AmBe Neutron Source Polyethylene Leak Neutron Energy Spectrum Measurement Technology Research

In the project of the international thermonuclear fusion reactor,the radiation protection of D-T neutron and the performance validation of shielding material are essential part of the research work,in which including the measurement of D-T leakage neutron spectrum through the medium.The range of D-T leakage neutron spectrum through the medium is rather wide,which mainly concentrated in the medium and low energy area.In the circumstances of not being able to build the time of flight(TOF)neutron spectrometer detection system,it is particularly important to establish an effective and simple detection system for the measurement of a wide dynamic range of neutron energy spectrum.Measurement technique of neutron energy spectrum is studied based on the recoiled proton method and the organic liquid scintillation detectors.The measurement technique base on above method includes four aspects:n—?discrimination,measurement of the recoiled proton spectrum,simulation of the response functions and the unfolding.Predecessors had done a lot of work about the first two experimental technologies,this work focus on the simulation of response functions and unfolding.Using Geant4 to simulate the response function of the 14.88 MeV D-T neutron in the organic liquid scintillation detector,and investigated the reaction channels calculated by the "QGSP_BIC_HP" physical model,simulation result shows good accordance with the nuclear database.Besides,the above simulated response function was compared with an experiment data,the result also shows good agreement,which also indirectly proved the validation of the program in simulating the neutron response in a wide energy range.Then according to the mathematics and related physical meanings,elaborated and studied the influence of different energy intervals and channel width on the unfolding results.Results showing that better unfolding performance can be obtained when the response function interval basically equals to the least energy resolution of the detector system and the channel width is in the order of 1/3?1/2 of the energy interval.Based on the above simulation results,the detector response functions in the energy range from 0 to 11 MeV with an energy interval of 0.25 MeV and a channel width of 0.08 MeVee are generated.In order to verify the reliability and the layouts of the response matrix for the medium and low energy range of the D-T neutron through the medium,the measurement of the recoiled proton spectrum for the AmBe neutron source was performed.The n—? discrimination was realized using zero-crossing method.The experimental measurement scheme was determined by using MCNP5 to simulate the scattering neutrons.According to the problem about how to obtain the neutron energy spectrum from the recoiled proton spectrum,the bayes probability method,singular value decomposition method and the regularization method were investigated.Using above algorithms to unfold the measured spectrum to obtain the neutron energy spectrum for AmBe neutron source.These results basically accord with the reference distribution well.The result obtained by Bayes method perform the best smoothness feature among them,however,the distinction on the whole spectrum is less satisfactory.The result based on SVD method has the most reduction degree over the medium and high energy range,however,the result in low energy area is not ideal.The result based on the regularization method has a comprehensive performance in this condition.To verify the applicability of this method on the energy spectrum measurement of the leakage D-T neutron through the medium.Using polyethylene to slow the AmBe neutron,and then measured the leakage neutron energy spectrum with the same experiment method.Identically,three unfolding methods were applied on the measured leakage neutron energy spectrum.The results basically accord with the reference distribution well.