| 2H(d,n)3He(D-D) and 3H(d,n)4He(D-T) intense neutron generator plays a significant role in supplying quasi-mono-energetic neutrons, which can produce fast neutrons with high yields. It has applied in neutron physics, neutron applications, and experimental measurement for nuclear data, which has also promoted the study of a series of interdiscipline and research field. 9Be(d,xn) nuclear reaction can also produce fast neutrons with the low incident-deuteron-energy, neutron yields can catch up with the 2H(d,n)3He reaction. Neutron source of 9Be(d,xn) reaction is the typical continuous spectrum distribution, and the beryllium metal target is chemically stable, can be machined into convenient shapes, and is capable of withstanding high beam currents of m A and operating over a long lifetime due to its higher melting point(1280 ℃) and better thermal conductivity, which has received an attention and research. With the development and requirement for the new nuclear power system, the Fast Breeder Reactor(FBR), the Molten Salt Reactor(MSR), and the Accelerator Driven Sub-critical System(ADS), attach great importance to the nuclear data research for neutron-induced actinide fission. For evaluating the nuclear data, on the one hand, the experiments on fast neutron-induced actinide fission have been carried out by using an accelerator-based neutron source. On the other hand, it is necessary to develop theoretical models or computer programs, which can calculate the nuclear data for fission reaction.In this thesis, the physical design of the intense ne utron generator has been finished, and the neutron fields produced by 2H(d,n)3He, 3H(d,n)4He and 9Be(d,xn) reaction have been calculated. What’s more, experimental measurement processes have been simulated for fast neutron-induced actinide fission. Last but not the least, a novel and global potential-driving model with more well-determined parameters has been proposed, which can calculate and simulate the physical process of fast neutron-induced actinide fission. The main contents, results and conclusions are shown in following.1) The physical design of transport line for deuterium beam in the intense neutron generator.According to the overall technical indicators of the intense neutron generator, the design scheme uses firstly analyzing manner. For the overall design scheme, high current ECR ion source provides mixed deuterium ions beam, including D+, D2+ and D3+. Solenoid magnetic lens focus the mixed deuterium ions beam in order to make them enter into analysis magnet. Mixed deuterium ions can be selected and separated in analysis magnet, only remaining the single deuterium ion(D+). D+ ions will be accelerated in intense accelerating tube with high voltage of 400 k V, and then which will be focused by the three unit quadrupole magnetic lenses. Finally, D+ ions bombard on the rotary target with water-cooling, typical reactions occur including 2H(d,n)3He, 3H(d,n)4He, and 9Be(d,xn) reaction, which will produce neutrons.Based on the simulation of the extraction system of ECR ion source by PBGUNS code, the extraction structure is set to three-electrode, the beam parameters of D+ have been provided. The low-energy transmission line with firstly analyzing, intense accelerating tube, and the last transmission line have been designed and simulated by POISSION/SUPERFISH code. Moreover, BEAMPATH code simulates transport of D+ beam in the intense neutron generator, which provides the value of parameters. As shown in results, the designed intense neutron generator can transport the D+ ions to the target with the beam-spot within Ф20 mm.Rotary target with water-cooling can control the temperature to keep the operation for the intense neutron generator. According to the calculation by TTS code, the designed target can ’t bear the intense D+ beam with 450 ke V/40 m A. It can be operated under 26 m A. It is necessary to study and develop the rotary target in the near future.2) Calculation and evaluation of the neutron energy spectrum, angular distribution, and integrated yield of 2H(d,n)3He, 3H(d,n)4He or 9Be(d,xn) neutron source.Neutron energy spectrum, angular distribution, and integrated yield of 2H(d,n)3He and 3H(d,n)4He reaction with deuteron-energy lower than 1.0 Me V are calculated by the Multi-layer model. The integrated neutron yield of 2H(d,n)3He or 3H(d,n)4He neutron source changes along with increasing deuteron energy. There are also different integrated neutron yields for Ti Dx or Ti Tx targets. Moreover, neutron energy spectrum of 2H(d,n)3He or 3H(d,n)4He neutron source with widening distributions are different for different neutron emission-angle. Similarly, there are wider distributions for 0° or 180° and narrow distributions for 90°—120°. One can see that the 2H(d,n)3He and 3H(d,n)4He neutron source seem to the mono-energetic neutrons in the angle of 90°—120°. The angular distributions of 2H(d,n)3He and 3H(d,n)4He neutron source are specially anisotropic, this tendency will be more obvious with increasing the incident-deuteron-energy.The Multi-layer model is also developed to calculate the neutron energy spectrum, angular distribution, and integrated yield of the 9Be(d,xn) reaction on a thick beryllium target as an accelerator-based neutron source in the incident-deuteron-energy range from 0.5 to 20.0 Me V. Typical computational results are presented, and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of the 9Be(d,xn) reaction with a thick Be target. The