Study On Moderating And Shielding System Of D-T Neutron Generator By Using Monte Carlo Simulation

Neutron activation analysis is a kind of fast and non-destructive detection method,which can be used for qualitative and quantitative analysis of measured substances through the energy and counting of gamma rays generated by the interaction between neutrons and sample.The method has been applied in the fields of coal quality analysis,explosive detection and neutron therapy,et al.The model NG-9 D-T neutron generator developed by Northeast Normal University is a small accelerator neutron source,which has the ability of producing fast neutrons with 14 Me V energy in a maximum yield of 4 × 108 n/s.Based on the materials and specifications of the NG-9 neutron emitter,we designed the shielding structure and thermalization structure of the neutron emitter through MCNP simulation,which has reference for the application of neutron sources.Shielding around the neutron generator is necessary to protect the operators from radiation exposure from neutron and gamma rays during operation.In this study,the MCNP5 code was used to construct a generic building with an activation room and corresponding six surrounding rooms.In the activation room,the shielding structure around the neutron emitter was designed,and a cavity was reserved for the neutron activation analysis experiment.Several designs of shielding structure were evaluated to ensure that the total dose rates for neutrons and photons in surrounding rooms are in the limit of acceptable dose.The results show that the annual operation time can reach to at least 4056 hours for operators with the optimized design.Due to the 14 MeV neutrons generated by Deuterium-Tritium(D-T)fusion reaction usually need to be moderated for thermal neutron activation analysis experiments,a fast neutron beam thermalization device was developed in Northeast Normal University based on the D-T neutron generator(model NG-9).A simple experimental system was set up firstly to validate the feasibility of simulation.The materials and dimensions of moderator and the size of multiplier,reflector and collimator were then optimized through MCNP5 to improve the efficiency of the thermalization device.The results show that the thermal,epithermal,fast and total neutron flux across the output surface in final system are increased for a factor of 9.65,8.70,5.84 and 6.94 times compared to the initial experimental system,respectively.And the optimized thermalization efficiency is 13.28 times higher than that of the original model of experimental system.