Optimization of neutron spectrum in northwest beam tube of Tehran research reactor for BNCT, by MCNP code

In order to gain the neutron spectrum with proper components specification for BNCT¡ it is necessary to design a Beam Shape Assembling (BSA)¡ including moderator¡ collimator¡ reflector¡ gamma filter and thermal neutrons filter¡ in front of the initial radiation beam from the source. According to the result of MCNP4Csimulation¡ the Northwest beam tube has the most optimized neutron flux between three north beam tubes of Tehran Research Reactor (TRR). So¡ it has been chosen for this purpose. Simulation of the BSA was done in four above mentioned phases. In each stage¡ ten best configurations of materials with different length and width were selected as the candidates for the next stage. The last BSA configuration includes: 78 centimeters of air as an empty space¡ 40 centimeters of Iron plus 52 centimeters of heave-water as moderator¡ 30 centimeters of water or 90 centimeters of Aluminum-Oxide as a reflector¡ 1 millimeters of lithium (Li) as thermal neutrons filter and finally 3 millimeters of Bismuth (Bi) as a filter of gamma radiation. The result of Calculations shows that best neutron flux and spectrum will be achieved for BNCT by using this BSA configuration for TRR Northwest beam tube.