Development Of A Time Projection Chamber(TPC) For High Precision Fission Cross-section Measurements

Nuclear fission has been widely used in the fields of nuclear reactors,nuclear weapons,nuclide synthesis and astrophysics.In these fields,the nuclear data of fast neutron regions are very sensitive,and the demand for precision of the fission cross section is very high.For example,in the design of the reactor system,the system is often evaluated by the high precision simulation software because of the feasibility and cost of measurement.The accuracy of nuclear data has great influence on the simulation results.The influence of the fission cross section uncertainty on these fields has been studied in detail.The results show that the uncertainty of fisson cross section needs to reach 1%or less.At present,for the main fission nuclides such as ²³⁵U and ²³⁸U,the accuracy of the reaction section is 3%-5%,and the accuracy in the fast neutron region is even worse.The traditional measurement method has reached the limit and a new measurement method is needed.To achieve this goal,a Time Projection Chamber for high precision fission cross-section measurements is studied in this thesis.Simulation study,parameter optimization,set-up and performance test are completed for the fission TPC.The specific research contents include:?1?A simulation platform was carried out.In the simulation,the ionization process of the particle was simulated using Geant4.Based on fast MC algorithm,the drift and multiplication process of electrons was simulated uing ROOT.Garfield was used to get the parameters of electrons in the gas.SRIM was used to simulate the particle range.The parameters of the system was optimized according to the simulation results;?2?The TPC system was constructed and tested.The results showed that the system works normally,providing conditions for the performance test of the system;?3?The ability of particle differentiation was tested by using a ²⁵²Cf source.The data processing flatform was builded and the construction of the platform included the method of particle tracking and the removal of the background signals.According to the test results,the cross section uncertainty introduced by the particle differentiation was calculated to be less than 1%,which maked the cross section precision less than 1%possible.?4?The impact of target non uniformity to the cross section uncertainty was analysised and the resolution of the track starting point was proposed to reach 1mm.The following test showed that the TPC could meet the requirements;?5?The neural network was proposed to improve the particle differentiation ability.Through the test,the cross section uncertainty introduced by the particle differentiation could be further reduced.When the neutron flux was 10⁸n/s.cm and the thick of the²³⁵U target was from100ug/cm2to 500ug/cm2,the uncertainty was reduced by 3 to 5 times compared with the traditional method.?6?The other uncertainty sources of the system were analysised and the cross section uncertainty measured by TPC was reduced to 0.93%,indicating that the cross section accuracy is likely to meet the requirements of 1%.The performance could meet the accuracy requirements.