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博碩士論文 etd-0823104-171035 詳細資訊
Title page for etd-0823104-171035
論文名稱
Title
台灣鄰近海域及南海北部沉積物之鈾釷同位素地化研究
Geochemistry of Uranium and Thorium Isotopes in Marine Sediments off Taiwan and Northern South China Sea
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
72
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2004-06-17
繳交日期
Date of Submission
2004-08-23
關鍵字
Keywords
鈾-234、釷-230、南海北部、釷-232、鈾-238
Uranium-238, Thorium-232, Thorium-230, Uranium-234, Northern South China Sea
統計
Statistics
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中文摘要
本實驗分別從南沖繩海槽西端採集了二根重力岩心(T17及T18 )及一根箱型岩心(T19 ),在台灣西南海域採集了一根重力岩心(N3)和南海北部採集了三根箱型岩心(C、D及E)以供鈾釷核種的分析,主要目的是為了測定這些核種在台灣周圍邊緣海地區沉積物中分佈及其活性比的變化,藉以推測沉積物來源及其地化意義。
在岩心中,半衰期較長的核種,如:鈾-238、鈾-234、釷-232、釷-230,在南沖繩海槽西端及台灣西南海域活性在垂直或水平方向皆變化甚微,因此其沉積物來源及沉積環境在近百年來似無變動。南沖繩海槽西端及台灣西南海域的鈾-238平均活性分別為1.65 dpm/g及1.33dpm/g;而釷-232活性平均分別為3.57 dpm/g及3.34 dpm/g。此釷活性與台灣島上頁岩、板岩及黑色片岩之釷平均活性相近,推測沉積物來源應為陸源風化碎屑物質。南海北部之鈾-238平均活性為1.37 dpm/g,釷-232的平均活性為2.73 dpm/g,後者較南沖繩海槽西端及台灣西南海域來的低。在上述研究區域中,鈾-238及鈾-234的活性並無顯著的地區性變化,其活度介於1.3∼2 dpm/g,而鈾-234/鈾-238的活性比値約為1.1,接近海水中的比値1.14。而在南海北部具有較高的釷-230活性,可能是因水深較深,使得顆粒在沉降過程中能有效地清除海水中由鈾-234衰變而來的釷-230,造成釷-230超量的現象。
由南沖繩海槽西端及台灣西南海域的鈾釷同位素之活性及其活性比來看,這兩個區域內之沉積物主要是由碎屑沉積物所組成,推測其來源主要為台灣陸源風化物;而南海北部沉積物來源則較為複雜。
Abstract
Uranium and thorium radionuclides were measured on two gravity cores (T17G and T18G) and one box core (T19B) collected from the western South Okinawa Trough (SOT), one gravity core from off shore Southwest Taiwan (N3) and three box cores (C, D and E) from the northern South China Sea (SCS) in order to examine the variations of these radionuclides and their activity ratios in the sediments of the areas and to characterize the source function of the sediments and their geochemical implication based on these nuclides. For long half-life radionuclides such as 238U, 234U, 232Th and 230Th, the activities in the cores of the SOT and Southwest Taiwan areas show no significant vertical or areal variations, implying no significant variation in sediment supply or depositional environment within the past 100 years. The average activity of 238U is 1.65 dpm/g and 1.33 dpm/g in the SOT and Southwest Taiwan areas, respectively, and that of 232Th is 3.57 dpm/g and 3.34 dpm/g, respectively. The average activities of 238U and 232Th are, respectively, 1.37 dpm/g and 2.37 dpm/g in the SCS. The mean 232Th activity is lower in the SCS than in the SOT and Southwest Taiwan. The mean 232Th activity of the sediments in the SOT and Southwest Taiwan is quite comparable to that of the shale, slate and black schist in Taiwan, suggesting that these sediments are the terrigenous detrial materials from Taiwan. The 238U and 234U activities in the cores of these two areas show no significant vertical nor areal variations with activities ranging between 1.3 and 2 dpm/g, and their 234U /238U activity ratios being about 1.1, quite close to that of seawater (1.14).
Since 238U and 234U are quite comparable among the three areas, the
higher activity of 230Th in excess over 234U in the northern SCS may be due to greater water depth that allows more 234U produced 230Th to be scavenged from the water column.
The uranium and thorium radionuclides and their activity ratios in the SOT and Southwest Taiwan sediments suggest that these sediments are the terrigenous detrial materials from Taiwan. The source function of the SCS sediments is more complex than that of the above-mentioned sediments.
