蒙地卡羅法MCNP 程式對單層屏蔽
之光子曝露增建因數研究
1 謝楊威 2*林威廷
1 慈濟技術學院放射醫學科學研究所理學碩士
2*慈濟技術學院放射醫學科學研究所助理教授
提要
本研究使用蒙地卡羅法MCNP4C、MCNP5 程式計算點均向射源（0.1、1 及10MeV），在六種不同材質（空氣、水、混凝土、鋁、鐵及鉛）的球形單層屏蔽曝露增建因數，屏蔽厚度為1 至10 個平均自由徑，並和ANSI/ANS-6.4.3-1991 報告及參考文獻相互比較。結果顯示，MCNP 程式與採用蒙地卡羅法且計算條件相似之文獻比較其結果相當一致，而ANSI/ANS-6.4.3-1991 報告的光子與物質交互作用在低原子序材質的物理反應過於簡化，其計算結果之差異性則相當明顯；MCNP 程式可考量所有光子與物質作用產生的輻射效應，故在計算點均向射源球形單層屏蔽曝露增建因數時，具備優異之準確性。
關鍵字：蒙地卡羅法、MCNP、點均向射源、曝露增建因數
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The Study of Photon Exposure Buildup Factors for
Single-Layer Shields Using MCNP Monte Carlo Code
1Yang-Wei Hsieh 2*Uei-Tyng Lin
1Master of Science, Institute of Radiological Science, Tzu-Chi College of Technology
2*Assistant Professor, Institute of Radiological Science, Tzu-Chi College of Technology
Abstract
MCNP4C and MCNP5 Monte Carlo codes are used in this study to calculate exposure buildup factors for single-layered spherical shields consisting of six kinds of different materials (air, water, concrete, aluminum, iron, and lead) at point isotropic source (0.1, 1 and 10 MeV). The thickness of shield is 1 to 10 mean free path, and the calculated results are compared with those in ANSI/ANS-6.4.3-1991 reports and reference literature. It can be seen that the results of MCNP are consistent with those of the studies which adopt Monte Carlo and similar calculation conditions. Besides, the interaction of photon and substance in ANSI/ANS-6.4.3-1991 report is excessively simplified during the physical reaction of low atomic number material, and the difference in calculated results is obvious. All of the radiation effects produced by photon and substance interaction can be considered in MCNP, so
the accuracy is high when calculating the exposure buildup factor for single-layered spherical shield at point isotropic source.
Keywords：Monte Carlo method, MCNP, point isotropic source, exposure buildup factor.