Slow positron beam was applied to study the depth profile structure of the virgin and the aged high-temperature vulcanized silicone rubber(HTV). Scanning electron microscope(SEM) images show that the surface of virgin...Slow positron beam was applied to study the depth profile structure of the virgin and the aged high-temperature vulcanized silicone rubber(HTV). Scanning electron microscope(SEM) images show that the surface of virgin sample is smooth, while the outdoor aged samples are all rough. According to the S(E) curves obtained by slow positron beam, in a depth of more than 1 μm, the S parameter of the sample aged at low-potential side keeps the same value with the virgin one;while the S values of the highpotential side aged sample remain rather low in a depth of about 5 μm. Thermo gravimetric analysis(TGA) results show that the sample in high potential side contains more inorganic constituents than that of other samples. The results are attributed to the strong electric field induced corona aging at high potential side of the composite insulator.展开更多
Simulate anneal arithmetic has been used to settle the problem of time bunching on a pulsed slow-positron beam device. This paper has searched for the parameters of the device in a large scope and achieved the time re...Simulate anneal arithmetic has been used to settle the problem of time bunching on a pulsed slow-positron beam device. This paper has searched for the parameters of the device in a large scope and achieved the time resolution within 150ps at the target with accelerating voltage in a range of 0.5-30kV.展开更多
The Beijing spectrometer Ⅲ (BESⅢ) beam pipe is in the center of the BESⅢ, which is the detector of the upgrade project of Beijing electron and positron collider (BEPC Ⅱ). Electrons and positrons collide in the...The Beijing spectrometer Ⅲ (BESⅢ) beam pipe is in the center of the BESⅢ, which is the detector of the upgrade project of Beijing electron and positron collider (BEPC Ⅱ). Electrons and positrons collide in the BESⅢ beam pipe. According to the demands of the BEPC Ⅱ, a key program of Chinese Academy of Sciences, the BESⅢ beam pipe is designed based on the finite elements analysis. The BESIII beam pipe is installed in the inner cylinder of the BESⅢ drift chamber. As a vacuum tube, the BESIII beam pipe is designed as 1 000 mm in length, 63 mm in inner diameter and 114 mm in outer diameter, respectively. The BESIII beam pipe consists of a central beryllium pipe cooled by EDM-1, the oil No.1 for electric discharge machining, and two extended copper pipes cooled by deionized water (DW). The three parts are jointed by vacuum welding. Factors taken into account in the design are as follows. ① The wall thickness of the central beryllium pipe should be designed as small as possible to reduce the multi-scattering and improve the particle momentum resolution. And the wall thickness of the extended copper pipe should be designed as large as possible to protect the detectors from the backgrounds. ②The BESⅢ beam pipe must be sufficiently cooled to avoid the damage and prevents its influence to the BESⅢ drift chamber (DC) operation. The inner surface temperature of the DC inner cylinder must be maintained at 293±2 K. ③ The magnetic permeability of the materials used in the BESⅢ beam pipe must be less than 1.05 H/m to avoid large magnetic field distortions. ④ The static pressure of the vacuum chamber of the BESⅢ beam pipe must be less than 800 μPa. The simulating results show that the designed structure of the BESⅢ beam pipe satisfies the requirements mentioned above. The structure design scheme is evaluated and adonted hv the headouarters of BEPCⅡ.展开更多
In comparison with conventional radiotherapy techniques,12C beam therapy has its significant advantage in cancer treatment because the radiation dose are mostly concentrated near the Bragg peak region and damage to no...In comparison with conventional radiotherapy techniques,12C beam therapy has its significant advantage in cancer treatment because the radiation dose are mostly concentrated near the Bragg peak region and damage to normal tissues along the beam path is thus greatly reduced.In-beam PET provides a way to monitor dose distribution inside human body since several kinds of positron-emitting nuclei are produced through the interaction between 12C beam and body matters.In this work,we study the quantitative relationship between the spatial location of the Bragg peak and the spatial distribution of positrons produced by positron-emitting nuclei.Monte Carlo package GATE is used to simulate the interactions between the incident 12C beam of different energies(337.5,270.0 and 195.0 MeV/u) and various target matters(water,muscle and spine bone).Several data post-processing operations are performed on the simulated positron-emitting nuclei distribution data to mimic the impacts of positron generation and finite spatial resolution of a typical PET imaging system.Simulation results are compared to published experimental data for verification.In all the simulation cases,we find that 10C and 11C are two dominant positron-emitting nuclei,and there exists a significant correlation between the spatial distributions of deposited energy and positrons.Therefore,we conclude that it is possible to determine the location of Bragg peak with 1 mm accuracy using current PET imaging systems by detecting the falling edge of the positron distribution map in depth direction.展开更多
