Study On Unfolding Of Neutron Energy Spectrum Technique Based On Triple GEM New Fast Neutron Detector

This job has completed related work about unfolding of neutron energy spectrum by the new fast neutron detector which is based on Triple GEM,including researching references,writing simulation programs,building unfolding programs and participation in the construction of experimental platforms.The obtained results show that performances of unfolding programs in the new neutron detector are well.Detail information and results of this work are summarized into the following Three sections:Firstly,high density polyethylene film(HDPE)as a neutron conversion material of new neutron detector based on Triple GEM is used,its rationality and performance are fully simulated by the software of Geant4 and ROOT.According to the results come from simulating D-D,D-T and Am-Be fast neutron sources,the value of the neutron conversion efficiency reaches the maximum value around 0.07%,0.37% and 0.12% when the thickness of single layer HDPE is 0.8mm,2mm and 1.2mm,respectively.In addition,thickness mentioned above coupled with the gas interval of 500?m is consider as a unit.The results confirm that the neutron conversion efficiency of multi-layer HDPE is about one order of magnitude higher than that of single-layer.Therefore,detection efficiency can be increased effectively by multi-layer HDPE.Secondly,optimizing conversion structure of new detector.In fact,neutrons will loss some energy due to elastic scattering with polyethylene,in order to improve neutron conversion efficiency further,this work uses the method of decreasing the thickness of polyethylene to increase the probability that the recoil proton will escape the conversion layer.Thirdly,writing unfolding programs by MATLAB,which is based on GRAVEL algorithm,maximum likelihood algorithm,improved maximum likelihood algorithm,least squares method and genetic algorithm.Unfolding results of mono-energy(2MeV,4MeV,8MeV,12 MeV,14MeV)and continuous-energy(Am-Be)neutron sources represent that the above five algorithms are applicable to the new fast neutron detector based on Triple GEM.The mono-energy neutron spectrum has good spectral resolution,accurate peak position and small broadening.For Am-Be neutron source,the genetic algorithm has outstanding performance and obvious advantages.