Superconductivity of bilayer titanium/indium thin film grown on SiO_2/Si(001)

Bilayer superconducting films with tunable transition temperature(Tc) are a critical ingredient to the fabrication of high-performance transition edge sensors. Commonly chosen materials include Mo/Au, Mo/Cu, Ti/Au, and Ti/Al systems. Here in this work, titanium/indium(Ti/In) bilayer superconducting films are successfully fabricated on SiO_2/Si(001)substrates by molecular beam epitaxy(MBE). The success in the epitaxial growth of indium on titanium is achieved by lowering the substrate temperature to-150?C during indium evaporation. We measure the critical temperature under a bias current of 10 μA, and obtain different superconducting transition temperatures ranging from 645 m K to 2.7 K by adjusting the thickness ratio of Ti/In. Our results demonstrate that the transition temperature decreases as the thickness ratio of Ti/In increases.     

被动法高浓铀年龄测量技术研究

利用HPGe-γ谱仪测量了多个年龄段的HEU样品, 获得了样品中N(214Bi)/N(234U)的值, 从而计算得到了HEU的年龄,其测量结果与参考值吻合较好。最后结合实验结果,系统分析了其它可能用于测量高浓铀年龄的方法,并对各种方法的可行性进行了分析。 结果表明, 214Bi/234U比值法是最佳的选择。N(231Pa)/N(235U)法中对γ谱如何解谱还需作进一步研究。 The HEU sample was measured by HPGe- γ spectrometry. By analyzing the detected γ spectrum, the N(214Bi)/N(234U) of the HEU sample was acquired, and the age of HEU samples was determined, which was coincided with the reference value. At last, the other potential methods of determining the age of HEU were analyzed systematically. N(214Bi)/N(234U) is more feasible,and algorithm of spectrum decomposition in N(231Pa)/N(235U) should be studied further.     

A novel acquisition method for nuclear spectra based on pulse area analysis

A novel simple method based on pulse area analysis (PAA) is presented for acquisition of nuclear spectra by a digitizer. The PAA method can be used as a substitute for the traditional method of pulse height analysis (PHA). In the PAA method a commercial digitizer was employed to sample and sum in the pulse, and the area of the pulse is proportional to the energy of the detected radiation. The results of simulation and experiment indicate the great advantages of the PAA method, especially as the count rate is high and the shaping time constant is small. When the shaping time constant is 0.5 μs, the energy resolution of PAA is about 66% better than that of PHA.     

Study on the novel neutron-to-proton convertor for improving the detection efficiency of a triple GEM based fast neutron detector

A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier(GEM) detector, which, coupled with a novel multi-layered high-density polyethylene(HDPE) as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics(IMP) at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.     

双飞秒激光脉冲诱导击穿光谱增强特性研究

在大气环境中,以钴为样品,通过单脉冲飞秒激光诱导击穿光谱及共轴双飞秒脉冲激光诱导击穿光谱的对比实验,研究了双脉冲激光诱导击穿光谱的谱线增强机制,测量了双脉冲激光诱导击穿光谱随脉冲时间间隔的变化趋势。结果表明,在最优化的脉冲时间间隔条件下,双脉冲激光诱导等离子体光谱获得明显增强。进一步,通过线性Boltzmann法得出了电子温度随脉冲时间间隔的演化,发现了谱线增强因子和电子温度随脉冲时间间隔呈现出相同的演化趋势,并经历两个明显的变化过程,得出了谱线信号强度的增强依赖于电子温度升高的结论。