For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering co...For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simulation backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.展开更多
High chromium (Cr: 16% - 19%) iron alloy with 5% and 10% manganese (Mn) fabricated in metal and sand moulds by induction melting technique were investigated for defects microstructure both in the as-cast and heat trea...High chromium (Cr: 16% - 19%) iron alloy with 5% and 10% manganese (Mn) fabricated in metal and sand moulds by induction melting technique were investigated for defects microstructure both in the as-cast and heat treated conditions. Non-destructive techniques namely Positron Lifetime Spectroscopy and slow positron Doppler Broadening studies were employed to characterize the defects in the bulk as well as surface of the alloy and their influence of metallurgical parameters. The Positron Lifetime Spectroscopy data reveals that the defect concentration is higher for sand mould alloy samples compared to metal mould ones. The reasons for fewer defects in metal mould are attributed to faster heat transfer in the metal mould. Further, heat treatment yielded spherodization of carbides in the matrix resulting in reduced defects concentration. The S-parameter profiles from Doppler Broadening studies suggest defect concentration at the surface is less in 5% Manganese and near absence of any modification of defect structure following heat treatment in 10% Manganese sample closer to surface.展开更多
In a previous paper [1] we established the possibility of the advantage of using the bombardment of electron-positron beams to produce commercial electrical energy. We consider the design of such a prototype reactor u...In a previous paper [1] we established the possibility of the advantage of using the bombardment of electron-positron beams to produce commercial electrical energy. We consider the design of such a prototype reactor using 100 KJ laser beams to produce electron-positron beams that are sent to the reactor to release the 100 KJ of energy in the form of Xrays, which creates the high temperature and pressure needed to ignite the deuterium-tritium pellets for the fusion reaction.展开更多
Two types of porous metal moderators (i.e. porous nickel layer and multi-wire tungsten layer) are proposed and tested on a slow positron beam line. A moderation efficiency of about 2×10-4 has been achieved, which...Two types of porous metal moderators (i.e. porous nickel layer and multi-wire tungsten layer) are proposed and tested on a slow positron beam line. A moderation efficiency of about 2×10-4 has been achieved, which is higher than that for W vane geometry moderator by a factor of 4.展开更多
基金Funded by the National Natural Science Foundation of China(No.21174108)the Science and Technology Project of China Southern Power Grid Co,Ltd(No.GDKJQQ20161197)
文摘Slow positron beam was applied to study the depth profile structure of the virgin and the aged high-temperature vulcanized silicone rubber(HTV). Scanning electron microscope(SEM) images show that the surface of virgin sample is smooth, while the outdoor aged samples are all rough. According to the S(E) curves obtained by slow positron beam, in a depth of more than 1 μm, the S parameter of the sample aged at low-potential side keeps the same value with the virgin one;while the S values of the highpotential side aged sample remain rather low in a depth of about 5 μm. Thermo gravimetric analysis(TGA) results show that the sample in high potential side contains more inorganic constituents than that of other samples. The results are attributed to the strong electric field induced corona aging at high potential side of the composite insulator.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10675114 and 10675115)
文摘Simulate anneal arithmetic has been used to settle the problem of time bunching on a pulsed slow-positron beam device. This paper has searched for the parameters of the device in a large scope and achieved the time resolution within 150ps at the target with accelerating voltage in a range of 0.5-30kV.
