层析γ扫描技术研究

Research on tomographic gamma scanning technique

层析γ扫描技术是放射性材料无损分析技术中最先进的分析技术之一,能够准确定量测量密闭容器内中、高密度非均匀介质中的放射性核素及其含量,它是核设施中可回收物以及核废物测量分析的主要方法.本文较先在国内开展了层析γ扫描技术的研究,对该技术所涉及的探测效率刻度、透射测量图像准确重建和发射测量图像快速重建三个关键技术进行了计算机模拟研究和实验研究.采用蒙特卡罗方法对层析γ扫描装置的探测效率进行刻度;针对透射测量图像重建,创建了一种新的图像重建算法;针对发射测量图像快速重建,提出线衰减校正因子的计算公式,并采用"预运算"方法,显著提高了发射图像的重建速度.计算机模拟研究和实验研究结果表明:应用本文提出的图像重建算法,层析γ扫描透射和发射图像重建值与参考值的相对均偏差小于10%,能够满足层析γ扫描装置的实际需要,更好地解决了层析γ扫描技术中的三个关键技术,为我国层析γ扫描装置的研制奠定了基础.

Tomographic gamma scanning （TGS） method is one of the most advanced non-destructive assay （NDA） method and widely used to assay the location and quantity of selected radioisotopes in scraps and wastes within sealed containers. TGS method can determine quantitatively with high accuracy transuranic nuclides in heterogeneously distributed media with medium- and high-density. In the paper, we begin a prior investigation on TGS technology in China. Considering the characteristics of TGS, three key techniques, the detection efficiency calibration, the accurate reconstruction methods of TGS transmission image and fast reconstruction techniques of TGS emission image, are researched deeply both in simulation and experimental aspects. Calibration of the TGS equipment is solved with MC method. A MC statistical iteration method is proposed for reconstructing transmission image. A formula is deduced to calculate the correction factor of linear attenuation. Algebra iteration method is used for reconstructing emission image in the emission measurement. At the same time, the pre-calculation method is used during reconstructing TGS emission image for saving computation time. Computer simulation and experimental results show that the relative errors, between reconstruction values of TGS images and reference values, are less than 10%. Therefore, having solved the three key techniques in TGS establishes foundation for developing TGS apparatus in China.