 10^-13 Gy.cm².n^-1, minimum thermal neutron per epithermal neutron ratio of 0.008, and maximum directionality of 0.73. It did not fully pass the IAEA's criteria, since the epithermal neutron flux was below the recommended value, 1.0 x 10⁹ n.cm^-2.s^-1. Nonetheless, it was still usable with epithermal neutron flux exceeding 5.0 x 10⁸ n.cm^-2.s^-1. When it was assumed that the graphite inside the thermal column was not discharged but only the part which was going to be replaced by the collimator, the performance of the collimator became better within the positive effect from the surrounding graphite that the beam resulted passed all criteria with epithermal neutron flux up to 1.68 x 10⁹ n.cm^-2.s^-1. (author)