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題 名 | Radioactive Disequilibria among [94a4]Ra, [94a7]Pb and [94a7]Po at the sea off Northeastern Taiwan=臺灣東北外海中鐳-226, 鉛-210及釙-210間之放射不平衡 |
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作 者 | 鍾玉嘉; 吳佑民; | 書刊名 | 臺灣海洋學刊 |
卷 期 | 34:4 民84.12 |
頁 次 | 頁15-29 |
分類號 | 351.9 |
關鍵詞 | 黑潮邊緣交換作用; 放射不平衡; 鐳-226; 鉛-210; 釙-210; 顆粒態; 溶解態; 平均駐留時間; 臺灣東北海域; KEEP; Radioactive disequilibria; [94a4]Ra; [94a7]Pb; [94a7]Po; Particulate phase; Dissolved phase; Mean residence time; Northeastern Taiwan; |
語 文 | 英文(English) |
中文摘要 | 於臺灣東北外海同時量測溶解態及顆粒態之鉛-210與釙-210和鐳-226的結果,表 水之鉛-210及釙-210均向陸棚遞減,反應出陸棚區對此二核種有較高效之移除。利用盒子模 式並以20米為混合層之平均厚度計算鉛-210及釙-210之下移通量,分別得到2及0.25dpm cm-2y-1. 此區由大氣鉛-210所形成之超量鉛-210可穿透水柱至約200-300米深。在此水深之下, 鉛-210因沈降顆粒之清除作用而呈不足現。 鉛-210/鐳-226活性比,依據三組鉛-210及鐳-226剖面,由表水之1.8降至深水之0.3。 在鉛-210不足之下層水中鉛-210相對於清除作用之平均駐留時間在13至78年之間。 依據釙-210與鉛-210之放射不平衡狀態,本區水柱可分成三層,即釙-210相對於鉛-210 呈不足之上層,釙-210呈超量之中層和釙-210又呈不足之下層。由各層之質量平衡計算結果 鉛-210均不再循環,但釙-210於此溶解,還須側向輸入。由釙-210剖面與鹽度資料研判,在 棚裂或上部斜坡區有較佳之垂直混合作用,且有鉛-210由陸棚區向陸坡區傳輸。 顆粒態鉛-210隨深度增加,即由淺水佔全量鉛-210之10%增至深水佔20%;顆粒態釙-210 則由淺水及中層水佔全量釙-210之13%增至深水佔50%。此二核種在顆粒之含量向下增加之現 象與在邊緣海中高反應度核種易被顆粒物清除的說法吻合。 |
英文摘要 | 210Pb and 210Po in particulate and dissolved phases as well as 226Ra were measured at the sea off northeastern Taiwan. Both 210Pb and 210Po in surface water decrease toward the shelf, reflecting more efficient removal of the nuclides in the shelf area. Box-model calculations show that the vertical fluxes of 210Pb and 210Po out of the surface layer in this area are, respectively, 2 and 0.25 dpm cm-2y-1 if one takes this layer to be 20m. The atmospheric 210Pb as an excess over 226Ra in the water column of the area may penetrate to a depth of about 200 to 300m . Below this depth, 210Pb becomes deficient due to scavenging by settling particulates. The 210Pb/226Ra activity ratio based on three pairs of 210Pb and 226Ra Profiles ranges from 1.8 in shallow water to 0.3 in deep water. The mean scavenging residence time for 210Pb in the layer with 210Pb deficiency varies between 13 and 78 yrs. Based on the radioactive disequilibrium observed between 210Po and 210Pb, the water column may be divided into three layers: an upper layer with 210Po deficiency relative to 210Pb; an intermediate layer with 210Po excess over 210Pb, and a lower layer with deficient 210Po rather than in equilibrium with 210Pb. based on mass balance calculations for each layer, 210Pb is not recycled at all while 210Po in the intermediate layer requires a lateral input in addition to a total recycling or dissolution of particulate 210Po sinking from the upper layer. The 210Pb profiles together with salinity data suggest a better vertical mixing at the shelf break and/or the upper slope, and also a lateral transport of 210 Pb from the shelf to the slope. Particulate 210Pb increases with depth from about 10% of the total 210Pb in shallow water to about 20% in deep water, particulate 210Po increases from about 13% of the total 210Po in shallow and intermediate water to about 50% in deep water. These downward increases of both nuclides in the particulate portion are consistent with the scavenging of reactive nuclides by particulates at the marginal sea. |
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