目次 Table of Contents
目錄
頁次
誌謝………………………………………………………………….I
中文摘要…………………………………………………………….II
英文摘要…………………………………………………………….IV
目錄………………………………………………………………….VI
圖目錄……………………………………………………………….IX
表目錄……………………………………………………………….X
一、緒論……………………………………………………………..1
二、研究區域與樣品處理方法…………………………………….4
2.1研究區域…………………………………………………..4
2.1.1台灣東北海域………………………………………4
2.1.2 台灣西南海域………………………………………4
2.1.3 南海…………………………………………………7
2.2 採樣航次及時間…………………………………………...8
2.3 岩心的處理………………………………………………...8
2.4 燒失量(L.O.I)………………………………………………8
2.5 鈾釷放射性核種分析………………………………………10
2.5.1共沉澱……………………………………………….10
2.5.2分離純化鈾、釷元素之離子交換步驟…………… 13
2.5.3鈾釷核種之電鍍…………………………………….14
三、結果與討論………………………………………………………18
3.1實驗數據比對與重複分析…………………………………..18
3.2 有機質及含水率的變化…………………………………….18
3.3鈾核種活性分析之結果……………………………………..28
3.3.1南沖繩海槽西端之岩心………………………………..28
3.3.2台灣西南海域岩心……………………………………..29
3.3.3南海北部海域岩心……………………………………..33
3.3.4 鈾-234/鈾-238活性比值……………………………...33
3.4釷核種活性分析之結果……………………………………..38
3.4.1釷-232…………………………………………………...38
3.4.2釷-230…………………………………………………...42
3.4.3釷-228…………………………………………………..44
3.4.4釷-230/釷-232活性比值………………………………..44
3.4.5 釷-228/釷-232活性比值………………………………..55
3.5釷-232/鈾-238活性比值……………………………………..55
3.6利用超量釷-230剖面計算沉積速率…………………………58
3.6.1沉積速率之計算模式……………………………………58
3.6.2計算之沉積速率………………………………………..60
四、結論……………………………………………………………….65
參考文獻………………………………………………………………..67
中文部分………………………………………………………………..67
英文部分………………………………………………………………..69
圖目錄
圖一、自然界存在的三個天然放射性系列……………………………………… 2
圖二、岩心採樣位置圖…………………………………………………………………. 6
圖三、鈾同位素之能譜……………………………………………………………..16
圖四、釷同位素之能譜…………………………………………………………………..17
圖五、南沖繩海槽西端測站T17、T18、T19之含水率與燒失量………………24
圖六、西南海域N3測站之含水率與燒失量……………………………………..25
圖七、南海測站C、D、E之含水率與燒失量……………………………………26
圖八、南沖繩海槽西端測站T17、T18、T19之鈾同位素及其比值……………30
圖九、西南海域N3測站之鈾同位素活性及其比值………………………………32
圖十、南海測站C、D、E之鈾同位素活性及其比值………………………………...36
圖十一、台灣鄰近海域各測站之U-234/U-238活性比值與深度關係圖…………38
圖十二、南沖繩海槽西端測站T17、T18、T19之釷同位素…………………………39
圖十三、西南海域N3測站之釷同位素……………………………………………40
圖十四、南海測站C、D、E之釷同位素…………………………………………..41
圖十五、台灣鄰近海域各測站之U-234與Th-230活性關係圖………………….45
圖十六、台灣鄰近海域各測站之超量Th-230活性垂直分佈圖………………….46
圖十七、台灣鄰近海域各測站之Th-232與Th-228活性關係圖…………………47
圖十八、南沖繩海槽西端測站T17、T18、T19之釷同位素活性比值………….52
圖十九、西南海域N3測站之釷同位素活性比值………………………………...53
圖二十、南海測站C、D、E之釷同位素活性比值………………………………54
圖二十一、台灣鄰近海域各測站之Th-232與Th-230活性關係圖……………..56
圖二十二、台灣鄰近海域各測站之U-238與Th-232活性關係圖………………57
圖二十三、南海C測站沈積速率圖……………………………………………….62
圖二十四、南海D測站沈積速率圖……………………………………………….63

表目錄
表一、各區域岩心位置及水深……………………………………............................5
表二、各測站岩心表觀描述…………………………………………………………9
表三、鈾釷放射性核種分析實驗步驟………………………………………………11
表四、鈾釷核種比較實驗對照表................................................................................19
表五、T17、T18、T19及N3岩心之含水率及有機質(L.O.I.)含量.......................20
表六、南海C、D、E站岩心之含水率及有機質(L.O.I.)含量……………………22
表七、台灣東北海域三測站(T17、T18及T19)岩心中鈾釷同位素活度…………29
表八、台灣西海域測站(N3)岩心中鈾釷同位素活性……………………………..31
表九、南海三測站(C、D及E)岩心中鈾釷同位素活性…………………………..34
表十、南沖繩海槽西端三測站(T17、T18及T19)岩心鈾、釷同位素活性比值..48
表十一、台灣西海域測站(N3)岩心中鈾、釷同位素活性比值..............................49
表十二、南海北部三測站(C、D及E)岩心中鈾、釷同位素活性比值..................50
表十三、南海海盆之沉積速率………………………………………………………64
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