Interactions between vacancies and prismatic Σ3 grain boundary in α-Al_2O_3:First principles study

Interactions between vacancies and Σ3 prismatic screw-rotation grain boundary in α-Al_2O_3 are investigated by the first principles projector-augmented wave method.It turns out that the vacancy formation energy decreases with reducing the distance between vacancy and grain boundary(GB) plane and reaches the minimum on the GB plane(at the atomic layer next to the GB) for an O(Al) vacancy.The O vacancy located on the GB plane can attract other vacancies nearby to form an O–O di-vacancy while the Al vacancy cannot.Moreover,the O–O di-vacancy can further attract other O vacancies to form a zigzag O vacancy chain on the GB plane,which may have an influence on the diffusion behavior of small atoms such as H and He along the GB plane of α-Al_2O_3.     

铀材料快中子多重性测量方程推导

随着国际核裁军的深入推进,针对核材料的属性认证愈发受到关注.快中子多重性测量技术作为一种无损检测技术,采用闪烁体探测器进行测量,在军控核查体系中发挥着越来越重要的作用.目前对于钚材料的快中子多重性测量方法发展较为成熟,对于铀材料的快中子多重性分析模型和测量方程还处于发展中.为建立铀材料的有源快中子多重性测量方程,本文在中子多重性分析方程推导过程的基础上,根据铀钚材料二者物理过程的区别,不考虑(α,n)反应,考虑快中子散射串扰的影响,利用概率母函数完成铀材料快中子多重性测量方程的推导.在此基础上,为检验测量方程的有效性,利用Geant4搭建一套3×8的井型探测系统进行模拟测量.通过分析对比耦合系数与增殖系数的拟合函数关系、多重计数率、质量求解偏差,证实了测量方程的可靠性和准确性,对快中子多重性技术的发展具有重要意义.