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。     

Development of Directional ?erenkov Counters

The performances of a test ?erenkov counter for determining the sense of motion of relativistic particles are described. The counter was tested with an electron beam at CERN and with cosmic ray muons. Results of these tests are presented and compared with theoretical expectations.     

The Side Detection Efficiency of the Channel Multiplier

The ability of a channel multiplier to record radiation incident through its side walls has been studied, using mono-energetic MeV-electrons and protons and cosmic ray muons. The results indicate that about 25% of the total length of the detector is sensitive ta this radiation with a detection efficiency depending on particle type and energy.     

Geant4 simulation of production and interaction of muons

A set of models for Monte Carlo simulation of production and interaction of high energy muons is developed in the framework of the Geant4 toolkit. It describes the following physics processes: ionization of high energy muons with radiative corrections, bremsstrahlung, electron-positron pair production, muon induced nuclear reactions, gamma annihilation into muon pair, positron annihilation into muon pair, and into pion pair. These processes are essential for the LHC experiments, for the understanding of the background in underground detectors, for the simulation of effects related with high-energy muons in cosmic ray experiments and for the estimation of backgrounds in future colliders. The applicability area of the models extends to 1 PeV. The major use-cases are discussed.     

宇宙线μ子角分布探测装置构建

为测量近地面宇宙线μ子的天顶角分布,构建了一套由两个相互平行放置的长塑料闪烁体探测器组成的探测装置,研究了影响装置性能的主要因素,优化了装置的结构设计参数。利用优化后的装置,测量得到了μ子的天顶角分布符合cos2θ的规律。观察到了角分布的东西向不对称性,当天顶角为30°时,东西向的差异约为3.5(1.5)%。     

国产锗酸铋(BGO)闪烁体荧光的硅光二极管读出方法的研究

研究了硅光二极管的一般特性,用宇宙线μ子作为检验粒子,用硅光二极管测量了国产BGO闪烁体的光电子产额,对探测器的能量分辨、噪声和硅光二极管的带电粒子效应也进行了测量。     

宇宙射线μ子探测高Z材料的仿真研究

利用Geant4建立宇宙射线μ子探测高Z材料的仿真系统,采用最大似然算法,研究用于μ子探测的位置灵敏探测器漂移管的位置分辨率及系统成像时间对成像结果的影响。当漂移管的位置分辨率优于200μm、成像时间在1～2min内可对相对独立的高Z物质快速识别,本研究也为漂移管的设计加工提供了理论依据。     

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.     

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.     

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。     

The Pioneer 8 and 9 Cosmic Ray Detector System

An instrument designed to measure the directional properties of cosmic ray propagation in the energy range 1-63 MeV per nucleon during solar active years is described. This instrument has been flown on the interplanetary space vehicles Pioneers 8 and 9. The detector package is discussed with regard to its mechanical, electrical, and data conditioning properties. In-flight calibration procedures are briefly discussed.     

用宇宙线重核测试CR-39径迹探测器性能

本文介绍用宇宙线重核测定CR-39径迹探测器性能的方法。根据穿透探测器重核粒子径迹的蚀刻速率比V=Vr/V_g,测试了国产CR-39的探测灵敏度、一致性和均匀性。     

Experimental validation of material discrimination ability of muon scattering tomography at the TUMUTY facility

Muon scattering tomography is believed to be a promising technique for cargo container inspection, owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In this work, the material discrimination ability of muon scattering tomography is evaluated based on experiments at the Tsinghua University cosmic ray muon tomography facility,with four materials: flour(as drugs substitute), aluminum,steel, and lead. The features of the different materials could be discriminated with cluster analysis and classifiers based on support vector machine. The overall discrimination precisions for these four materials could reach 70, 95, and 99% with 1-, 5-, and 10-min-long measurement,respectively.     

Cosmic Ray Induced in MOS Memory Cells

A model for estimating the cosmic ray induced bit error rate in dynamic MOS RAMs is developed and used to calculate the bit error rate in NMDS dynamic RAMs used in an operating satellite system. The calculated error rate agrees sufficiently well with the observed error rate to conclude that cosmic ray ionization is a likely cause of observed satellite bit errors. The susceptibility of M1S RAMs to cosmic ray induced error is a result of the small charge (sub-picocoulamb) typically stored on a MDS gate to represent a data bit. Relatively small energy deposition (a few MeV) can discharge a storage node, resulting in a bit error. The heavy ion particles present in galactic cosmic rays can provide this energy, resulting in a significant bit error rate for large nmeory systems in satellites. The dynamic RAM operational factors and design factors affecting ionization-induced bit error rates are discussed.     

