高能闪光照相中的能谱优化

Energy spectrum optimization in high-energy flash X-ray radiography

在高能闪光照相技术中,提高图像接收平面上直穿与散射的比值有利于有效信息的提取。利用蒙特卡罗方法对法国实验客体的照相过程进行模拟,得到图像接收区域直穿分量与散射分量的能谱分布,依据其分布的特点提出了利用能谱优化来提高接收区域直散比的方法,指出添加衰减屏可以达到能谱优化的效果。依据线吸收系数的变化趋势以及实际加工的难度选择钽作为优化能谱的材料,并根据最小照射量的限制得到了最大的衰减屏厚度。最后通过蒙特卡罗模拟,指出添加9 mm的衰减屏能够对照相结果的优化程度最好,照射量满足要求,而直散比上升到原来的3倍左右。

In high energy flash radiography, enhancing the direct-to-scattered ratio（DSR） in receiving plane is favorable to the derivation of effective information. Monte-Carlo method is used to simulate the radiography process of French test object （FTO）. Energy spectrum distribution of direct and scattering fluxes is obtained within the receiving domain. The method to improve the DSR in the receiving domain by energy spectrum optimization is proposed according to the distribution property. It is found that energy spectrum can be optimized by inserting an attenuation screen. Owing to its low absorption coefficient, tantalum is adopted as the material to optimize the energy spectrum with concerning practical manufacture condition. The maximum thick- ness of the attenuation screen is derived according to the minimum radiation dose. The Monte-Carlo simulation shows that the 9 mm tantalum attenuation screen can best optimize the radiography results, the radiation dose is sufficient and the DSR can be raised to three times higher.