飛航高度的宇宙射線會造成航空機組人員可觀的輻射曝露，ICRP 60(1991)號報告中建議將飛航劑量納入職業曝露的管理範疇。至此各國航空業者開始重視對飛航劑量的評估，文獻回顧顯示絕大部分的評估模式與程式並無考量飛機結構與乘載內容對於輻射的屏蔽或散射造成的效應，因此本研究深入探討此一問題對於高空宇宙射線輻射場特性以及飛航劑量評估的影響。
本研究設計由簡單到複雜的四種模型逐步探討宇宙射線各種粒子在不同條件下的能譜與劑量變化：(1)以45m半徑的真空球體模型進行射源的驗證，確保NTHU-FDC給出的能譜可以重現在MCNP的射源描述；(2)在45m球體中填入高空密度之大氣，探討宇宙射線在空氣中散射與衰減的情形，檢視其對宇宙射線能譜與劑量率的影響；(3) 在前述模型中加入一個極簡化的飛機結構(0.5mm空心鋁圓筒)，觀察此簡化艙殼對宇宙射線能譜與劑量率的影響；(4)建置合理的飛機幾何模型，近似完整機體外型、尺寸、材質以及艙體內裝與乘載等，探討飛機結構對飛航高度下的宇宙射線輻射場能譜以及機組人員有效劑量率評估之影響。
根據前述的模擬結果，本研究總結飛航高度下宇宙射線輻射場在飛機結構內的能譜變化，並量化此一效應對飛航劑量評估的影響。飛航人員的有效劑量率在考慮合理飛機模型後會有約-10%至-17%的劑量率變化，此一變化幅度會受到不同剛度與太陽活度的影響。剛度與太陽活度較高的條件下，有效劑量衰減11.71%；剛度與太陽活度較低的條件下，有效劑量則衰減16.23%。本研究也探討乘客與燃油是否滿載的情境，結果顯示飛機滿載時有效劑量率衰減較大(12.27%)，空機則衰減較小(4.05%)。本研究提供各種不同飛機結構與乘載內容對於高空宇宙射線的量化影響，相關結果可以作為未來實際在民航客機上量測飛航劑量時的實驗設計與儀器選擇參考。

Cosmic-ray-induced radiation field at flight altitudes causes non-negligible radiation exposure to aircrew. ICRP considers aircrew to be exposed to radiation on their jobs and recommends including as occupational radiation exposure. Airline companies in some countries are therefore required to assess the in-flight radiation exposure of their aircrew. Several models and computer programs are available for the purpose. However, after an extensive survey and review of literature on this topic, the author found that almost all of the aviation dose assessments did not take into account the influence of aircraft structure on the evaluation of the doses to aircrew members. The situation motivated us to perform this study: building a reasonably accurate aircraft model and simulating the interaction between cosmic radiation with airplane structure. This study explored the variation of cosmic-ray spectra and doses at flight altitudes under several geometries and conditions: (1) A vacuum sphere with a radius of 45 meters was used to verify the equivalence of the source definition in MCNP and that given by NTHU-FDC. (2) The previous sphere was filled with high-altitude air to observe the interaction of cosmic radiation with air nuclei. (3) A cylinder with 0.5-mm-thick aluminum shell was used to estimate the interaction of cosmic radiation with aircraft outer shell. (4) A high-fidelity aircraft model of B777-300ER including interior and exterior details was built to reasonably simulate the interaction of cosmic radiation with aircraft structure. Compared with the cosmic-ray-induced radiation field in the atmosphere, the simulated result provided a detailed description about the perturbation of the radiation field due to the existence of aircraft structure. The result is useful for further improving the current methodologies used in the dose assessment of aircrew and passengers.

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