Neutron-TPC(n TPC)is a fast neutron spectrometer based on GEM-TPC(Gas Electron Multiplier-Time Projection Chamber)and expected to be used in nuclear physics,nuclear reactor operation monitoring,and thermonuclear fusio...Neutron-TPC(n TPC)is a fast neutron spectrometer based on GEM-TPC(Gas Electron Multiplier-Time Projection Chamber)and expected to be used in nuclear physics,nuclear reactor operation monitoring,and thermonuclear fusion plasma diagnostics.By measuring the recoiled proton energy and slopes of the proton tracks,the incident neutron energy can be deduced.It has higher n/γseparation ability and higher detection efficiency than conventional neutron spectrometers.In this paper,neutron energy resolution of n TPC is studied using the analytical method.It is found that the neutron energy resolution is determined by 1)the proton energy resolution(σEp/Ep),and 2)standard deviation of slopes of the proton tracks caused by multiple Coulomb scattering(σk(scattering))and by the track fitting accuracy(σk(fit)).Suggestions are made for optimizing energy resolution of n TPC.Proper choices of the cut parameters of reconstructed proton scattering angles(θcut),the number of fitting track points(N),and the working gas help to improve the neutron energy resolution.展开更多
A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities ...A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities whether on flat ground or stairs and obstacles in the city. The wheel- track coupling mechanism is designed and the stability of the bodywork of the wheelchair robot on the stairs is analyzed. In order to obtain the stability of wheelchair robot when it climbs obstacles, centroid projection method is applied to analyze the static stability, stability margin is proposed to provide the stability under some dynamic forces, and the push rod rotation angle in terms of the guaranteed stability margin is given. Finally, the dynamic model of the wheelchair robot based on Lagrange equation is established, which can be a theoretical foundation for the wheelchair control system design.展开更多
Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics,...Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics,nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM（Gas Electron Multiplier amplification）-TPC（Time Projection Chamber）, named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution,high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution（FWHM） of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10^-5 for 1.2 Me V, 1.81 Me V and 2.5 Me V neutrons respectively.展开更多
后向投影(back projection,BP)成像算法能够适应非均匀孔径,但是其运算效率过低限制了其工程应用。很多学者基于子孔径划分的原理提出了不少改进的快速后向投影(fast back projection,FBP)算法,但是目前对于子孔径划分后如何进行运动补...后向投影(back projection,BP)成像算法能够适应非均匀孔径,但是其运算效率过低限制了其工程应用。很多学者基于子孔径划分的原理提出了不少改进的快速后向投影(fast back projection,FBP)算法,但是目前对于子孔径划分后如何进行运动补偿还未有深入研究。就不同的运动情况对FBP算法的运动补偿进行了研究,包括最简单的仅有方位向误差的直线运动补偿,同时存在方位向和距离向运动误差的情况,到存在有意机动的曲线航迹,最后提出了一套完整的基于传感器测量的任意孔径快速后向投影成像算法。实测数据处理结果证明了所提的算法能够适应不同运动情况进行快速成像。展开更多
基金Supported by the National Natural Science Foundation of China(No.11275109)
文摘Neutron-TPC(n TPC)is a fast neutron spectrometer based on GEM-TPC(Gas Electron Multiplier-Time Projection Chamber)and expected to be used in nuclear physics,nuclear reactor operation monitoring,and thermonuclear fusion plasma diagnostics.By measuring the recoiled proton energy and slopes of the proton tracks,the incident neutron energy can be deduced.It has higher n/γseparation ability and higher detection efficiency than conventional neutron spectrometers.In this paper,neutron energy resolution of n TPC is studied using the analytical method.It is found that the neutron energy resolution is determined by 1)the proton energy resolution(σEp/Ep),and 2)standard deviation of slopes of the proton tracks caused by multiple Coulomb scattering(σk(scattering))and by the track fitting accuracy(σk(fit)).Suggestions are made for optimizing energy resolution of n TPC.Proper choices of the cut parameters of reconstructed proton scattering angles(θcut),the number of fitting track points(N),and the working gas help to improve the neutron energy resolution.
基金Supported by State Key Laboratory of Robotics and Systems(HIT)(SKLRS-2010-ZD-04)Capital Medical Development Scientific Research Fund(20092098)
文摘A barrier-free wheelchair robot with a mechanism coupled by wheel and track is presen- ted in this paper. Using the wheelchair, the lower limb disabled persons could be more relaxed to take part in outdoor activities whether on flat ground or stairs and obstacles in the city. The wheel- track coupling mechanism is designed and the stability of the bodywork of the wheelchair robot on the stairs is analyzed. In order to obtain the stability of wheelchair robot when it climbs obstacles, centroid projection method is applied to analyze the static stability, stability margin is proposed to provide the stability under some dynamic forces, and the push rod rotation angle in terms of the guaranteed stability margin is given. Finally, the dynamic model of the wheelchair robot based on Lagrange equation is established, which can be a theoretical foundation for the wheelchair control system design.
基金Supported by National Natural Science Foundation of China(11275109)
文摘Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics,nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM（Gas Electron Multiplier amplification）-TPC（Time Projection Chamber）, named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution,high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution（FWHM） of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10^-5 for 1.2 Me V, 1.81 Me V and 2.5 Me V neutrons respectively.
文摘后向投影(back projection,BP)成像算法能够适应非均匀孔径,但是其运算效率过低限制了其工程应用。很多学者基于子孔径划分的原理提出了不少改进的快速后向投影(fast back projection,FBP)算法,但是目前对于子孔径划分后如何进行运动补偿还未有深入研究。就不同的运动情况对FBP算法的运动补偿进行了研究,包括最简单的仅有方位向误差的直线运动补偿,同时存在方位向和距离向运动误差的情况,到存在有意机动的曲线航迹,最后提出了一套完整的基于传感器测量的任意孔径快速后向投影成像算法。实测数据处理结果证明了所提的算法能够适应不同运动情况进行快速成像。
