The Simulation Analysis And Experiment Tests Of Space Neutron Detector Combined With Hydrogen Material

In deep space exploration mission,the space radiation environment is the core factor for the spacecraft reliability and the health and safty of astronauts.Development of the manned space program and the exploration of deep space have raised new demand for the detetion and effect of space neutron.Secondary interaction increases the neutron fluence inside the spacecraft,even more than the proton fluence in some energy range.This paper developed a wide energy region space neutron detector for space mission,and also doing the simulation and experiment concerned.Based on Geant4,the program achieve the wide neutron energy region simulation from thermal neutron to high-energy neutron,updating the parameters of neutron response interaction model,extending the neutron energy region.Compared with the measured penetration probability of D-T neutron experiment,the error of simulation results by computer is within 0.6%to 1.6%.Finally,the reliability and applicability of the program are validated.The numerical simulation of the distribution of space atmospheric neutron is implemented by use of the built simulation platform,combined with space radiation particles transport models,expanding the model of galactic cosmic rays,the Earth's atmospheric models,field models and so on.The space atmospheric neutron flux at different heights in the atmosphere and the albedo neutron flux at the top of the atmosphere are obtained.In this paper,we introduce the transportation of the solar neutron and analysis the spectrum of the solar neutron.The primary space radiation field characteristics of the external spacecraft is obtained through the simulation.The simulation based on the parameters of the spacecraft obtained the secondary radiation field and the neutron energy spectrum distribution inside the spacecraft.According to the simulation analysis,the structural parameters such as the electrodes,structure,material,and the neutron sensitive layer thickness of proportional boron-lined counter have been obtained,also working parameters such as electric field and working pressure.The inner walls of proportional counter are coated with Isotope enriched ¹⁰B film to make cathode,in order to increase the neutron detector efficiency.Furthmore,a set of 14 annulus Epoxy sheet which are sided with ¹⁰B film are placed in the tube by the method of increasing neutron sensitive area.Compared with the previous produced detector,which is only coated ¹⁰B film in the inner walls of detector,neutron sensitive area of the new detector was increased 3.15-fold.This structural improvement greatly improved the neutron detector sensitivity.The tests showed the plateau length was increased from80V?760⁸40V?to 150V?750⁹00V?,the plateau slope was improved to 7.58%/100V from12.4%/100V.Under the same test environment,the same neutron source,and the working voltage both with 800V,the results of proportional counter experiment showed that the count rate of proportional boron-lined counter was increasd from 19cps to 50cps,while the neutron sentivity area was increased 2.63-fold.Using Geant4 software based on Monte Carlo method,this paper presented the response and detection efficiency of boron-lined proportional counter,which is covered with?55mm×250mm cylinder high-density polyethylene moderator material.The simulation results of Geant4 are in agreement with the results of ²⁴¹Am-Be neutron source experiment.It shows the reliability of simulation application.On the basis of the proportional boron-lined counter technologies,boron-lined neutron chamber was designed,neutron transport process in hydrogen materials had been studied and analyzed,for the research of multi-layer combination neutron detection technology.The high density polyethylene has high concentration of hydrogen,plays an important role in moderating neutron.Based on the simulation,the Bonner multi-cylinder neutron detector consists of a boron-lined neutron chamber including a set of 5 high density polyethylene cylinders,which is used as a fast neutron moderate and with diameters of 55,80,130,220,285mm.The high density polyethylene density is 1.0177±0.028g/cm³.High density polyethylene extended the energy range of neutrons response of boron-lined neutron chamber,from thermal neutron to tens MeV fast neutron.The experiments based on the standard neutron source were done,and had obtained the very good results.The neutron sensitivity of Bonner multi-cylinder neutron detector,while the outer diameter of high density polyethylene is 22cm,reaches a level of 8.702×10^-15A/(cm^-2·s^-1)under experimental conditions.The technological index of multi-cylinder neutron detector designed in this paper has reached the international advanced level.The experimental current data is compared with the simulation results.It is shown that the simulation results are accordant in observation data error of the experiment and the warps are less than 10%.The energy rang of 1×10^-9 MeV to 20 MeV is divided to forty-three energy bins using the logarithmic method.The response function of Bonner multi-cylinder neutron detector is obtained by Geant4 simulation.The purpose of this research is to apply the Generalized Regression Neural Network?GRNN?,to predict the neutron spectrum using the current data of Bonner multi-cylinder neutron detector.GRNN Training and testing was carried out in the MATLAB environment.All 160spectra of ORNL,IAEA,Monoenergetic,1/E neutron spectrum etc.are imported into the database,and chosen for the GRNN training.According to experimental results of Am-Be source,the current of Bonner multi-cylinder neutron detector was inputted into the unfolding spectrum software and got the preditted spectrum.The waveform and peak of preditted Am-Be neutron spectrum show a good agreement with ISO Am-Be neutron spectrum,the peak position was coincident and the average deviation of unfolding spectrum was 0.75%.