High-density and narrow size-distribution InAs quantum dots formed by a modified two-step growth

We develop a modified two-step method of growing high-density and narrow size-distribution InAs/GaAs quantum dots (QDs) by molecular beam epitaxy. In the first step, high-density small InAs QDs are formed by optimizing the continuous deposition amount. In the second step, deposition is carried out with a long growth interruption for every 0.1 InAs monolayer. Atomic force microscope images show that the high-density ($\sim $5.9$\times $10$^{10}$\,cm$^{ - 2})$ good size-uniformity InAs QDs are achieved. The strong intensity and narrow linewidth (27.7\,meV) of the photoluminescence spectrum show that the QDs grown in this two-step method have a good optical quality.     

核医疗船反应堆屏蔽初步设计及优化

核医疗船的概念是在现有微堆(MNSR)技术的基础上提出的,它基于IAEA的癌症关怀项目,开发配备硼中子俘获治疗技术(BNCT)的远洋核医疗船,该项目开辟核科技应用的新领域。核医疗船的反应堆设计参考了已建成的医院中子照射器-1型(IHNI-1)反应堆,该堆采用重混凝土作为主要屏蔽材料,水池为方形,其体积和质量都很大,不能满足船用要求。为了使反应堆能够满足船用要求,使用蒙特卡罗方法对医院中子照射器的反应堆屏蔽系统进行重新设计和优化,通过对多个方案的综合对比,最终确定采用不锈钢、含硼聚乙烯为屏蔽材料,并将水池设计成结构紧凑的圆柱形结构,该屏蔽方案在保证安全的基础上,使屏蔽系统的质量和体积大大降低,满足了船用要求。