| Fast neutrons with high energy,strong penetration and other advantages.Fast neutron radiography can enable neutron imaging testing of thicker samples,and has wider application value.The development of miniaturized mobile fast neutron camera system with compact neutron generator is an important development direction.The BSA design is one of the key issues to be studied.Based on the compact D-D / D-T neutron generator,the simulation and design of the beam-shaping-assembly for DT and DD fast neutron radiography are carried out respectively.According to the energy spectrum and angular distribution data of D-D / D-T reactive neutrons and the structure and materials of the compact neutron generator,the MCNP simulation model was established.A simulation study of the n /? radiation field of a compact D-D / D-T neutron generator is carried out.The results show that the neutron emission,scattering and absorption of the neutron generator have a significant effect on the n/ ? radiation field.The neutron generator neutron output window has the least effect,and the neutron flux highest,neutron monotonicity is best.The physical design of the fast neutron rediography beam-shaping-assembly based on the compact D-T reaction neutron generator was completed by the neutron / gamma transport simulation using the MCNP program.The outer dimensions of the rectangular parallelepiped composite shield are: 248cm(long)×178cm(width)×178cm(height),35cm-Fe + 35cm-PE(with8% B)+ 4cm-Pb.The simulation study of neutron beam characteristic parameters was carried out.In the sample plane on the diameter of 18 cm irradiation field,the relative neutron beam of the collimated neutron beam is about 5.24×10-6 cm-2(relative to the unit neutron),the fast neutrons with energy greater than 10 MeV are about 88.17%.Neutron fluence rate of non-uniformity is about 5.40%,to meet the fast neutron rapid photography on the basic requirements of the volume rate.Collimated neutron beam has good parallelism.The physical design of the fast neutron rediography beam-shaping-assembly based on thecompact D-D reaction neutron generator was completed by the neutron / gamma transport simulation using the MCNP program.Rectangular composite shield external dimensions: length164cm×width 96cm×height 83cm;30cm-PE(with 8% 10B)+3 cm-Pb.The simulation study of neutron beam characteristic parameters is carried out.The neutron fluence of the plane collimated neutron beam relative to the source neutron is about 2.42×10-5 cm-2,and the neutron and ?fluence ratio is about 8.In the range of diameter ?6cm irradiation field,the neutron fluence of the collimated neutron beam is about 6.55%,which satisfies the basic requirement that the neutron fluence of the neutron image is not more than 8%,and the collimated neutron beam mainly for fast neutrons with energy greater than 2MeVThe.collimated neutron beam has a good parallelism.A simulation study was conducted on the radiation dose of D-D / D-T neutron generator collimated shield.The results show that the distance between the D-T neutron generator collimated the shield one meter away from the collimated neutron exit surface,the average dose rate of neutrons spot region was 2.03×104?Sv / h,and the average dose rate of neutrons in other regions was 97.86?Sv / h,that is,the need to increase the thickness of the shield.The average dose rate of neutrons in the beam spot of the D-D neutron generator shielding was 263.62?Sv / h,and the average dose rate of neutrons in other regions was 7.96?Sv / h.The overall shielding effect of the shield was better.The amount of?dose equivalent in the shield is three levels lower than that of neutrons,and is within the safe range specified in the radiation protection standard. |
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