Abstract

We present a systematic computational dose rate evaluation for a packaged 1.8-Ci ²⁴¹AmBe source using both Monte Carlo and deterministic approaches, with some experimental measurements for correlation. The ²⁴¹AmBe source is stored in an extended 55-gal-drum container. Computational dose rate analysis is performed using MCNP6 (Monte Carlo) and PENTRAN (S_N) on the Center for High Performance Computing system at the University of Utah. Limited information is available regarding internal drum shielding construction, and a reverse engineering approach is presented here to estimate the dose rate and compare with measured experimental values. Our analysis shows that a deterministic three-dimensional quadrature (S_N) and anisotropic scattering (P_N) order of S₂₀P₂ is sufficient for dose rate calculations of the ²⁴¹AmBe source with polyethylene surrounding the source as shielding material. Higher quadrature orders, i.e., at least S₇₀ for neutrons and S₄₀ for photons, are needed in the presence of air due to severe streaming effects, and this is dependent upon the distance between the source and measurement locations. With air surrounding the ²⁴¹AmBe source, the Monte Carlo method is considered to be better for neutron dose calculations while the S_N method is considered better for photon dose calculations. Good agreement from both computational verification and experimental validation are observed for the dose “hot spot” in the extended 55-gal drum. The differences noted between the MCNP6/PENTRAN calculations are within 6% for the neutron dose rate and 30% for the photon dose rate. It is observed that more than 95% of the dose is attributed to neutrons. Detailed studies including a literature data validation, PENTRAN S_N convergence study, buildup factor analysis, and dose rates with different shielding materials are presented in the narrative.

摘要

我们使用蒙特卡罗和确定性方法对打包的 1.8-Ci ²⁴¹ AmBe 源进行了系统的计算剂量率评估，并进行了一些相关性实验测量。在²⁴¹ AMBE源被存储在扩展55加仑鼓容器。使用MCNP6（蒙特卡洛）和PENTRAN（S进行计算剂量率分析_ň犹他州大学的中心高性能计算系统）。关于内部鼓屏蔽结构的可用信息有限，这里提出了一种逆向工程方法来估计剂量率并与测量的实验值进行比较。我们的分析表明，确定性的三维正交 (S _N) 和S ₂₀ P _{2 的}各向异性散射 (P _N ) 级足以计算²⁴¹ AmBe 源的剂量率，该源周围有聚乙烯作为屏蔽材料。由于严重的流动效应，在存在空气的情况下需要更高的正交阶数，即中子至少为 S ₇₀，光子至少为 S ₄₀，这取决于源和测量位置之间的距离。由于²⁴¹ AmBe 源周围有空气，蒙特卡罗方法被认为更适合中子剂量计算，而 S _N方法被认为更适合光子剂量计算。对于扩展的 55 加仑桶中的剂量“热点”，观察到计算验证和实验验证的良好一致性。MCNP6/PENTRAN 计算之间的差异在中子剂量率的 6% 和光子剂量率的 30% 以内。据观察，超过 95% 的剂量归因于中子。详细的研究，包括文献数据验证，PENTRAN小号_Ñ收敛研究中，堆积因子分析，并用不同的屏蔽材料的剂量率在叙述被呈现。