宇宙线缪子散射成像模拟与算法研究

本文验证了基于Micromegas探测器的宇宙线缪子散射成像系统进行快速核材料检测的可行性,并对实验室宇宙线缪子成像系统原型进行参数估算。基于Geant4程序开发了用于模拟宇宙线缪子物理过程、传输径迹及Micromegas探测器响应的模拟程序。在模拟数据的基础上,实现并改进了两种主要的宇宙线缪子散射成像算法。根据模拟和成像结果,1 m×1 m成像系统可在10 min内检测到被重元素屏蔽的核材料。10 cm×10 cm成像系统的缪子事例触发率为0.16 s^-1,要获得较为清晰的成像结果,要求探测器位置分辨率达到300 μm,探测器增益为1 000时实际测量事例至少需要20 h。     

基于天然μ子散射特征评估铀板内水平狭缝宽度的方法

针对经典μ子成像方法用于特殊对象结构探测的技术难点,提出了一种通过直接比较对象发生结构变化前后μ子散射特征的差异来进行形变类型和尺度判定的新思路,称为正向参比法。相比于经典的逆向反演法,该方法在原理上对于初始结构已知的特殊核对象的结构变化探测更有优势。从初步模拟结果来看,在合理的天然μ子通量下,该方法可实现铀板内亚毫米尺度水平狭缝的存在及其尺度的准确判定。     

缪子对小尺寸中低原子序数物质三维成像技术的模拟研究

缪子成像是一种利用天然本底辐射中极具穿透力的缪子射线通过散射或透射技术对高原子序数Z或隐藏物体进行无损成像的技术。当前的研究对象是大尺寸的高Z物质,而针对小尺寸的中低Z物质的成像技术在国内鲜见报道。本文提出了一种针对小尺寸中低Z物质的三维成像技术,利用Geant4软件模拟了缪致次级粒子的产生过程,模拟结果表明次级粒子主要为电子和γ光子,通过缪致次级粒子与入射缪子符合探测技术筛选入射缪子径迹,利用有限角度成像算法对待测物体进行了三维图像重建,结果表明,该技术适合于小尺寸的中低Z物质成像,尤其对小尺寸中Z物质的重建效果明显,重建图像可区分08 cm的凹槽。     

灰色关联聚类在宇宙射线μ子成像中的应用

该工作为宇宙线μ子探测裂变核材料研究中的一部分.宇宙射线μ子成像目标存在粒子数偏少的客观条件,符合灰色系统理论的“小样本”、“贫信息”的特点,首次探索应用灰色关联聚类分析提高宇宙射线μ子成像中对物质区分效率的方法.     

宇宙射线μ子探测裂变核材料的成像算法

宇宙射线μ子探测作为一种清洁源、深穿透、真正识别裂变核材料的新方法正在世界范围内日益受到重视,我国也在反恐领域开展此项研究,论文介绍了研究工作中图像重建算法(PoCA算法、期望最大化算法)以及算法模拟实验结果和分析,模拟结果初步证明了宇宙线μ子进行特殊核材料检测的可行性以及图像重建算法的有效性.     

A novel 4D resolution imaging method for low and medium atomic number objects at the centimeter scale by coincidence detection technique of cosmic-ray muon and its secondary particles

The muon radiography imaging technique for high-atomic-number objects(Z) and large-volume objects via muon transmission imaging and muon multiple scattering imaging remains a popular topic in the field of radiation detection imaging. However, few imaging studies have been reported on low and medium Z objects at the centimeter scale. This paper presents an imaging system that consists of three layers of a position-sensitive detector and four plastic scintillation detectors. It acquires data by co...     

