臺灣博碩士論文加值系統

在鈾的放射性序列（U-decay series）中的鈾同位素值與含量已被廣泛地應用在地球科學的相關研究中，其分析測量技術已有許多發展，例如使用α粒子計數儀（α Spectrometer）、熱游離質譜儀儀（Thermal Ionization Mass Spectrometer： TIMS）與高解析度感應耦合電漿質譜儀（High Resolution Inductively Coupled Plasma Mass Spectrometer： HR-ICPMS），而本論文工作乃著力於利用造價較TIMS與HR-ICPMS為“平民化”的四極桿式感應式耦合電漿質譜儀（Quadrupole Inductively Coupled Plasma Mass Spectrometer：Q-ICPMS）的分析技術及數據處理，以期求得能如同TIMS與HR-ICPMS相近之高精密度與高靈敏度的鈾同位素值與鈾濃度之測量。而此方法的突破將可達到快速、大量標本處理且高精密度及靈敏度的鈾同位素與濃度分析的優點，使鈾同位素及含量在地球科學研究主題及自然環境標本之應用上更臻寬廣。
本論文工作為達上述的目標，所採用之策略為（一）以微濃縮霧化進樣系統（micro-concentric nebulization introduction system）取代質譜儀之霧化器（nebulizer），以提高儀器靈敏度（sensitivity）並降低標本量；（二）運用測量值之標準偏差法過濾雜訊（standard deviation filter）提高測量精確度；（三）使用233U-236U雙示蹤劑標準添加法（double spike standard addition）作質量分化校正，並採用標準樣品穿插校正法（standard bracketing method）消除比值飄移現象（ratio drifting），以確立測量精確度。
利用一標準樣品NBL 112A（New Brunswick Laboratory 112A）依上列之分析策略進行分析測試，結果可知儀器靈敏度（偵測到離子數/進樣之總鈾量）可達0.4，訊號強度可提高60倍；因此單一樣品之測量僅需標本量微至30 ng的鈾，同時，測量時間僅需15到20分鐘。除NBL 112A外，本研究亦採用另外兩種標準樣品HU1（Harwell Uranite）及石筍碳酸鈣CAVE-1共同監視測量精密度與準確度。結果顯示，所有標準樣品中234U（表示鈾同位素值）之單一測量精密度（within-run precision，±2 R.S.D.）小於3.3，而[238U] （表示鈾濃度）之單一測量精密度為3.1。長期測量234U的精密度（between-run precision，±2 R.S.D.）可小於4.1，至於[238U]之長期測量精密度則小於2.4。將測得之標準樣品234U值施行” t測試”，結果發現本研究測量值於95%可信度區間內（confidence level）與標準樣品之公認值（112A、HU1與CAVE-1的234U組成分別為-36.94、0 與2453）在統計上無顯著差異。
將上列的分析測量策略應用於測量台灣南灣之海水、秘魯之石筍與蘇門達臘之珊瑚標本等的測量分析上，結果顯示當鈾標本量大於30 ng時，234U之平均單一測量精密度約為5，[238U] 之平均單一測量精密度約為5.5。將這些天然樣品234U測量值執行“paired t test”，發現與HR-ICPMS之測值於統計上並無顯著差異，顯示本論文工作所致力突破的Q-ICPMS進行的鈾同位素值與濃度的測量在自然環境上的標本測量準確度已達一般HR-ICPMS之水準。
綜合言之，於本論文工作所提之策略下，四極桿式感應式耦合電漿質譜儀在量測標本中鈾濃度與鈾同位素值時，所需之鈾標本量僅30 ng，且測量精密度可達到千分等級（permil level），已達到高靈敏度與高精密度的測量目標。此分析策略之成功，對於應用於古海洋的研究課題上將可提供一個快速、低標本量、高精準度的測鈾方法；此外，未來再將此技術與策略應用於釷同位素值的測量，將可使鈾釷同位素在古海洋的研究上有更寬廣的應用。

