U-238,U-234 AND TH-232 IN SEAWATER
U-238,U-234 AND TH-232 IN SEAWATER
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DOI：
10.1016/0012-821x(86)90108-1
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发表时间：
1986-11-01
影响因子：
5.3
通讯作者：
WASSERBURG, GJ
中科院分区：
文献类型：
--
作者：
CHEN, JH;EDWARDS, RL;WASSERBURG, GJ
我们开发了通过同位素稀释质谱法测定海水中 238 U、234 U 和 232Th 浓度的技术。 U 测量使用 233U 单键 236U 双尖峰进行，以校正仪器分馏。对铀标准的测量表明，234U/238U 比率可以准确且可重复地测量。对于 5 × 109 个 234U 原子样品（3 × 10−8g 总 U，10 ml 海水），可以常规测量 234U/238U，精度为 ± 5‰ (2σ)。数据采集时间约为 1 小时。样本量小、精度高、数据采集时间短，优于 α 计数技术。对于 8 × 1012 个 238U 原子的样品（∼ 3 × 10−9g U，1 ml 海水），238U 的测量结果为 ± 2‰ (2σ)。对于 3 × 1011232Th 原子 (10−10g232Th, 1)，232Th 的测量结果为 ± 20‰。 1 海水）。这种小样本量将极大地促进海洋中 232Th 浓度的调查。利用这些技术，我们测量了大西洋未过滤酸化海水垂直剖面中的 238 U、234 U 和 232Th，以及太平洋垂直剖面中的 238 U 和 234 U。大西洋（7°44′N，40°43′W）和太平洋（14°41′N，160°01′W）海洋0～4900 m深度处234U/238U的测定结果在实验误差（±5‰，2σ）内相同。这些 234U/238U 测量值的平均值比平衡比率 5.472 × 10−5 高 144 ± 2‰ (2σ)。 U 浓度（标准化为 35‰ 盐度）范围为 3.162 至 3.281 ng/g，范围为 3.8%。太平洋样本（北纬 31°4′，西经 159°1′）的平均浓度比大西洋（北纬 7°44′，西经 40°43′ 和北纬 31°49′，西经 64°6′）的平均浓度高约 1%。大西洋剖面的 232Th 浓度范围为 0.092 至 0.145 pg/g。观察到的 234U/238U 比率的恒定性与使用简单的二- 模型预测的 234U/238U 范围以及由 14 C 确定的深水在海洋中的停留时间一致。盐度归一化的铀浓度的变化表明，铀在海洋环境中的反应性可能比之前想象的要高得多。
We have developed techniques to determine238U,234U and232Th concentrations in seawater by isotope dilution mass spectrometry. U measurements are made using a233Usingle bond236U double spike to correct for instrumental fractionation. Measurements on uranium standards demonstrate that234U/238U ratios can be measured accurately and reproducibly.234U/238U can be measured routinely to ± 5‰ (2σ) for a sample of 5 × 109atoms of234U (3 × 10−8g of total U, 10 ml of seawater). Data acquisition time is ∼ 1 hour. The small sample size, high precision and short data acquisition time are superior toα-counting techniques.238U is measured to ± 2‰ (2σ) for a sample of 8 × 1012atoms of238U (∼ 3 × 10−9g of U, 1 ml of seawater).232Th is measured to ± 20‰ with 3 × 1011232Th atoms (10−10g232Th, 1 1 of seawater). This small sample size will greatly facilitate investigation of the232Th concentration in the oceans. Using these techniques, we have measured238U,234U and232Th in vertical profiles of unfiltered, acidified seawater from the Atlantic and238U and234U in vertical profiles from the Pacific. Determinations of234U/238U at depths ranging from 0 to 4900 m in the Atlantic (7°44′N, 40°43′W) and the Pacific (14°41′N, 160°01′W) Oceans are the same within experimental error (± 5‰,2σ). The average of these234U/238U measurements is 144 ± 2‰ (2σ) higher than the equilibrium ratio of 5.472 × 10−5. U concentrations, normalized to 35‰ salinity, range from 3.162 to 3.281 ng/g, a range of 3.8%. The average concentration of the Pacific samples (31°4′N, 159°1′W) is ∼ 1% higher than that of the Atlantic (7°44′N, 40°43′W and 31°49′N, 64°6′W).232Th concentrations from an Atlantic profile range from 0.092 to 0.145 pg/g. The observed constancy of the234U/238U ratio is consistent with the predicted range of234U/238U using a simple two-☐ model and the residence time of deep water in the ocean determined from14C. The variation in salinity-normalized U concentrations suggests that U may be much more reactive in the marine environment than previously thought.