碩士 / 國立中山大學 / 海洋地質及化學研究所 / 92 / 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.
| Identifer | oai:union.ndltd.org:TW/092NSYS5271007 |
| Date | January 2004 |
| Creators | Chun-Yen Wang, 王春燕 |
| Contributors | Yu-Chia Chung, 鍾玉嘉 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 72 |
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