摘 要
本研究開發之加馬能譜分析法（Gamma-spectrometric analysis）量測沉積物中的鉛-210活度之技術，在與傳統β法之比較結果，顯示γ法得到的數據大於β法達1.5倍之多，其差異尚待查驗。由本實驗室調配之沉積物鉛-210射源和沉積物收集器之二樣品，送交中研院地科所鈾系暨人工核種實驗室進行比較實驗。其結果顯示兩實驗室數據間之標準偏差小於10％，與量測誤差相當，顯示雙方利用加馬能譜分析法量測鉛-210之可行性。本研究亦利用Mn-fiber萃取海水鐳的技術來配合加馬能譜分析法，以調查台灣周圍海域及南海北部海域之鐳-228及鐳-226分布。
台灣東部海域的表水鐳-228分布，主要受控於與來源之距離、水平混合和黑潮稀釋作用：於近岸及河口區有較高的活性，離開河口後遽降至1/2以下，且鐳-228/鐳-226活度比值快速遞減，顯示河口與沿岸為鐳-228主要來源。鐳-226沿蘭陽溪（LY）、磯碕（CC）及卑南大溪（PN）測線之變化甚小，大部分無明顯梯度。無河川輸入之磯碕測線完全被高溫高鹽的黑潮水盤據，測線上鐳-228/鐳-226比值均低於1。本測線夏季鐳-228濃度比春季高30％，可能是受到妮蔻兒颱風影響，造成台灣東部近岸沉積物受到擾動，將更多的鐳釋放到水中所致。利用簡單之水平一維模式，算出台灣東部海域東西向沿蘭陽溪及卑南大溪二測線之水平渦漩擴散係數Kh約為1.3 × 105 cm2s-1，此值與Nozaki et al.（1989）在日本海所得之4 × 105 cm2s-1相當。
台灣海峽主要以陸棚為主，平均水深小於50公尺，自底部沉積物往上擴散到水體中的鐳可能是主要的來源，但是受到洋流和潮流消長影響很大，使得在不同時間採樣之鐳分布不具明顯趨勢。海峽鐳-228濃度和鹽度呈負相關，其中濁水溪（CS）測線在春季時鐳-228與鐳-226均明顯離岸遞減，但是淡水河（TS）測線在同季之鐳-228往西北增加，大陸沿岸可能是海峽北部鐳-228之重要來源。
連續兩年對南海北部表水鐳-228之調查結果，顯示前後兩年（2000及2001年）春季分布型態有相似之處：北部陸棚區及呂宋島西北海域為高值區；中央海區為低值區。秋冬兩季東北季風盛行，將高鐳之大陸沿岸水及陸棚水向中央海域傳輸，表水鐳-228活度自北向南遞減，中央海域及台灣南方海域為低值區。中央海域遠離海陸邊界，鐳-228活度低；台灣南方海域之低值可能因黑潮水之稀釋。一條約略垂直200公尺等深線之測線，構成一北北西-南南東之斷面，其表水鐳-228活性隨離岸距離遞減，據以計算之水平渦漩擴散係數Kh為6.2 × 106 cm2/s，比黃等人（1996）在南沙海域推估的1.7 × 107 cm2/s者小。與Yamada和Nozaki（1986）在西北太平洋西部沿岸表水鐳-228的調查結果比較，本斷面的 值介於黑潮流域離岸200公里以內及以外之海域中的 值。

