Study On Energy Spectrum Measurement And Characteristics Of Accelerator-based Neutron Source From Low Energy D-D/D-Be Reaction

In recent years,with the rapid development of neutron physics and neutron application technology and nuclear energy research,the study of accelerator neutron sources has become increasing attention.Especially the neutron sources of low-energy accelerators have important applications in the field of neutron physics and neutron application technology due to their low cost,miniaturisability,ease of control,and ability to produce quasi-mono-energy neutrons.In order to satisfy the need for miniaturisation and removability,Lanzhou University has developed numerous compact D-D neutron generators with neutron yield higher than 5×10⁸n/s.For better application of the compact D-D neutron generator,the energy spectrum distribution of the neutron source needs to be detailed studied.In addition,the⁹Be(d,n)¹⁰B reaction is also an exothermic nuclear reaction and can produce broad energy region ⁹Be(d,n)¹⁰B neutrons by bombarding Be with a low-energy D-beam stream from the neutron generator.Our team has proposed a new idea of developing a D-Be neutron generator.For this purpose,this thesis carries out the study of energy spectrum measurement and characteristics of the accelerator neutron source from low energy D-Be reactions.The major contents,the research results,and the conclusions of the thesis are summarised as follows:A research scheme of neutron energy spectrum measurement using the EJ309liquid scintillator detector was proposed.On the basis of the related theoretical study of fast neutron energy spectrum measurement based on the recoil proton method,the study of neutron energy spectrum unfolding algorithms was carried out,and two neutron energy spectrum unfolding programs,GRAVEL and MLEM,were developed.A simulation study of the response function of the EJ309 liquid scintillator detector has been carried out using the Geant4 Monte Carlo simulation program,and the response function of mono-energetic neutrons in the energy range 0.1 Me V-15.0 Me V with an energy interval of 0.1 Me V in the EJ309 liquid scintillator detector has been obtained.This work provides the basis for the measurement of the low-energy D-D/D-Be neutron energy spectrum based on the EJ309 liquid scintillator detector.A fast neutron energy spectrum measurement system based on the EJ309 liquid scintillator detector was established,and the experimental calibration of the energy and energy resolution of the measurement system was completed by using standard gamma sources.According to the energy resolution calibration data,the broadening study of the response function of neutrons in the EJ309 liquid scintillator detector was carried out,and the response matrix of the detector system was obtained.Using the established response matrix and the developed unfolding procedure,the viability verification of the neutron energy spectrum measurement was completed.The D-D neutron energy spectrum at the D-beam energy of 130 ke V has been experimentally measured using the compact neutron generator of Lanzhou University and the established EJ309 liquid scintillator detector system.The D-D neutron energy spectra at 30°,45°,60°,75°,90°,105°,120°,135°and,150°neutron emission directions were obtained by energy spectrum unfolding.The characteristic neutron energies of D-D neutrons at different angles were calculated using the Q equation for the D-D reaction and compared with the data of the characteristic neutron peak positions energy in the experimentally measured neutron energy spectra.The results show a good agreement,and the maximum relative deviation is no more than 5%.At the same time,on the basis of considering the absorption and scattering of neutrons by the structural material of the neutron generator and the surrounding environment,the simulation study of the D-D neutron energy spectrum at different angles was completed by using the MCNP Monte Carlo simulation program.The comparison between the simulated results and the experimental spectra shows a good agreement with each other.The preliminary experimental measurements of the D-Be neutron energy spectrum at D-beam energy of 150 ke V was carried out using the compact neutron generator and the established EJ309 liquid scintillator detector system,and the outgoing neutron energy spectrum in the 90°direction was obtained.As a result,although the characteristic neutron peak of the low-energy D-Be reaction ¹⁰B in the first excited state was observed,the D-beam energy was low due to the limitation of the maximum D-beam energy the compact neutron generator,which caused the neutron yield of the D-D reaction to being much higher than the D-Be neutron yield.The D-D neutron characteristic peak count is high,while the D-Be neutron count is too low.The unfolded neutron energy spectrum does not show all the characteristic peaks of D-Be neutrons and a neutron generator with higher D-beam energy is needed to carry out the measurement study of the low-energy D-Be neutron energy spectrum.A research scheme for the experimental measurement of the neutron energy spectrum of the low-energy ⁹Be(d,n)¹⁰B reaction using the pulsed neutron generator at the Key Laboratory of Nuclear Data of the China Atomic Energy Institute and the neutron time-of-flight method is proposed.On the basis of the completion of the neutron energy spectrum measurement method and related theory for the neutron time-of-flight spectrometer based on the BC501A liquid scintillator detector,the simulation of the neutron detection efficiency of the BC501A liquid scintillator detector was studied using the NEFF program and the Geant4 Monte Carlo program,and the detector efficiency curve was determined.The experimental measurements of the neutron energy spectra of the ⁹Be(d,n)¹⁰B reaction in the 0°and 45°directions were carried out at D-beam energies of 250 ke V and 300 ke V,and the neutron time-of-flight spectra of both angles were obtained by the neutron-gamma discrimination technique of the cross-zero time method.The low-energy D-Be neutron energy spectrum was obtained for two angles according to the conversion relationship from neutron time of flight to neutron energy.The results show that the measured neutron energy spectrum clearly shows the characteristic neutron peaks of the low energy ⁹Be(d,n)¹⁰B reaction ¹⁰B in the ground state,first excited state,second excited state and third excited state with neutron energy distribution in the range of1.0-5.0 Me V,and the characteristic peaks of the D-D reaction neutrons on the target are also observed.The characteristic neutron energies of the ⁹Be(d,n)¹⁰B and D-D reactions were calculated using the nuclear reaction Q equation and compared with the peak energies of the characteristic neutron peaks in the experimentally measured spectra.The results show a good agreement,and the maximum relative deviation is no more than 2.17%.In order to further study the characteristics of the neutron energy spectrum of the low-energy ⁹Be(d,n)¹⁰B reaction,an exclusion study of the characteristic neutron peaks of the D-D reaction on the Be target was carried out.On this basis,the intensity of the neutrons emitted from each reaction channel of the low-energy ⁹Be(d,n)¹⁰B reaction was calculated based on the neutron energy spectrum data excluding the effect of D-D neutrons on the target,and the breaching ratio data of each reaction channel were preliminarily estimated.The results show that the reaction rate of ¹⁰B in the first excited state is the highest in the low energy ⁹Be(d,n)¹⁰B reaction.