Preparation And Irradiation Characteristic Study Of Mg-Based Neutron Source Tritium Target

Deuterium/tritium(DT)fusion neutron source is one of the key devices for neutron science research and applications.Tritium target,as the core component of the neutron source,directly affects the intensity and stability of neutron production.Due to limitations such as working temperature and strong deuterium stopping power,the neutron source intensity of traditional tritium storage material,titanium hydride,is difficult to improve,which has become an important bottleneck problem restricting the further widespread application of DT fusion neutron sources.In order to increase the neutron source intensity,based on the calculation of the theoretical neutron source intensity of various hydrogen storage materials under the same conditions,Mg,which has a large hydrogen storage capacity,high tritium release temperature,and low deuterium stopping power,was selected as a new type of tritium target storage material for research.The characteristics of the Mg target were studied through experimental methods and molecular dynamics simulations.In the experimental process,deuterium isotopes were used as a substitute for tritium for research purposes.The main conclusions can be summarized as follows:1.Copper-based D-Mg targets have been prepared by physical vapor deposition.Characterization result results showed that the deuterium magnesium film had a dense structure with nano-sized particles on the surface.The deuterium release temperature was about 275℃,and its structure was mainly stable α-MgD2,with(110)and(101)phases.The D-Mg atomic ratio was approximately 1.75.The presence of oxygen in the vacuum chamber during the preparation process led to the incorporation of a certain amount of oxygen in the target.Additionally,due to the large surface area of MgD2,the oxygen content increased closer to the surface.Furthermore,there were certain amounts of MgO,Mg(OH)2,and MgCO3 on the sample surface.2.The MgD2 targets were irradiated with deuterium ions,and the neutron characteristics and irradiation damage characteristics were measured.The neutron characteristics results showed that the neutron source intensity of the MgD2 target was improved by approximately 16.8%compared to the TiD2 target.The tests also revealed that compared to the Ti target,which maintains stable neutron intensity under long-term irradiation,the neutron yield of the Mg target showed rapid decay,which accelerated with increasing deuterium ion energy and intensity.TPD-MS and XRD results indicated a significant decrease in deuterium content and decomposition of MgD2 in the irradiated MgO2 target.SEM and TEM results showed the presence of defects such as vacancies and dislocations in MgD2 under low-dose irradiation,and high-dose irradiation led to the generation of macroscopic defects,whose density and size increased with the increase in beam energy and intensity.Moreover,TEM characterization revealed the formation of a large number of bubbles inside the irradiated MgO2 target.3.Molecular dynamics simulations have been used to study the evolution of defects,bubble formation,detachment,and the influence of defects on tritium diffusion performance in irradiated MgT2.The study revealed that temperature affects the peak value of defects,but has a negligible impact on the stable number of defects.The peak value and stable number of defects are positively correlated with the PKA energy.When the amount of deuterium ion irradiation reaches a certain level,MgT2 crystal will transform into an amorphous state,leading to the formation of tritium bubbles inside the crystal.NEB results showed that the energy barrier for the formation of tritium bubbles during tritium release is higher than the energy barrier for tritium bubble release.The impact of different types of defects on tritium diffusion showed that Mg interstitials decrease tritium diffusion performance,while tritium interstitials increase diffusion performance.The presence of Mg and tritium vacancies both reduced the diffusion performance.4.Based on the evidence provided by molecular dynamics simulations regarding the effective absorption of defects by grain boundaries,Mg/Ti targets containing grain boundaries have been prepared,and their performance was tested.The results of molecular dynamics simulations showed that grain boundaries have a significant absorption effect on defects,and compared to interstitial atoms,grain boundaries have a higher absorption efficiency for vacancies.The absorption effect of grain boundaries on defects is affected by defect position and grain boundary angle.Mg/Ti composite targets containing grain boundaries were prepared experimentally,and it was confirmed through deuterium ion beam irradiation testing that the radiation resistance of the composite target was significantly enhanced.Based on these studies,Mg/Ti multilayer targets were designed and prepared,which exhibited stable neutron intensity under deuterium ion beam irradiation.In summary,this study aimed to address the problem of the difficulty in enhancing the neutron source strength in Ti targets.Based on theoretical calculations of neutron intensity,Mg,which has high theoretical neutron intensity,was chosen as the research object.MgD2 targets were prepared and there performance was tested.The results showed that the generation of internal defects in the MgD2 target under deuterium ion irradiation was the main cause of severe attenuation of neutron intensity.Molecular dynamics simulations were employed to investigate the generation of internal defects in MgT2,the formation and release of bubbles,and the effects of defects on tritium diffusion.It was proven that defects promoted the formation of bubbles inside the system,leading to tritium release.By introducing grain boundaries into MgT2 system,defects could be effectively absorbed,enhancing its radiation resistance.This conclusion was also confirmed through experimental verification.Finally,a Mg/Ti multilayer target was designed and prepared,and neutron irradiation testing with deuterium ions was conducted to validate the feasibility of enhancing radiation resistance by introducing multilayer grain boundaries within the system.