A Monte Carlo study for the shielding of γ backgrounds induced by radionuclides for CDEX

The CDEX (China Dark matter EXperiment) Collaboration will carry out a direct search for WIMPs (Weakly Interacting Massive Particles) using an Ultra-Low Energy Threshold High Purity Germanium (ULE-HPGe) detector at the CJPL (China JinPing deep underground Laboratory). A complex shielding system was designed to reduce backgrounds and a detailed GEANT4 Monte Carlo simulation was performed to study the achievable reduction of γ rays induced by radionuclides and neutron backgrounds by D(γ,n)p reaction. Furthermore, the upper level of allowed radiopurity of shielding materials was estimated under the constraint of the expected goal. Compared with the radiopurity reported by other low-background rare-event experiments, it indicates that the shielding used in the CDEX can be made out of materials with obtainable radiopurity.     

A new method for high-energy pulsed Gamma measurement within intense background x-rays

The accelerator-generating 6.13~MeV pulsed Gamma by ¹⁹F(p, αγ )¹⁶⁰ reaction usually synchronizes with an intense bremsstrahlung x-ray which has a maximum energy of 1~MeV. This paper proposes a new method, named the scattering and absorbing method, to diagnose the 6.13~MeV Gamma. This method includes two parts: the detector and a scatterer placed in front of the detector. The detector converts the Gamma to electrons and then collects the electrons by a scintillator. In order to restrain the interference of the low-energy background, the scintillator collects the electrons at a small angle. The scintillator is wrapped with electro-absorbing material to absorb the low-energy electrons generated by background x-rays. The theoretical sensitivity ratio of 6.13~MeV Gamma to 1~MeV x-rays is greater than 150. The scatterer is a pretreatment tool to scatter some background x-rays away from the radial beam before they enter the detector. By varying the length, the scatterer can reduce the background x-rays to an acceptable level for the detector.     

多气隙电阻板室抗辐照性能研究

给出了为RHIC-STAR飞行时间探测器设计的多气隙电阻板室(MRPC)的辐照实验结果. 实验采用100mCi⁶⁰Co γ源, 采用不同的剂量率对MRPC进行辐照. 一个室在大剂量率2.87×10^－2Gy/h下辐照了24h后, 其性能如噪声计数率, 暗电流等均大大退化. 另一个室在相对低剂量率5.31×10^－4Gy/h下辐照了530h, 其性能没有见到任何变坏. 实验的目的是为了了解这种探测器在几年的运行中经过大剂量的辐照后的性能变化情况.     

Employing a Cerenkov detector for the thickness measurement of X-rays in a scattering background

The variation in environmental scattering background is a major source of systematic errors in X- ray inspection and measurement systems. As the energy of these photons consisting of environmental scattering background is much lower generally, the Cerenkov detectors having the detection threshold are likely insensitive to them and able to exclude their influence. A thickness measurement experiment is designed to verify the idea by employing a Cerenkov detector and an ionizing chamber for comparison. Furthermore, it is also found that the application of the Cerenkov detectors is helpful to exclude another systematic error from the variation of low energy components in the spectrum incident on the detector volume.     

利用超短脉冲激光和光电子能量微分谱直接测量窄带飞秒超紫外线XUV脉冲的时间结构

介绍用亚皮秒超短激光脉冲直接测量窄带飞秒真空超紫外线(XUV)脉冲时间结构的方法. 可以由XUV激发惰性气体产生、并在与超短脉冲激光的线性极化方向成0°或90°的方向上测量 得到的光电子能量微分谱重建这种时间结构. 谱仪的能量分辨率和所选取的能量间隔大小是 测量及计算的两个重要参数. 上述方法有很宽的时间测量范围和很高的分辨率，可以用于飞 秒计量学和与原子运动有关的超快速动力学过程的研究. 关键词： 超快速测量 超短脉冲激光 超紫外线(XUV)时间结构 光电子能量微分谱     

X射线衍射增强相衬成像相位信息提取方法研究

基于同步辐射的X射线衍射增强相衬成像有效地应用于低吸收轻物质(例如软组织)材料的内部结构检查,其关键技术是如何从DEI图像中提取出反映物体相位梯度信息的折射角图像.本文在综合研究了光学几何近似方法和多图统计方法等相位信息提取技术之后,提出了``统计--几何光学近似'相位信息提取的新方法, 并在北京BSRF形貌站上进行了实验验证. 实验表明,新方法能够大大提高光学几何近似求解的精确度和折射角图像的信噪比.     

基于数字平板探测器的高能X射线成像实验研究

为了将数字平板探测器应用到高能X射线成像无损检测,通过实验研究了平板探测器的噪声和动态范围。设计了基于平板探测器的高能X射线成像系统。通过实验研究了电子直线加速器对数字平板探测器图像采集的束流触发同步问题。     

高能X射线双能成像法中的物质识别

研究了边界能量为1—10MeV的高能X射线成像系统中采用双能成像法识别物质问题. 通过研究其物理机理, 提出了一个近似线性的数学模型; 定义了物质识别灵敏度用于评价物质识别效果; 发现了双能X射线的最优能谱分布区间. 提出并验证了面向最优能谱分布区间的双能X射线能谱调制方法, 大大提高了物质识别灵敏度, 并较好解决了不易识别薄物质的问题. 建成了9MeV/6MeV交替双能成像实验样机, 获得了物质识别着色图像. 相关实验研究结果与理论研究符合得很好.     

基于GEM探测器的时间投影室TPC的讨论

自20世纪90年代以来, GEM探测器以其高电子倍增、高空间分辨和高计数率等优势在粒子物理和辐射成像等领域得到了广泛和深入的研究, 具有广阔的应用前景. 如果将GEM作为读出探测器应用在时间投影室TPC系统上, 和传统的读出方式比较起来, 既有许多优点也有许多挑战. 目前世界上有许多机构正在研究将此方案用于将来的大型正负电子对撞机ILC. 本文论述了这些研究课题的概况, 讨论了TPC的各项关键性能指标与GEM探测器的关系及存在的问题.     

掺杂有机染料的铅锡氟磷酸闪烁玻璃及其在伽马激发下的发光

制备了掺杂有机染料芪420的铅锡氟磷酸盐杂化闪烁玻璃(lead tin fluorophosphates,简记为PTFP),测量其玻璃转变温度为75℃,染料在玻璃中的荧光发射峰位为446nm.测量了几种掺杂浓度的闪烁玻璃在⁶⁰Co源1.25MeV伽马射线激发下的发光,并和同样厚度的有机闪烁体ST401的发光进行比较,约为ST401发光的1%—2%. 关键词： 铅锡氟磷酸 闪烁玻璃 芪420 伽马