Mammography x-rays standard is required to improve the quality of mammary machine and reduce the dose for w omen and staff. The molybdenum target x-rays machine is used as the radiation source and free-air cylindrical...Mammography x-rays standard is required to improve the quality of mammary machine and reduce the dose for w omen and staff. The molybdenum target x-rays machine is used as the radiation source and free-air cylindrical chamber is designed for detecting photon. Four standard radiation qualities are established w ith international standard documents as references. The Correction factors including air attenuation,scattered radiation,fluorescence,w all transmission,electron loss are studied in the four radiation quality. The uncertainty in absolute measurement of air-kerma includes air volume measurement of ionization chambers,current measurement,measurement of temperature and pressure,measurement of correction factors,physical constants and orientation of the reference distance. The relative combined standard uncertainty is 0.24%.展开更多
A free-air ionization chamber in low-energy X-ray has been designed and manufactured at the National Institute of Metrology （NIM, China） according to the defination of air-kerma. The results of a preliminary test sh...A free-air ionization chamber in low-energy X-ray has been designed and manufactured at the National Institute of Metrology （NIM, China） according to the defination of air-kerma. The results of a preliminary test show that the leakage current of ionization chamber is around 2×10^-15A, and the correction factor of ion recombination for the ionization chamber is also obtained. The free-air ionization chamber is suitable for the primary standard in low-energy X-rays.展开更多
本文概括地介绍了美国国家标准局三台自由空气电离室空气吸收改正项的测量工作。提出用抽空系统配合灵敏度较高的薄壁空腔电离室测量上述改正项的实验方法,解决了自由空气电离室本身无法实现在重过滤 X 射线束的低照射量率下精确测定空...本文概括地介绍了美国国家标准局三台自由空气电离室空气吸收改正项的测量工作。提出用抽空系统配合灵敏度较高的薄壁空腔电离室测量上述改正项的实验方法,解决了自由空气电离室本身无法实现在重过滤 X 射线束的低照射量率下精确测定空气吸收改正项的困难。同时用 Attix 方法实测了其它 X 射线束的空气吸收改正项。展开更多
Purpose Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics,spectroscopy,and X-ray diagnostics.This paper presents a dependable method of absolute measurement o...Purpose Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics,spectroscopy,and X-ray diagnostics.This paper presents a dependable method of absolute measurement of radiant power for synchrotron radiation monochromatized X-rays.Methods A free-air ionization chamber was examined closely and employed as the detector in the present work.Its measuring principle was discussed,and the correction factors were determined.Absolute measurement of radiant power for synchro-tron radiation monochromatized X-rays in the region of 6-20 keV was performed using the free-air ionization chamber at Beijing Synchrotron Radiation Facility.As a verification and an important application,photodiodes were calibrated against the free-air ionization chamber.Results Relative standard uncertainties of absolute measurement using free-air ionization chamber are about 1%.Calibration of photodiodes within the photon energy range from 6 to 20 keV has relative standard uncertainties below 1.5%.Conclusion The free-air ionization chamber is qualified to be used in many disciplines to support the measurement of opti-cal radiation.展开更多
In this paper, we simulate the exposure factor by a simple model of a flee-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to p...In this paper, we simulate the exposure factor by a simple model of a flee-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.展开更多
固有过滤层厚度是X射线参考辐射装置的重要性能参数之一,需要进行定量测量。本研究以新版本ISO 4037-1标准规范为依据,以N系列辐射质(N-20~N-350)的X射线参考辐射装置为例,通过PTW30013电离室测量不同尺寸次级光阑下的辐射野,建立符合...固有过滤层厚度是X射线参考辐射装置的重要性能参数之一,需要进行定量测量。本研究以新版本ISO 4037-1标准规范为依据,以N系列辐射质(N-20~N-350)的X射线参考辐射装置为例,通过PTW30013电离室测量不同尺寸次级光阑下的辐射野,建立符合要求的实验环境。结果表明,采用半值层法测量得到该参考辐射装置的固有过滤层厚度为0.122 mm Al;通过增加铝过滤片厚度得出N-40~N-350辐射质下4 mm Al等效固有过滤层厚度;利用单质铝金属和铍金属在不同能量下质能衰减系数的转化关系,得出N-20~N-30辐射质下1 mm铍的等效固有过滤层厚度。本研究结果可为X射线参考辐射装置固有过滤的测量提供一定的参考。展开更多
文摘Mammography x-rays standard is required to improve the quality of mammary machine and reduce the dose for w omen and staff. The molybdenum target x-rays machine is used as the radiation source and free-air cylindrical chamber is designed for detecting photon. Four standard radiation qualities are established w ith international standard documents as references. The Correction factors including air attenuation,scattered radiation,fluorescence,w all transmission,electron loss are studied in the four radiation quality. The uncertainty in absolute measurement of air-kerma includes air volume measurement of ionization chambers,current measurement,measurement of temperature and pressure,measurement of correction factors,physical constants and orientation of the reference distance. The relative combined standard uncertainty is 0.24%.
