高能(450kV)X射线参考辐射场附加过滤研究

Study on Additional Filtration of High Energy(450kV)X-ray Reference Radiation Field

利用MCNP程序对450kV X光机建立模型,计算各参考辐射质下的原级谱、平均光子能量。对ISO4037-1中已有范围的管电压与附加过滤片厚度关系曲线进行二次拟合,确定模拟厚度范围。利用MCNP计算各附加过滤组合下的平均光子能量值,并与外推法得出的平均光子能量值进行对比,将相对偏差最小时的附加过滤作为最终确定值。从部分能量点的模拟与测量结果的对比可看出,模拟得出的平均光子能量在2%以内与PTB及中国计量院测量结果保持一致,附加过滤最大相对偏差为18%。

The model of 450kV X-ray tube is established by MCNP code,and the primary X-ray spectrums and mean energy of each reference radiation qualities are calculated.The curve of the relationship between the existing range of tube voltage and the thickness of the additional filtration in ISO 4037-1 is fitted quadratic function to determine the thickness range required for simulation.MCNP code is used to calculate the mean photon energy of each additional filtration combination,and compared with the mean photon energy with extrapolation method.The additional filtration with the smallest relative deviation is taken as the final determined value.From the comparison of simulation and measurement results of some energy points,it can be seen that the mean photon energy obtained by simulation is within 2%,which is consistent with the measurement results of PTB and the National Institute of Metrology,and the maximum relative deviation is 18%.