Uranium isotopic composition and concentration have been widely applied to various fields in the earth sciences. This work focused on the improvement of analytical technique for uranium isotopic ratio and concentration measurements by Quadrupole Inductively Coupled Plasma Mass Spectrometer (Q-ICPMS). To approach the goal of permil-level analytical precision with only ng-U sample sizes, three strategies were applied. First, the Q-ICPMS was connected to a micro-concentric nebulization (MCN) introduction system to amplify sensitivity and to reduce required sample size. Standard deviation filters were then used to remove outliers to improve precision and accuracy. Finally, the 233U-236U double spikes were added and then data were processed with the standard bracketing method to correct mass fractionation and ratio drifting and, therefore, higher precision and accuracy could be achieved.
The results showed that the overall sensitivity (ion detected/ atoms introduced) was about 0.3~0.4. Oxide and hydride levels are less than 0.3% and 2 ppm, respectively. Under measurement time of 15-20 minutes, U standards with 30 ng of U give within-run precisions better than 3.3 (±2 R.S.D.) for 234U and better than 3.1 (±2 R.S.D.) for [238U]. Replicate measurements made on standards reveal that between-run precision of 4.1 (±2 R.S.D.) for 234U and 2.4 (±2 R.S.D.) for [238U] can be achieved. Measurements of U isotopic ratios and concentrations in coral, sea water, and speleothem samples show averaged 234U and [238U] within-run precisions of 5 and 5.5, respectively. All measurements made by this work reveal no significant difference from the values measured by High Resolution ICPMS (Li et al., 2005; X. Wang unpublished data) in the 95% confidence interval.

目錄
頁數
目錄 I
表目錄 II
圖目錄 III
中文摘要 IV
英文摘要 VII
第一章 簡介
1.1 自然界中鈾的同位素 1
1.2 自然界中鈾的濃度 2
1.3 自然標本鈾測量方法之簡介 3
1.4 研究目標 5
第二章 研究方法
2.1 儀器與材料 9
2.2 鈾同位素組成與鈾濃度之計算 10
第三章 結果與討論
3.1 儀器之靈敏度 20
3.2 測量方式 22
3.3 清洗步驟 23
3.4 數據處理 25
3.5 測量結果
3.5.1 標準樣品之測量結果 30
3.5.2 自然環境標本之測量結果 31
結論 56
參考資料 57
附錄 61
表目錄
頁數
表2-1 四極桿式感應耦合電漿質譜儀Agilent 7500s之設定參數 16
表2-2 微濃縮霧化系統CETAC MCN6000的設定參數 17
表3-1 儀器靈敏度之比較 34
表3-2 進樣速率與儀器靈敏度關係實驗數據 35
表3-3 Q-ICPMS測量方式之設定 36
表3-4 水與酸中鈾之訊號強度與濃度 37
表3-5-1 鈾標準樣品112A之測量數據 38
表3-5-2 鈾標準樣品HU1之測量數據 39
表3-5-3 鈾標準樣品CAVE1之測量數據 40
表3-6 Q-ICP測量鈾標準樣品234U之”學生-t”測試結果 41
表3-7 使用本方法時所需之天然樣品標本量 42
表3-8 天然樣品鈾同位素與鈾濃度測量結果 43
表3-9 不同儀器測量鈾方法之比較 44

圖目錄
頁數
圖1-1 鈾系不平衡年代回溯示意圖 7
圖1-2 質譜儀中質量分化設備示意圖 8
圖2-1 Agilent 7500s Q-ICPMS外觀與內部構造圖 18
圖2-3 CETAC MCN6000進樣系統外觀與內部構造圖 19
圖3-1 進樣速率、訊號強度與靈敏度關係圖 45
圖3-2 238U訊號與清洗時間關係圖 46
圖3-3 標本錐與漏形錐清洗前後之狀態 47
圖3-4 235U訊號強度隨測量時間變化圖 48
圖3-5 234U/235U與233U/235U比值隨測量時間之變動圖 49
圖3-6 原始測量與經過數據刪減所得U標準樣品112A之234U分佈圖 50
圖3-7 質量分異校正後之112A之234U重複測量分佈圖 51
圖3-8 標準樣品穿插校正前後之112A之234U重複測量分佈圖 52
圖3-9 重複測量標準樣品之U值分佈圖 53
圖3-10 重複測量標準樣品之U值分佈圖 54
圖3-11 自然界標本之鈾同位素值與鈾濃度測量值分佈圖 55

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