Abstract Absorbed dose from gamma radiation is one of the most important safety considerations when planning a nuclear facility decommissioning. In this paper, a local method of characteristics (LMOC) is presented for gamma dose assessment in three-dimensional space. The LMOC method – an improvement on the method of characteristics (MOC) - performs local area-based ray tracking to improve the computation efficiency, and the Voronoi diagram is utilized to calculate angular weights. In order to attenuate the ray effect, the non-collision flux of the radiation source is used to construct the constant scattering source. Then the scattering term is iteratively solved to obtain the flux under each energy group. Finally, the flux-dose conversion factor is used to obtain the absorbed dose in the corresponding medium. As a variant of the MOC, LMOC inherits the advantages of MOC in processing complex geometries and natural parallelism, and can also deal with the dose assessment problem where the detecting position is far away from the radiation source. Experimental study of the proposed LMOC is performed by computing the dose rate on three different cases: Backscattering with shielding, backscattering without shielding and a general case. The result from the proposed method is then compared with that from the MCNP code and Point-Kernel method. The result shows the effectiveness of the LMOC in calculating gamma radiation, and it has better performance in the general case (

中文翻译：

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剂量评估的局部特征方法

摘要 在规划核设施退役时，伽马辐射的吸收剂量是最重要的安全考虑因素之一。在本文中，提出了一种用于三维空间中伽马剂量评估的局部特征方法（LMOC）。LMOC 方法——对特征方法（MOC）的改进——执行基于局部区域的光线跟踪以提高计算效率，并利用 Voronoi 图计算角权重。为了衰减射线效应，利用辐射源的非碰撞通量来构建恒定散射源。然后迭代求解散射项以获得每个能量组下的通量。最后，使用通量-剂量转换因子来获得相应介质中的吸收剂量。作为 MOC 的一个变体，LMOC继承了MOC在处理复杂几何形状和自然平行性方面的优势，也可以处理探测位置远离辐射源的剂量评估问题。所提出的 LMOC 的实验研究是通过计算三种不同情况下的剂量率来进行的：有屏蔽的反向散射、无屏蔽的反向散射和一般情况。然后将所提出方法的结果与 MCNP 代码和点核方法的结果进行比较。结果表明LMOC在计算伽马辐射方面的有效性，并且在一般情况下具有更好的性能（所提出的 LMOC 的实验研究是通过计算三种不同情况下的剂量率来进行的：有屏蔽的反向散射、无屏蔽的反向散射和一般情况。然后将所提出方法的结果与 MCNP 代码和点核方法的结果进行比较。结果表明LMOC在计算伽马辐射方面的有效性，并且在一般情况下具有更好的性能（所提出的 LMOC 的实验研究是通过计算三种不同情况下的剂量率来进行的：有屏蔽的反向散射、无屏蔽的反向散射和一般情况。然后将所提出方法的结果与 MCNP 代码和点核方法的结果进行比较。结果表明LMOC在计算伽马辐射方面的有效性，并且在一般情况下具有更好的性能（