Study On A New Neutron Flux Measurement Method For Fast Neutron

In recent years,with neutron widely used in materials,biology and nuclear physics field,researchers payed more and more attention to it.Therefore,neutron detection has become a research hotspot.The ~3He proportional counter and scintillator detector are commonly used for detecting neutron,however,~3He proportional counters are very expensive due to the shortage of the ~3He gas and scintillation detectors are affect by gamma rays.It is great significance to explore a new detector or method for measuring the flux of neutron.Based on the principle of neutron interact with material,a new method of fast neutron flux measurement was proposed,which called neutron-induced X-ray fluorescence.In this method,the recoil proton was emitted from the Fast neutron react with hydrogen-containing material Then,the characteristic X-ray fluorescence are generated by the reaction between the recoil protons and the target material.According to the relationship between the X-ray fluorescence and the incident neutron number,the neutron flux is deduced by detecting the X-ray fluorescence number.In this paper,the Monte Carlo simulation and experimental verification were carried out to verify the feasibility of neutron-induced X-ray fluorescence method.The main research contents and conclusions are as follows:(1)A new model structure of the fast neutron flux measuring was designed by GEANT4,which was based on the principle of neutron-induced X-ray fluorescence method.Along the incident direction of the neutron,the model structure was composed of the feature target,the conversion screen and the shielding layer which used to shield the incident low-energy gamma-rays.The Geant4 toolkit was used to optimize the model structure by using the unidirectional 14 MeV neutron and 0-10 MeV exponential distribution gamma-rays as the input sources.The simulation results showed that the idea materials conversion screen,the target and the shielding were polyethylene,titanium foil and lead plate,respectively;and the best thicknesses of them were 1mm,30?m and 5mm,respectively.The angle between the neutron beam and the polyethylene plate was 5°.The X-ray detector was placed 7 cm horizontally to the neutron incident point.Both of them can effectively improve the detection efficiency.The simulation results showed that the neutron number had a good linear relationship with the X-ray fluorescence number.The neutron-induced X-ray fluorescence method was also suitable for flux measurement of other types of neutron sources.Meanwhile,the neutrons-induced X-ray fluorescence efficiency increased with the energy of incident neutrons.(2)The D-T neutron generator was used as the neutron source for the experimental setup.The feasibility of the method was verified by the experimental and simulation.The experimental structure was simulated and optimized under the point neutron source.The simulation results showed that the optimum thickness of the polyethylene and titanium foils in this case was 3mm and 50?m X-ray detector was placed in the center position to improve the detection efficiency.Experimental results showed that the low-energy gamma rays,generated by the D-T neutron generator,can be shielded by 1mm lead plate.The wavelet transform was used to deal with energy spectrum which was obtained by the silicon drift detector(SDD).The number of incident neutrons was changed by changing the detection time.There was a good linear relationship between the number of neutrons and the number of X-ray fluorescence.Then,the neutron flux was changed by changing the accelerating voltage of the neutron generator.The~3He proportional counter was also used as a reference detector.It was recorded that the trend of X-ray fluorescence counts was in good agreement with the ~3He proportional counter.It was proved that this method was feasible in fast neutron flux measurement.In this paper,neutron-induced X-ray fluorescence method was proposed to detect fast neutron flux.The feasibility of the method was studied by simulation and experiment.The results showed that this method can be applied to detect the fast neutron flux.