Study On Neutron Spectrometry Measurement Method Based On The PGNAA Technology

Neutron spectrometry measurement is an important research content in neutron physics.It has important significance and research value in many application fields such as reactor design,neutron cancer treatment and neutron radiation protection.And it has always been a hot topic in frontier research.A new approach based on Prompt Gamma-ray Neutron Activation Analysis(PGNAA)was proposed for measuring neutron energy spectra in this research.When incident neutrons interact with the ?sample‘,whose composition of elements is known,the prompt gamma-rays are emitted from capture reaction(n,?)and inelastic scattering reaction(n,n? ?).These gamma-rays can be recorded by a detector and the counts of each characteristic peaks related to the energy spectrum of incident neutrons.First of all,the theory and the implementation process of this method was described and the feasibitity was discussed in this paper;According to this theory,the measurement system based on HPGe detector was designed and built.The system consisted of a high purity germanium(HPGe)detector,a multi-layer sample and the detector shield.The measurement system was designed and optimized by Monte Carlo simulation and unfolding simulation process.The multilayer sample was designed to a cube with an edge length of 10 cm,and the materials were 1 cm thick lead,1 cm thick acrylic,1 cm thick Na Cl powder,6 cm thick acrylic and 1 cm thick borated polyethylene(BPE).The shield structure included polyethylene block and lithium carbonate powder as neutron shield and bismuth as gamma-rays shield.And the response function of this system was obtained through Monte Carlo simulations.Later,the neutron fields of D-T neutron generator,Cf-252 neutron source,and PE-moderated Cf-252 neutron source were investigated with this system.With the gamma spectra(sample and background)measured in the experiments,the counts of these characteristic peaks in different neutron fields were obtained by 'Gamma Fit'.Based on the counts of these characteristic peaks and the response function,the unfolding was carried out by the PSO algorithm.The unfolded spectra had good agreement with the simulation spectra overall,the feasibility and accuracy of this method was demonstrated from the unfolded results,experimentally.