Cosmic-Ray-Induced Errors in MOS Devices

The results are reported for a comprehensive analytical and experimental study of galactic cosmic-ray-induced errors in MOS devices. An error rate model is described which utilizes exact expressions for a path-length distribution function and a Linear Energy Transfer (LET) spectrum for the cosmic ray environment to calculate the expected cosmic-ray-induced error rate in space for a given parallel-piped-shaped sensitive volume. The model validity is confirmed by comparison of predictions to bit-error data from devices in orbiting satellites, and to cosmic ray simulation measurements on the same device types at a cyclotron. The experimental results and model predictions are described for a wide variety of device types, including NMOS, PMOS, CMOS/bulk, CMOS/SOS, and ANOS.     

闪烁剂量仪对宇宙射线的相对灵敏度及其对测量天然贯穿辐射水平影响的估计

本文分析了用电流法或脉冲高度积分法的闪烁剂量仪对宇宙射线的相对灵敏度K_γ/k_c(K_γ、k_c分别为仪器对γ射线和宇宙射线的刻度因子)。给出了不同K_γ/K_c值下,由大水面上响应值 R_w、宇宙射线剂量率 D_c 及其屏蔽因子μ的偏差对测量室外(或室内)天然贯穿辐射剂量 D(或 D_(?))和有效剂量当量率 H_E(或(?))的偏差影响的估计公式。对室外γ辐射剂量率D_γ=4.0×10~(-8)Gy·h~(-1),D_c=3.0×10~(-8)Gy·h~(-1),H_E=5.8×10~(-8)Sv·h(-1),μ=0.9和仪器本底R_0=0.2×10~(-8)Gy·h~(-1)情况下,在k_γ/k_c=0.8时,R_w 和 D_c 偏差为10%,其对 D 和 H_B 所致偏差分别不大于1%和2.5%;当μ的偏差为10%,其对(?)和(?)的偏差分别不大于1%和2.5%。     

Gamma Ray Astronomy

Recent observations have marked the transition of gamma ray astronomy from a discovery phase to an exploratory one. This has been the result of the development of a number of very sophisticated sensitive telescopes and the opportunity to place them on space platforms. A survey of the instruments developed for this research is given together with a brief summary of the current status of the observational results. These include the studies of galactic gamma ray emission, the diffuse, presumably extragalactic, gamma radiation and localized gamma ray sources. The study of the spatial distribution of galactic gamma radiation is beginning to provide a new means for the study of galactic structure and dynamics. The diffuse emission may provide evidence of gamma ray emission in the cosmological past, although improved observations must be obtained before the picture can be clarified. The study of localized sources has shown NP0532, the Crab radio pulsar, to be a gamma ray pulsar also and strong emission from Vela may be due to supernova produced cosmic rays interacting with the remnant gas.     

球载核径迹探测器用于研究重核辐射生物效应

介绍塑料核径变探测器用于研究气球高度相对论宇宙线重核辐射生物效应的“Ｂｉｏｓｔａｃｋ”实验方法和两次气球搭载实验的初步结果。     

Position-sensitive plastic scintillator detector with WLS-fiber readout

In this paper,the design,construction,simulation,and performance of a position-sensitive plastic scintillator detector are presented.The readout of the detector uses wavelength-shifting fibers coupled with multi-anode photomultipliers(PMTs) for the x-and y-dimensions.After calibrating the multi-anode PMTs,a two-dimensional projection image of the square scintillator telescope hit by cosmic muons is demonstrated.By performing a cosmic test with the Micromegas telescope,the position resolution of the detector was determined to reach approximately8.6 mm,which is close to the value obtained in physical simulation.     

Pulsed source of ultra low energy positive muons for near-surface μSR studies

We have produced a pulsed beam of low energy (ultra slow) polarized positive muons (LE-μ⁺) and performed several demonstration muon spin rotation/relaxation (μSR) experiments at ISIS RIKEN-RAL muon facility in UK. The energy of the muons implanted into a sample is tuneable between 0.1 keV and 18 keV. This allows us to use muons as local magnetic microprobes on a nanometre scale. The control over the implantation depth is from several nanometres to hundreds of nanometres depending on the sample density and muon energy. The LE-μ⁺ are produced by two-photon resonant laser ionization of thermal muonium atoms. Currently ∼15 LE-μ⁺/s with 50% spin polarization are transported to the μSR sample position, where they are focused to a small spot with a diameter of only 4 mm. The overall LE-μ⁺ generation efficiency of 3 × 10⁻⁵ is comparable to that obtained when moderating the muon beam to epithermal energies in simple van der Waals bound solids. In contrast to other methods of LE-μ⁺ generation, the implantation of the muons into the sample can be externally triggered with the duration of the LE-μ⁺ pulse being only 7.5 ns. This allows us to measure spin rotation frequencies of up to 40 MHz.