基金Key Programs of Chinese Academy of Sciences(No.KJ95T-03)
文摘The Beijing spectrometer Ⅲ (BESⅢ) beam pipe is in the center of the BESⅢ, which is the detector of the upgrade project of Beijing electron and positron collider (BEPC Ⅱ). Electrons and positrons collide in the BESⅢ beam pipe. According to the demands of the BEPC Ⅱ, a key program of Chinese Academy of Sciences, the BESⅢ beam pipe is designed based on the finite elements analysis. The BESIII beam pipe is installed in the inner cylinder of the BESⅢ drift chamber. As a vacuum tube, the BESIII beam pipe is designed as 1 000 mm in length, 63 mm in inner diameter and 114 mm in outer diameter, respectively. The BESIII beam pipe consists of a central beryllium pipe cooled by EDM-1, the oil No.1 for electric discharge machining, and two extended copper pipes cooled by deionized water (DW). The three parts are jointed by vacuum welding. Factors taken into account in the design are as follows. ① The wall thickness of the central beryllium pipe should be designed as small as possible to reduce the multi-scattering and improve the particle momentum resolution. And the wall thickness of the extended copper pipe should be designed as large as possible to protect the detectors from the backgrounds. ②The BESⅢ beam pipe must be sufficiently cooled to avoid the damage and prevents its influence to the BESⅢ drift chamber (DC) operation. The inner surface temperature of the DC inner cylinder must be maintained at 293±2 K. ③ The magnetic permeability of the materials used in the BESⅢ beam pipe must be less than 1.05 H/m to avoid large magnetic field distortions. ④ The static pressure of the vacuum chamber of the BESⅢ beam pipe must be less than 800 μPa. The simulating results show that the designed structure of the BESⅢ beam pipe satisfies the requirements mentioned above. The structure design scheme is evaluated and adonted hv the headouarters of BEPCⅡ.
基金supported in part by Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP200800031071)National Natural Science Foundation of China (No. 10975086)the National High Technology Research and Development Program ("863" Program) of China (No. 2006AA020802)
文摘In comparison with conventional radiotherapy techniques,12C beam therapy has its significant advantage in cancer treatment because the radiation dose are mostly concentrated near the Bragg peak region and damage to normal tissues along the beam path is thus greatly reduced.In-beam PET provides a way to monitor dose distribution inside human body since several kinds of positron-emitting nuclei are produced through the interaction between 12C beam and body matters.In this work,we study the quantitative relationship between the spatial location of the Bragg peak and the spatial distribution of positrons produced by positron-emitting nuclei.Monte Carlo package GATE is used to simulate the interactions between the incident 12C beam of different energies(337.5,270.0 and 195.0 MeV/u) and various target matters(water,muscle and spine bone).Several data post-processing operations are performed on the simulated positron-emitting nuclei distribution data to mimic the impacts of positron generation and finite spatial resolution of a typical PET imaging system.Simulation results are compared to published experimental data for verification.In all the simulation cases,we find that 10C and 11C are two dominant positron-emitting nuclei,and there exists a significant correlation between the spatial distributions of deposited energy and positrons.Therefore,we conclude that it is possible to determine the location of Bragg peak with 1 mm accuracy using current PET imaging systems by detecting the falling edge of the positron distribution map in depth direction.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11175171 and 11105139)
文摘For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simulation backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.
文摘High chromium (Cr: 16% - 19%) iron alloy with 5% and 10% manganese (Mn) fabricated in metal and sand moulds by induction melting technique were investigated for defects microstructure both in the as-cast and heat treated conditions. Non-destructive techniques namely Positron Lifetime Spectroscopy and slow positron Doppler Broadening studies were employed to characterize the defects in the bulk as well as surface of the alloy and their influence of metallurgical parameters. The Positron Lifetime Spectroscopy data reveals that the defect concentration is higher for sand mould alloy samples compared to metal mould ones. The reasons for fewer defects in metal mould are attributed to faster heat transfer in the metal mould. Further, heat treatment yielded spherodization of carbides in the matrix resulting in reduced defects concentration. The S-parameter profiles from Doppler Broadening studies suggest defect concentration at the surface is less in 5% Manganese and near absence of any modification of defect structure following heat treatment in 10% Manganese sample closer to surface.
文摘In a previous paper [1] we established the possibility of the advantage of using the bombardment of electron-positron beams to produce commercial electrical energy. We consider the design of such a prototype reactor using 100 KJ laser beams to produce electron-positron beams that are sent to the reactor to release the 100 KJ of energy in the form of Xrays, which creates the high temperature and pressure needed to ignite the deuterium-tritium pellets for the fusion reaction.
基金Supported by the National Natural Science Foundation of China(No.19927001 and No.10275076)
文摘Two types of porous metal moderators (i.e. porous nickel layer and multi-wire tungsten layer) are proposed and tested on a slow positron beam line. A moderation efficiency of about 2×10-4 has been achieved, which is higher than that for W vane geometry moderator by a factor of 4.