Study on the Method for Quartz Purification and Separation of Cosmogenic 10Be and 26Al in Samples from Fluvial Terraces
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摘要: 经历反复埋藏暴露演化过程的河流阶地样品，难以用常规方法将原生宇宙核素10Be、26Al有效分离。本文在前人实验方法基础上，使用人工挑选、磁选仪分选及酸洗方法，分离样品中碳酸盐、含铁矿物及大气生成的10Be，进一步优化了石英提纯实验流程。结果表明：长度为9 cm、内径为1 cm的阴离子交换树脂装置匹配4 mol/L氢氟酸淋滤液，可将B、Mg、Ca、Cr、Fe、Mn、Ni、Ti和Be、Al有效分离，Be、Al回收率分别可达95.7%、85.7%。阳离子交换树脂能有效分离Be、Al，两元素回收率均达到85%。获得10Be/9Be和26Al/27Al流程空白分别为2.19×10-15和1.63×10-15。优化后的实验方法显著提高了河流阶地样品中原生宇宙核素10Be、26Al的纯化效率，且10Be/9Be和26Al/27Al流程空白数值与国内外实验室具有可比性。采用本方法获得了成都平原冲积物10Be、26Al暴露年龄分别是76.36±9.51 ka和69.44±14.13 ka，为评价龙门山前缘隐伏断裂构造特征和活动性提供了年代学依据。Abstract: In situ produced 10Be and 26Al in fluvial terrace samples that have been repeatedly buried and exposed to the evolution process are difficult to separate using conventional methods. Based on prior experiments, 10Be in carbonate, iron-bearing mineral and 10Be produced in the atmosphere were separated by manual hand picking, magnetic separator sorting and acid washing methods, improving the procedure of purifying the quartz samples. The results show that anion exchange column, with a length of 9 cm and inner diameter of 1cm, matched 4 mol/L hydrofluoric acid leachate, can effectively separate B, Mg, Ca, Cr, Fe, Mn, Ni, Ti and Mn. The recoveries of Be and Al are 95.7% and 85.7%, resepectively. Be and Al can be separated by ion exchange very well which have recoveries up to 85%. The procedure blanks are 2.19×10-15 and 1.63×10-15 for 10Be/9Be and 26Al/27Al, respectively which are comparable with other labs. The exposure ages of Chengdu Plain alluvial elements are 76.36±9.51 ka for 10Be and 69.44±14.13 ka for 26Al, which provides a chronological basis for evaluating the structural features and activities of buried faults in the front of the Longmenshan.
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Key words:
- in situ-produced cosmogenic /
- 10Be /
- 26Al /
- recovery rate /
- Accelerator Mass Spectrometry
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表 1 磁选分选实验结果
Table 1. Results of magnetic separation test
实验次数 YNP-6 LJP-2 LJP-5 磁性物质
(g)非磁性物质
(g)磁性物质
(g)非磁性物质
(g)磁性物质
(g)非磁性物质
(g)第一次 26.4333 55.7304 3.7229 63.6846 4.8099 40.1229 第二次 28.2102 54.2930 3.8867 63.5003 4.9068 40.0190 第三次 28.5616 53.8987 3.9366 63.4504 4.9734 39.9179 第四次 28.8586 53.6108 3.9550 63.3902 4.9894 39.8935 第五次 28.9722 53.3898 3.9651 63.3963 4.9991 39.8771 
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表 2 阴离子交换树脂参数
Table 2. The parameters list of anion exchange resin
方法编号 阴离子交换树脂柱规格 淋滤液 方法1 内径1 cm，长度9 cm 盐酸：20 mL，10.2 mol/L 方法2 内径1 cm，长度9 cm 氢氟酸：36 mL，4 mol/L 方法3 内径1 cm，长度6 cm 氢氟酸：36 mL，4 mol/L 方法4 内径1 cm，长度3 cm 氢氟酸：36 mL，4 mol/L 方法5 内径0.6 cm，长度9 cm 氢氟酸：36 mL，4 mol/L
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表 3 本项目与中国科学院地球化学研究所回收率实验结果对比
Table 3. A comparison of recoveries of the elements
实验室 元素回收率(%) Be Al B Mg Ca Cr 本项目组 95.7 85.7 - 39.7 59.0 6.57 中国科学院地球化学研究所[30] 93.2 93.0 62.5 94.2 87.2 86.8 注：“-”表示未检测到元素含量。
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表 4 不同实验室的流程空白值比较
Table 4. A comparison of blank values obtained by different laboratories
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表 5 加速器质谱仪分析结果
Table 5. Results of samples measured by AMS
样品编号 石英质量(g) 9Be载体质量(g) 10Be/9Be 绝对误差 26Al/27Al 绝对误差 SV1-300 25.00 305.5 1.29×10-13 1.56×10-14 2.13×10-13 3.95×10-14 SV3-230 25.34 308.8 5.55×10-13 1.42×10-14 1.99×10-12 7.56×10-14 SV4-200 25.03 307.8 2.38×10-13 7.71×10-15 1.32×10-12 5.12×10-14 SV5-155 25.21 307.6 4.10×10-13 1.03×10-14 3.28×10-12 1.31×10-13 SV6-120 25.15 307.6 5.01×10-13 1.73×10-14 2.72×10-12 1.66×10-13 SV7-80 25.19 306.2 9.30×10-13 2.95×10-14 4.78×10-12 1.58×10-13 SV8-40 25.00 307.6 8.94×10-13 2.52×10-14 3.15×10-12 8.36×10-14
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