论文部分内容阅读
空气衰减对自由空气电离室是最大的修正项,对总的修正因子不确定度影响也大。本文采用钼靶X射线、真空管测试系统和圆柱型自由空气电离室测量电离电流,用EGSnrc(Electron Gamma Shower)程序模拟恒压管对X射线束额外损失的影响;用抽真空法对圆柱型自由空气电离室空气衰减修正因子的测量,修正了实际测量中圆柱型自由空气电离室限束光阑入射面到收集极这段距离的空气衰减,得到准确的电离电流测量值。结果表明:自由空气电离室的电离电流与恒压管的压强成正比,恒压管对于X射线束额外损失小于0.5%;在钼靶X射线基准的4个辐射质条件下测得的圆柱型自由空气电离室空气衰减修正因子与德国物理技术研究院(The Physikalisch-Technische Bundesanstalt,PTB)的测量结果比较,呈现相同的变化趋势,符合实验要求和国际标准。圆柱型自由空气电离室空气衰减修正因子的实验测量对于钼靶X射线空气比释动能的绝对测量具有科学参考价值。
Air attenuation is the largest correction for the free air ionization chamber and has a large effect on the overall correction factor uncertainty. In this paper, ionization current was measured by mammography X-ray tube, vacuum tube test system and cylindrical free air ionization chamber. The effect of constant pressure tube on extra loss of X-ray beam was simulated by EGSnrc (Electron Gamma Shower) program. Air ionization chamber air attenuation correction factor measurement to correct the actual measurement of cylindrical free air ionization chamber limiting beam incident surface to the collection of this distance the air attenuation, accurate ionization current measurements. The results show that the ionization current of the free air ionization chamber is proportional to the pressure of the constant pressure tube, and the additional loss of the constant pressure tube to the X-ray beam is less than 0.5%. In the case of 4 radium conditions based on molybdenum target X-ray, Free air ionization chamber air attenuation correction factor and the German Institute of Physical Technology (The Physikalisch-Technische Bundesanstalt, PTB) measurements showed the same trend of change, in line with experimental requirements and international standards. Experimental Measurement of Air Attenuation Correction Factor for Cylindrical Free Air Ionization Chamber is of Scientific Reference Value for Absolute Measurement of Moment Energy of Molybdenum Target X - ray Air.