Basic design analysis of PGNAA system using neutron source from beamport of Kartini reactor

A preliminary design analysis of PGNAA system using one of reactor beamports of Kartini reactor as a neutron source have been carried out. Neutron moderator is placed at the inner end of beamport column to make thermal neutron beam. A neutron beam directed to PGNAA counting chamber by using collimator as a filter to make parallel neutron beam. At the middle of collimator intersect with beamport window, neutron beam shutter is mounted to close when not in use for PGNAA. Beam stopper mounted behind the sample chamber of PGNAA to capture neutron beam that passes from the sample chamber. Calculation of neutronic properties of materials was done to choose the material that meet the functional requirements of PGNAA and to determine the geometry size. Based on the calculational results obtained that good material for moderator is graphite, aluminum as beam collimator, and beam shutter or stopper is made from borax-paraffin composite. The moderator length is 90 cm and collimator length is 173 cm with collimation constant D/L = 0,015. Beam shutter and beam stopper thickness are 22 cm and 30 cm respectively. Gamma and neutron shield are added surrounding beam collimator to shield the radiation out from the pitch between collimator and beamport wall. The shield material made from composite of parrafin 25 w % borax, and lead with the length of 50 cm and 30 cm respectively. The analysis result shows that from the neutron flux of 1,5.10¹² n/cm²s at the inner side of beamport, can generate thermal neutron flux at the PGNAA sample chamber of 1,76.10⁸ n/cm²s with the thermal neutron current of 9,29.10⁸ n/s. This thermal neutron flux meet the requirement for a PGNAA system i.e. in the order of 10⁶ to 10⁸ n/cm²s. (author)