不同测量条件下μ子源项特征模拟

采用CRY宇宙射线模拟软件包,获取不同测量条件下μ子的特征信息,研究不同条件下宇宙射线中μ子的通量、能谱、角分布等特征规律。研究结果表明:太阳活动极大时会使μ子通量降低;地磁场的影响使得赤道附近的μ子通量比极地地区要小且能谱蓝移;海拔升高则会显著增大μ子通量,但总体能量均值降低。模拟结果与相关实验结果具有很好的一致性。     

Nuclear material investigations by advanced analytical techniques

Advanced analytical techniques have been used to characterize nuclear materials at the Paul Scherrer Institute during the last decade. The analysed materials ranged from reactor pressure vessel (RPV) steels, Zircaloy claddings to fuel samples. The processes studied included copper cluster build up in RPV steels, corrosion, mechanical and irradiation damage behaviour of PWR and BWR cladding materials as well as fuel defect development. The used advanced techniques included muon spin resonance spectroscopy for zirconium alloy defect characterization while fuel element materials were analysed by techniques derived from neutron and X-ray scattering and absorption spectroscopy.     

Spin polarization and production rate studies of surface muons in a novel solenoid capture system based on CSNS

A novel surface muon capture system with a large acceptance was proposed based on the China spallation neutron source(CSNS).This system was designed using a superconducting solenoid where a long graphite target was put inside it.Firstly,the spin polarization evolution was studied in a constant uniform magnetic field.As the magnetic field can interact with the spin of the surface muon,both the spin polarization and production rate of the surface muons collected by the new capture system were calculated by the G4beamline.Simulation results showed that the surface muons could still keep a high spin polarization([90%)with different magnetic fields(0–10 T),and the larger magnetic field is,the more surface muons can be captured.Finally,the proton phase space,Courant–Snyder parameters,and intensities of surface muons of different beam fractions were given with magnetic fields of 0 and 5T.The solenoid capture system can focus proton and surface muon beams and collect p?and l?particles.It can also provide an intense energetic positron source.     

A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.     

A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the keV range to carry out muon spin rotation (LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures,and near-surface regions.The low-energy muon beam is focused and transported to the sample by electrostatic lenses.In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction,a special electrostatic device has been implemented close to the sample position.It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential.In LEμSR experiments,an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies (0.5-30 keV).Additionally,a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments.The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations.Some experimental tests were also performed and show that the simulation well describes the experimental setup.     

双能气体探测器及其刻度校正方法的研究

设计研制了一种双能气体探测器,通过模拟计算研究了探测器应用于物质识别的可行性。在模拟计算的基础上制造了双能气体探测器样机,并对4种不同种类的物质进行了X射线透射实验。实验结果表明,双能气体探测器具备物质识别能力。研究了双能气体探测器的刻度校正方法,该方法可有效提高探测器不同探测单元间的一致性。     

Cosmic-ray muon radiography of UO2 fuel assembly

A technical demonstration of cosmic-ray muon radiography of a UO₂ fuel assembly was performed at Toshiba Nuclear Critical Assembly (NCA). The fuel assembly in the NCA was imaged through obstacles such as steel and concrete. The result suggested that the method can be applicable to assess the damage to the reactors at the Fukushima Daiichi nuclear power plant. Here, both scattering and displacement methods are presented, and the results are shown to agree with Monte Carlo simulations. In addition, detailed Monte Carlo simulations of the Fukushima Daiichi reactor were performed, which showed capability of muon radiography to locate the fuel in the damaged reactors.     

基于高能X射线散射的高原子序数物质探测方法

针对核材料的探测问题,利用其高原子序数（Z）的特性,提出了基于散射能谱解析识别物质原子序数的方法。该方法通过对X射线与物质相互作用所产生的散射光子的测量和分析来进行物质识别,这些光子包括正电子湮没光子、轫致辐射光子和康普顿散射光子,携带了物质原子序数的信息。蒙特卡罗模拟计算结果表明,该方法能够分析核素的原子序数,尤其对核材料等高Z物质的分析更为有效。采用LaBr₃(Ce)探测器测量了基于7MeV电子直线加速器的多个样品的散射能谱,结果表明,该方法能有效区分高原子序数物质。     

一个基于数字示波器的实验室数据采集系统

基于数字示波器的功能,通过编程实现观测信号的自动测量和数据的在线采集和处理。不需专用或标准电子学插件,方便快捷地实现实验室小型数据采集系统的功能,并将其应用于闪烁探测器的单u标定。     

The Trigger System for the Collider Detector Facility

The trigger logic for the Collider Detector Facility (CDF) at Fermilab is described. An analog/digital system constructs triggers based on clusters of energy in the calorimetry. These triggers are then combined with signals from the muon and central tracking systems to make a global trigger. Two levels of trigger logic have been implemented: a 'Level 1' trigger which is dead-timeless, and a more sophisticated Level 2 trigger. The rejection factor provided by these two systems will be 103 - 104.     

