研究报告
万国江,吴丰昌,万恩源,廖海清,YMasatoshi,王长生.239+240Pu作为湖泊沉积物计年时标:以云南程海为例[J].环境科学学报,2011,31(5):979-986
239+240Pu作为湖泊沉积物计年时标:以云南程海为例
- 239+240Pu as a dating marker in lake sediments:An example from Lake Chenghai,China
- 基金项目：国家自然科学基金(No.40873086,40773071)
- 作者
- 单位
- 万国江
- 中国科学院地球化学研究所环境地球化学国家重点实验室, 贵阳 550002
- 吴丰昌
- 中国环境科学研究院国家环境保护湖泊污染控制重点实验室, 北京 100012
- 万恩源
- Nakaminato Laboratory for Marine Radioecology, National Institute of Radiological Sciences, 3609 Isozaki-cho, Hitachinaka, Ibaraki, 311-1202 Japan
- 廖海清
- 中国科学院地球化学研究所环境地球化学国家重点实验室, 贵阳 550002
- YMasatoshi
- 中国环境科学研究院国家环境保护湖泊污染控制重点实验室, 北京 100012
- 王长生
- Nakaminato Laboratory for Marine Radioecology, National Institute of Radiological Sciences, 3609 Isozaki-cho, Hitachinaka, Ibaraki, 311-1202 Japan
- 摘要：在近代沉积作用领域137Cs时标与210Pb计年结合,获得了广泛而有效的应用.然而,137Cs经过两个半衰期的衰变已难于辩识.环境中的Pu核素具有相对较长的半衰期,也随全球大气扩散而散落于地球表面,可望作为沉积计年的时间标志.通过程海沉积物柱芯中239+240Pu比活度、240Pu/239Pu原子比率及校正到沉积年代的137Cs比活度的对比研究表明:二者比活度的垂直剖面基本相似、239+240Pu比活度与北半球137Cs逐年沉降量之间也具有很好的对应关系,显示出239+240Pu同样具有湖泊沉积计年的时标价值.不同层节沉积物中,239+240Pu/137Cs的平均值为0.016;∑239+240Pu/∑137Cs=0.012,与全球大气散落沉降的活度比相近.239+240Pu/137Cs活度比的垂直变化,寓意出239+240Pu在沉积物中较137Cs具有更小的扩散迁移能力.240Pu/239Pu原子比率平均值为0.195±0.021,显示240+239Pu主要来自全球大气散落沉降;沉积物8cm深度出现的异常点,显示出切尔诺贝利核事故影响的痕迹.
- Abstract：137Cs time mark combined with 210Pb dating has been widely applied to recent sedimentation.The 137Cs specific activity is,however,hard to detect after decay for two half-lifes.Due to its comparatively long-term half-life,plutonium from global fallout is expected to provide a dating mark for sedimentation.In the present work,we discuss the vertical distribution of 239+240Pu and 137Cs specific activities,and the 240Pu/239Pu atom ratio in a sediment core of Lake Chenghai.The distribution pattern of 239+240Pu was similar to those of 137Cs specific activities(decay corrected to deposition time)in the sediment core,and also corresponded well with the annual deposition of 137Cs in the northern hemisphere.These results demonstrate that the 239+240Pu specific activity is available to construct recent chronology for lacustrine sediment.In the examined sediment core,the values of 0.016 for average 239+240Pu/137Cs activity ratio and 0.012 for ∑239+240Pu/∑137Cs,are close to that of global fallout.The vertical variation of 239+240Pu/137Cs activity ratio indicated that the postdepositional transport of plutonium is much less than radiocesium.The average 240Pu/239Pu atom ratio is 0.195±0.021,which means plutonium in Lake Chenghai originated from global fallout.The abnormal distribution of 239+240Pu and 137Cs at 8 cm in the sediment core may be explained by the influence of Chernobyl-source radionuclides.
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