文摘A free-air ionization chamber in low-energy X-ray has been designed and manufactured at the National Institute of Metrology （NIM, China） according to the defination of air-kerma. The results of a preliminary test show that the leakage current of ionization chamber is around 2×10^-15A, and the correction factor of ion recombination for the ionization chamber is also obtained. The free-air ionization chamber is suitable for the primary standard in low-energy X-rays.
文摘本文概括地介绍了美国国家标准局三台自由空气电离室空气吸收改正项的测量工作。提出用抽空系统配合灵敏度较高的薄壁空腔电离室测量上述改正项的实验方法,解决了自由空气电离室本身无法实现在重过滤 X 射线束的低照射量率下精确测定空气吸收改正项的困难。同时用 Attix 方法实测了其它 X 射线束的空气吸收改正项。
基金the National Key R&D Program of China under Grant No.2017YFF0205102the National Natural Science Foundation of China under Grant No.11375227the Joint Funds of the National Natural Science Foundation of China under Grant No.U1632264
文摘Purpose Absolute measurement of radiant power in the X-ray region is essential for many applications in astrophysics,spectroscopy,and X-ray diagnostics.This paper presents a dependable method of absolute measurement of radiant power for synchrotron radiation monochromatized X-rays.Methods A free-air ionization chamber was examined closely and employed as the detector in the present work.Its measuring principle was discussed,and the correction factors were determined.Absolute measurement of radiant power for synchro-tron radiation monochromatized X-rays in the region of 6-20 keV was performed using the free-air ionization chamber at Beijing Synchrotron Radiation Facility.As a verification and an important application,photodiodes were calibrated against the free-air ionization chamber.Results Relative standard uncertainties of absolute measurement using free-air ionization chamber are about 1%.Calibration of photodiodes within the photon energy range from 6 to 20 keV has relative standard uncertainties below 1.5%.Conclusion The free-air ionization chamber is qualified to be used in many disciplines to support the measurement of opti-cal radiation.
基金Project supported by the National Natural Science Foundation of China (Grant No 10647109)the Foundation for Key Programof Ministry of Education,China (Grant No 208067)
文摘In this paper, we simulate the exposure factor by a simple model of a flee-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.
文摘固有过滤层厚度是X射线参考辐射装置的重要性能参数之一,需要进行定量测量。本研究以新版本ISO 4037-1标准规范为依据,以N系列辐射质(N-20~N-350)的X射线参考辐射装置为例,通过PTW30013电离室测量不同尺寸次级光阑下的辐射野,建立符合要求的实验环境。结果表明,采用半值层法测量得到该参考辐射装置的固有过滤层厚度为0.122 mm Al;通过增加铝过滤片厚度得出N-40~N-350辐射质下4 mm Al等效固有过滤层厚度;利用单质铝金属和铍金属在不同能量下质能衰减系数的转化关系,得出N-20~N-30辐射质下1 mm铍的等效固有过滤层厚度。本研究结果可为X射线参考辐射装置固有过滤的测量提供一定的参考。