Data acquisition for FNAL E665

The data acquisition system for FNAL (Fermi National Accelerator Laboratory) E665, an experiment to study deep inelastic muon scattering from nucleons and nuclei, is described. The system is built with the FNAL VAXONLINE and RSX DA building blocks. The discussion covers the E665 apparatus, goals for data acquisition, FNAL tools, hardware and software architecture, control and communications, data structures, monitoring and performance limitations     

See inside: The development of a cosmic ray muon imaging system to aid the clean up of the UK’s nuclear waste legacy

In recent years the use of non-intrusive and non-invasive imaging techniques to safely interrogate non-nuclear (industrial) storage vessels or process units has seen a significant increase. The nature of material found within active ‘legacy waste’ storage vessels and other radiation shielded vessels coupled with the distinct lack of access makes representative sampling or visual inspection of the vessel extremely problematic and in some cases impossible. However, until recently, the radiation shielding which is commonplace on all nuclear sites has rendered existing remote non-intrusive imaging techniques useless. This is due to the limiting penetrative power of X-rays and gamma-rays as well as lack of access for other semi-invasive techniques such as electrical and acoustic imaging. Cosmic ray muon based imaging systems have great potential. This is because muons have very high energies (up to 10¹² GeV) and therefore, offer a superior penetrative power which provides a means to ‘peer through’ objects which otherwise would be inaccessible. Such objects may include lead lined silo or vessels as well as various intermediate material transport modules. Because muons only show detectable interactions with high atomic number material they also offer a means to detect the quantity and location of heavy metal elements and their associated compounds. In this work the first attempts at two-dimensional muon attenuation mapping are described. More specifically multiple plane prototype muon detection system has been used to image the resultant attenuation maps for a number of lead phantoms. This opens up possibilities for the collation of muon trajectory data which in turn can be used to track muon events both entering and leaving the object of interest allowing attenuation based image processing. It is believed that future work in this area will serve to significantly improve both the coverage area and the spatial resolution of the system though improved detector technology providing a powerful tool for the rendering of either large or dense objects.     

A modified multi-group model of angular and momentum distribution of cosmic ray muons for thickness measurement and material discrimination of slabs

Muon tomography is a capable imaging technique to measure the geometry of high-Z objects. However,most existed algorithms used in muon tomography have obscured the effects of angular distribution and momentum spectra of cosmic ray muons and reduced the spatial resolution. We present a modified multi-group model that takes into account these effects and calibrates the model by the material of lead. Performance tests establish that the model is capable of measuring the thickness of a Pb slab and identifying the material of an unknown slab on a reasonable exposure timescale, in both cases of complete and incomplete angular data. Results show that the modified multi-group model is helpful for improvements in image resolution in real applications.     

The present status of R&D for the muon target at J-PARC: The development of silver-brazing method for graphite

At the J-PARC muon science facility, the muon target was made of an isotropic graphite (IG-43). The energy deposited by the proton beam is estimated to be 3.3 kW on graphite and 600 W on the copper frame. To alleviate the thermal stress, a titanium stress absorber is inserted between the graphite and the copper. Although graphite is known to be difficult to be brazed, the titanium is attached to the graphite through silver-brazing. In this report, we will describe the development of a silver-brazing method for graphite in the fabrication of the J-PARC muon target. A capillary test between the graphite and the titanium was performed to determine the optimal brazing conditions. The test involved bonding graphite and titanium plates while varying the gap between them in order to determine the brazing material and the optimal surface treatment of graphite. Subsequently, a trial muon-production target was fabricated using this optimized brazing method. Specimens were cut from the trial target, and bending test experiments were performed to determine the tensile and shear strength of the interface. As a result, it was confirmed that graphite could be bonded adequately through the silver-brazing.