由於目前國內針對放射性設施之年劑量管制限值較一般監測儀器的偵測低限來得低，為使得設施屏蔽建物設計時能夠確實保證不會超過管制限值，唯有倚賴準確可靠的設計分析工具。然而經由天空散射途徑貢獻的這一部份劑量值的估計，一般屏蔽分析最常用的射線分析（ray analysis）與增建因數（buildup factor）方法並不適用，必須使用特殊的分析技巧。由於這些分析技巧都包含了若干程度的假設，如何引用合理的近似條件，便成為正確進行天空散射的劑量評估的一重要研究課題。
本研究主要的目的在進行加馬射線天空散射特性參數的研究，研究中將參數歸納成三個部分。第一個部分為射源特性，包括射源能量分佈、射源角度分佈及射源位置；第二個部分為介質特性，包括空氣性質、地面散射效應及屏蔽建物，第三個部分為偵測點特性，包括偵測點能量分佈、偵測點角度分佈、以及偵測點位置等。這些特性參數本身及彼此之間的交互作用對天空散射的影響十分複雜，在本文中主要針對影響劑量評估與劑量監測兩個部分進行討論。在天空散射的劑量評估部分，由於射源能量與角度分佈對劑量的影響顯著，因此當考慮體射源的問題時，須將體射源轉化為具有能量與角度分佈的等效點射源後再配合修改既有的天空散射劑量分析程式（SKYDOSE與McSKY）進行評估，方可獲得合理的結果。
此外，我們透過首次核仁積分法，建立一套適合於發展成為例行評估程式的加馬射線天空散射劑量分析方法，其中參考空氣密度之加馬射線首次碰撞核仁係以EGS4蒙地卡羅程式計算得之。這些核仁經由密度修正，則可適用於其他任意空氣密度的情況。利用首次碰撞核仁積分法計算美國國家標準實驗室的天空散射劑量評估範例問題，並與其他數種常用之評估程式進行比較，結果顯示與其他程式計算值吻合良好。相較於使用蒙地卡羅程式，此法計算所需時間甚少。另外亦利用首次碰撞核仁積分法，針對非均向射源以及數種位於不同屏蔽結構內的射源進行加馬射線天空散射劑量之評估，證實我們所提出根據首次碰撞核仁積分從事天空散射劑量評估的方法具有簡單且不失準確的特性，可適用於例行天空散射分析計算。

The annual dose limit of 5 mrem for the site boundary of the radiation facilities is much lower than the annual external radiation dose of about 60 mrem of natural background. The natural background radiation dose changes to a certain extent from site to site and with the meteorological condition, the surrounding environment, and time. It results in the dose contributed by the facility itself is much difficult to be identified by the monitoring system. Therefore, the accurate and reliable analysis tools for the radiation shielding design is required to make sure the dose beyond the limit. For the skyshine problems, however, the basic technique of ray analysis and the application of buildup factors are invalid, and more specialized techniques have to be employed. Most of these specialized techniques are based on some approximations, it becomes more important to determine the reasonable assumptions when these techniques are encountered.
The main research emphasis is to perform the characteristic study of the gamma-ray skyshine. The characteristic parameters of the gamma-ray skyshine were divided into three categories: the first is the characteristic of source, including the energy distribution, the angular distribution and position; the second is the characteristic of medium, including the air properties, the effect of ground scattering, and shielding structures; the third is the characteristic of detector, including the energy distribution of the scattered photon, the angular distribution of the scattered photon, and the position of the detector. The influences of the individual and combined parameters on gamma-ray skyshine phenomenon are very complicated. Therefore, these parameters were discussed in two respects, the effect on the evaluation and monitoring of skyshine dose rates. The effects of the energy and angular distribution of the equivalent point source have to be taken into consideration on the analysis of the skyshine dose rates when the volume source is encountered. The dedicated skyshine codes SKYDOSE and McSKY were revised to include the capability of dealing with these anisotropic sources.
Furthermore, a simplified method, based on the integral of the first collision kernel, is presented for performing gamma-ray skyshine calculations for the collimated sources. The first collision kernels were calculated in air for a reference air density by use of the EGS4 Monte Carlo code. These kernels can be applied to other air densities by making density corrections. The integral first collision kernel method has been used to calculate two of the ANSI/ANS skyshine benchmark problems and the results were compared with a number of other commonly used codes. Our results were generally in good agreement with others but only spend a small fraction of the computation time required by the Monte Carlo calculations. The scheme of the integral first collision kernel method for dealing with lots of source collimation geometry is also presented in this study.

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