calculated results can well agree with the experimental data.On the basis of D+ beam indicators(450 ke V/40 m A), the integrated neutron yield would reach to 2.2×1011 n/s, 1.1×1013 n/s and 3.0×1011 n/s for 2H(d,n)3He, 3H(d,n)4He or 9Be(d,xn) neutron source, respectively.The deviation of the calculated data relies on the thin-target approximation method, the cross section, and the stopping power data. Errors produced by the thin-target approximation method could be negligible, if the thick target is divided into thin enough layers. The maximum deviation of the stopping power from the SRIM-2010 code is about 14%. The deviation of the calculated data is lower than 15% without regard to the errors from cross sections.3) Simulation of the fission yields, kinetic energy, fission neutron spectrum and decay γ-ray spectrum for fission reactions induced by 3H(d,n)4He neutron source.Based on the calculated results of neutron energy spectrum and angular distribution for 3H(d,n)4He neutron source with the incident deuteron energy of 450 ke V, the characteristic of 3H(d,n)4He neutron source is accurately described in Geant4 code. 232Th(n,f) and 238U(n,f) reactions induced by 3H(d,n)4He neutron source are simulated by Geant4 code.Monte Carlo calculates the fission yields in the inside and outside of the target sample(232Th or 238U), which rely on the thickness of the sample, intensively. The share of the fission-fragments deposition inside the sample changes with increasing sample thickness. The share can reach ~99.90 % for the sample thickness of 0.8 mm, and slowly changes along with increasing sample thickness. In view of machining technology and planeness, the thickness of sample is determined to be 1.0 mm, then 99.92 % fission-fragments deposit in the thorium sample. This value can be applied in experimental measurement.Geant4 simulates and calculates the fission yields distributions for 232Th(n,f) or 238U(n,f) reactions. For 232Th(n,f) reaction, the appearance of the calculated yields distributions show a good agreement with the experimental and evaluated nuclear data. But for 238U(n,f) reaction, there are difference between the calculated yields distributions and the experimental o r evaluated nuclear data, particularly for the range of A=105-125. It is indicated that Geant4 fission model has its limits for calculating the fission reactions. Therefore, it is necessary to further study on physical mechanism of fission reaction, and develop a new physical model with more scientific and accurately to calculate and simulate the fission reactions.Kinetic energy distributions and fission neutron spectrum can also be simulated by Geant4 for 232Th(n,f) or 238U(n,f) reaction.What’s more, Geant4 code simulates and calculates the decay γ-ray spectrum with different cooling times for 232Th(n,f) or 238U(n,f) reaction. The structure of high-purity germanium(HPGe) coaxial detector is described accurately in the Monte Carlo simulation. It is possible to identify the kinds of fission products of 232Th(n,f) or 238U(n,f) reaction by analyzing the γ-ray spectrum. It is possible to distinguish almost more than 30 fission products for 232Th(n,f) or 238U(n,f) reaction.4) Development and evaluation of potential-driving model to study on pre-neutron-emission mass distributions for neutron-induced actinide fission.Based on the dinuclear system(DNS) model and the characteristics of mass distributions for fission fragments, a novel and global potential-driving model with more well-determined parameters is proposed by uniting asymmetric fission potential and symmetric fission potential. The potential-driving model can simulate and calculate the driving potential for neutron-induced actinide nuclei fission, which reflect the fission state at the breakage moment. Taking explicit account of shell-correction terms and energy-dependence evaporation neutrons for(n,xnf) reaction, the potential-driving model can precisely calculate pre-neutron-emission mass distributions for neutron-induced actinide nuclei(232Th, 235 U, 238 U, 237 Np, 239Pu) fission for the incident-neutron-energy up to 160 Me V. The potential-driving model can reproduce the experimental data reasonably well by observing the appearance of the calculated results in this work show a good agreement with the experimental data, which can also predict the mass distributions of fission fragments for unmeasured energies regions with a good accuracy.Based on the potential-driving model, Geant4 code simulates physical process of D-T neutron-induced actinide nuclei(232Th, 233 U, 235 U, 238U) fission, calculates fission yields for independent yield and cumulative yield. Compared with experimental data, ENDF/B-VII.1 evaluated data and the data calculated by the Geant4 fission model, the results calculated by the potential-driving model are in good agreement with experimental data and ENDF/B-VII.1 evaluated data, are better than those data calculated by the Geant4 fis sion model. Compared to the Geant4 fission model, not only can the potential-driving model describe the fission potential at the breakage moment, calculate pre-neutron-emission mass distributions with high precision, but also can be applied in Monte Carlo program for calculating the decay process in fission reaction. With higher computational accuracy and more predictive ability, the potential-driving model represents a significant advance with regard to application. |
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