基于光子计数能谱CT的含能材料等效原子序数测量方法

Effective Atomic Number Measurement of Energetic Material Using Photon Counting Spectral Computed Tomography

双能CT或能谱CT可以测量材料的等效原子序数,对含能材料的成分检测和生产工艺改进具有重要意义,但现有方法存在复杂度高、设备要求高等缺点。为提高等效原子序数的测量精度,并降低设备要求和算法复杂度,提出了一种基于新型CeTe光子计数探测器的等效原子序数测量方法。该方法利用材料的衰减特性,重新推导了两个能量区间线性衰减系数之比与等效原子序数的关系。该方法不依赖于双能CT或能谱CT的专业知识,只需利用光子计数探测器对三种已知材料进行能谱CT扫描与重建,即可得到等效原子序数的标定曲线,并对未知材料进行等效原子序数测量。在实际应用中,只需保证标定实验和测量实验在相同条件下进行,即可将重建误差、探测器响应误差、射束硬化效应和散射效应等影响因素纳入到标定曲线(相当于重新对NIST数据进行了特定扫描条件下的标定),并抑制上述因素对最终结果的影响。相较于其他方法,该方法鲁棒性和通用性较强,且大幅降低了设备要求和算法复杂度。同时,该方法允许相对较宽的能量区间,可以较充分的利用X射线源所发出的光子,使检测效率满足了工业检测和医学成像的需要,具有良好的商业应用前景。实验结果表明,在当前标定范围(等效原子序数6~13)和扫描条件下,该方法测量的等效原子序数相对误差小于2%,具有较高的可靠性。在实际含能材料生产检测中,该方法在不破坏含能材料的情况下对高衰减杂质成分进行了有效判断,指出了高衰减杂质是实际生产过程中混入的高原子序数杂质,而不是高密度的含能材料。这表明该方法能够有效解决含能材料生产中的成分检测难题,并有望促进含能材料生产工艺的改进,具有重要的工程意义。

Dual-energy computer tomography(CT)or spectral CT can obtain the equivalent atomic number of materials,which is very important for the composition detection and production process improvement of energetic materials.However,the existing methods have some disadvantages,such as high complexity,high equipment requirements.In order to improve the measurement accuracy of equivalent atomic numbers,and reduce the equipment requirements and algorithm complexity,a simple method based on the new CdTe photon counting detector is proposed to obtain the equivalent atomic number of materials.In this method,the relationship between the linear attenuation coefficient ratio in two energy bins and the equivalent atomic number is re-deduced using the attenuation characteristics of materials.This method does not rely on the professional knowledge of dual-energy CT or spectral CT.Only the photon-counting detector is used to scan and reconstruct the spectral CT of three known materials,the calibration curve of the equivalent atomic number can be obtained,and the equivalent atomic number of unknown materials can be measured.In practical application,as long as the calibration experiment and measurement experiment are carried out under the same scanning conditions,the influencing factors such as reconstruction errors,detector response errors,beam hardening effects,and scattering effects can be included in the calibration curve(equivalent to re re-calibrating the National Institute of Standards and Technology data under specific scanning conditions),and the influence of above factors on the final result can be restrained.Compared with other methods,this method is more robust and versatile and greatly reduces equipment requirements and algorithm complexity.At the same time,energy bins allowed by this method are relatively wide,which can make full use of the photons emitted by the detector.Therefore,this method makes the detection efficiency meet the needs of industrial detection and medical imaging and has a good commercial application prospect.The experimental results show that relative errors of equivalent atomic numbers measured by this method are less than 2%and have high reliability under current calibration ranges(equivalent atomic number 6~13)and scanning conditions.In the actual production detection of energetic materials,this method effectively judged the high-attenuation impurities without destroying the energetic materials.It is pointed out that the high-attenuation impurities are high-atomic number impurities mixed in the actual production process,rather than high-density concentrated energetic materials.This shows that this method can effectively solve the problem of composition detection in the actual production and testing of energetic materials and is expected to promote the improvement of the energetic material production process,which has great engineering significance.