【摘要】 核设施退役产生的大体积箱型废物核素分布极不均匀，基于传统层析γ扫描（Tomographic Gamma Scanning,TGS）技术对其进行活度测量，误差可达6个数量级，难以安全处置。本研究通过提出新型的γ扫描方法，建立重建算法模型，形成基于等效面源的改进型层析γ扫描技术（Improved Tomographic Gamma Scanning,ITGS）。该方法基于不同γ扫描位置的计数率比值，计算出废物箱内核素的基本分布，最后结合效率刻度得到精准的活度重建结果。对废物箱内60Co核素不同的放射源分布开展γ扫描实验，发现了核素分布与测量参数对重建结果的影响规律，验证了方法的准确性。模拟测试结果表明：更深入的放射源位置或者更大的介质密度，都会增加活度重建的误差。在相同的测量时间内，ITGS可将测量误差可控制在一个数量级内。该方法通过合理布置测量系统对放射性废物箱进行活度重建，可以在核素分布不均匀以及高密度介质等复杂工况下取得较高的重建精度，减少了废物处置对人类和环境带来的安全隐患。更多还原

【Abstract】 [Background] Large-volume container waste generated from nuclear facility decommissioning exhibits extremely inhomogeneous nuclide distribution. Its activity measured using the traditional tomographic gamma scanning(TGS) technique shows errors of up to six orders of magnitude; this hinders its safe disposal. [Purpose]This study aims to develop an improved tomographic gamma scanning(ITGS) technique based on the equivalent surface source method and establish a reconstruction algorithm. [Methods] Firstly, based on the count rate ratios of different γ-scan positions, the basic distribution of nuclides in the waste container was calculated, and the accurate activity reconstruction results were obtained by the combination of efficiency calibration. Then, γ-scan experiment was simulated for measuring various radioactive source distributions of Co-60 nuclides in large waste containers to verify the accuracy of this method, and the influence law for the nuclide distribution and measurement parameters on the reconstruction results was discovered. [Results] Simulation results demonstrate that a deeper radioactive source location or larger medium density can increase the activity reconstruction error. However, based on the same measurement time, the ITGS measurement error can be controlled within an order of magnitude compared with the conventional TGS. [Conclusion] The proposed method achieves higher reconstruction accuracy under complex conditions such as multiple nuclide distributions and high medium density. Furthermore, it mitigates waste disposal safety hazards to humans and the environment by facilitating rational arrangements of the measurement system and activity reconstruction of radioactive waste containers.更多还原