ABSTRACT
This thesis was to develop a simplified technique for the analysis of 210Pb in sediment samples with gamma spectrometry. Compared with the results of the conventional beta method, we found that the gamma method yields values that are 1.5 times higher. This discrepancy awaits further investigation. However, the results determined on two sediment-trap samples and a 210Pb source by the gamma technique agree within 10 % to those determined by the same method at the Institute of Earth Sciences, Academia Sinica. Also, using the manganese-impregnated fiber extraction technique, the distributions of 228Ra and 226Ra in surface waters around Taiwan and in the northern South China Sea（SCS） were measured by a high-purity germanium（HPGe） detector coupled with gamma spectrometry.
The distribution of 228Ra in the surface sea water off eastern Taiwan was controlled by its source function, horizontal mixing and dilution of the Kuroshio. It was higher in coastal or estuarine areas but much lower farther away from the coast line. The 228Ra/226Ra activity ratio（AR） varied in the same trend. Estuaries and coastal zones in eastern Taiwan were probably the main source for 228Ra in the adjacent sea. Concentrations of 226Ra on transect LY, CC and PN were almost constant. The AR values along the transect CC were lower than unity, because there was no estuarine input and it was entirely occupied by the Kuroshio water. The concentration of 228Ra along this transect was about 30 % higher in summer than in spring, probably because 228Ra was preferentially released from the coastal sediments by typhoon Nichole. Applying a steady-state one-dimensional diffusion model to the LY and PN lines extending from the estuarine coastal areas, we estimated a horizontal eddy diffusion coefficient of about 1.3 × 105 cm2/s for the sea off eastern Taiwan. This value is comparable to that of the Japan Sea determined by Nozaki et al.（1989）.
Taiwan Strait（TS） is mainly continental shelf with water depth less than 50 m on the average. Ra isotopes in the surface water were probably supplied by diffusion from the bottom sediments; their distributions were affected by currents and tides, and so no clear trend could be recognized when sampling was conducted in different times. 228Ra was seen inversely correlated with salinity, showing effect of the fresh water. Concentrations of 228Ra and 226Ra along the transect CS decreased away from the estuary during the spring. The 228Ra values along the TS transect in the same season increased toward the northwest, suggesting a possible source from the coastal zone of the mainland.
Distribution of 228Ra in the northern SCS was determined consecutively in 2000 and 2001. The 228Ra activities in the northern continental shelf and northwestern Luzon were higher than in the central region during the spring season. The NE monsoon prevails in fall and winter causing the longshore current to transport the shelf water of high 228Ra to the central region. The 228Ra activities of surface water decreased southward and so the central region away from land had low 228Ra values. The low 228Ra concentration observed at the sea off southern Taiwan was probably due to dilution by the Kuroshio. Based on the 228Ra distribution along a transect roughly perpendicular to the 200m bathymetric contour, we calculated a horizontal eddy diffusion coefficient, Kh of about 6.2 × 106 cm2/s, a value lower than that estimated by Huang et al.（1996）in the Nansha sea area. Compared to the Kh values estimated for the northwest Pacific by Yamada and Nozaki（1986）, this value falls in between those within and without 200 km away from land in the Kuroshio region.

誌謝…………………………………………………… Ⅰ
摘要…………………………………………………… Ⅱ
ABSTRACT……………………………………………… Ⅳ
目錄…………………………………………………… Ⅵ
圖目錄………………………………………………… Ⅷ
表目錄………………………………………………… Ⅸ
一、緒論 ……………………………………………….1
1.1加馬能譜分析法之重要性 ……………………1
1.2 海水污染擴散理論之應用 ……………….…2
1.3 海水之鐳來源 …………………………….…3
1.4 本研究之動機與目的 ……………………… 3
二、研究區域 ………………...………………………5 2.1 台灣周圍海域 ..…………………………………5
2.2 南海北部海域 ……………………………… 6
三、實驗方法 ....……………………………………11
3.1 加馬能譜分析系統A和B之比較..……………11
3.2 能量校正及效率校正..………………………12
3.3 系統A和B之樣品活性比對. …………………15
3.4 海水鐳同位素之量測方法..…………………16
3.4.1 Manganese impregnated fiber的製作方法..16
3.4.2萃取 …………………………………...………16
3.4.3 Mn-fiber吸附之效率及其穩定性…….………17
3.4.4再生氡法………………………………......…18
3.5沉積物鉛-210之簡易量測法 ……..…………19
3.5.1射源的製備…………………………....………20
3.5.2加馬能譜的校正…………………………………20
3.5.3偵測方法…………………………………………21
3.5.4數據處理…………………………………………21
3.5.5γ法與β法之結果比較 ……………….…………22
3.5.6與中研院地科所之比對………………..………24
四、台灣周圍海域鐳同位素之分布……….…………25
4.1研究背景 ………………………………………26
4.1.1東海與黃海地區…………………………………26
4.1.2台灣東北海域 ………………………….………27
4.1.3台灣西南海域……………………………………27
4.1.4台灣東部海域 ……………………….…………28
4.2春季台灣周圍海域鐳同位素之分布…….……28
4.2.1春季台灣東部海域鐳同位素之分布……………30
4.2.2春季台灣海峽鐳同位素之分布…………………33
4.3夏季台灣周圍海域鐳同位素之分布 …………34
4.4影響鐳同位素分布之因素探討 ………….………37
4.4.1河口沉積物為鐳同位素之主要來源……………37
4.4.2河川逕流量………………………………………38
4.4.3黑潮高鹽水稀釋效應……………………………42
4.4.4富鐳之大陸沿岸水………………………………42
4.5春夏兩季鐳同位素之比較 …………….…………42
4.6台灣海峽與台灣東岸海域鐳同位素之比較…..…43
4.7以一維擴散模式計算水平擴散係數………………50
4.8小結…………………………………………………51
五、南海北部海域鐳同位素之分布…………….……54
5.1南海之地理及水文…………………….………54
5.2 前人研究 ……………………………….………55
5.3 南海北部海域表水鐳-228的分布….……… 56
5.4 以一維擴散模式計算水平擴散係數 ……………63
5.5 與其他海域鐳-228測定結果的比較…………65
5.6 小結 …………………………………..……66
六、結論……………………………………….......67
參考文獻…………………………………….....……68

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