A computational model is developed to estimate the external exposure to an arbitrary scenario describing the spatial distribution of the source in a contaminated soil by gamma-ray emitting radionuclides released after nuclear activities. This model welds together a Monte Carlo simulation approach and a mathematical transformation based on Tait–Bryan angles formalism. For Monte Carlo simulation, a source depth dependent optimized geometry describing a semi-infinite soil-cover-air medium of propagation is mathematically derived based on the physical attenuation of the gamma ray in matter. For each primary energy of interest, the proposed mathematical transformation is applied to the output of the Monte Carlo simulation to define the overlapping region between the contaminated soil volume and the proposed optimized volume. This approach made it possible to estimate the human external exposure associated with the scenario under investigation. Several scenarios were studied. The flux energy distribution of the detected radiation and the corresponding dose quantities are calculated. A benchmarking test with a direct Monte Carlo simulation and a comparison with published results in the literature show good agreement validating therefore the presented model.

中文翻译：

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估算受伽马射线发射放射性核素污染的土壤中不同源几何形状的外部照射：蒙特卡罗模拟和数学变换相结合的计算模型

开发了一个计算模型来估计任意场景的外部暴露，该任意场景描述了核活动后释放的伽马射线发射放射性核素在污染土壤中源的空间分布。该模型将蒙特卡罗模拟方法和基于泰特-布莱恩角形式主义的数学变换结合在一起。对于蒙特卡罗模拟，基于物质中伽马射线的物理衰减，以数学方式推导了描述半无限土壤覆盖空气传播介质的源深度相关优化几何结构。对于每种感兴趣的主要能量，将所提出的数学变换应用于蒙特卡罗模拟的输出，以定义受污染土壤体积和所提出的优化体积之间的重叠区域。这种方法使得估计与所调查场景相关的人体外部暴露成为可能。研究了几种情况。计算检测到的辐射的通量能量分布和相应的剂量量。使用直接蒙特卡罗模拟进行的基准测试以及与文献中公布的结果的比较显示出良好的一致性，从而验证了所提出的模型。