The inert gas radioactive isotope ^(85)Kr(with a half-life of 10.74 years), due to its stable physical and chemical properties, is an ideal tracer for shallow groundwater dating. In such a dating application, first th...The inert gas radioactive isotope ^(85)Kr(with a half-life of 10.74 years), due to its stable physical and chemical properties, is an ideal tracer for shallow groundwater dating. In such a dating application, first the dissolved gas is extracted from groundwater in the field, then krypton is separated from the gas sample, and finally the isotopic abundance ^(85)Kr/Kr will be determined by an ATTA instrument. According to the atmospheric input curve of ^(85)Kr, the ^(85)Kr age of groundwater is determined. We conducted ^(85)Kr analysis in three wells in Zhengding County on the plains in front of the Taihang Mountains, and made a comparison with tritium(~3H) method.展开更多
针对国内测量85Kr探测下限较高的现状,本文通过探测其衰变产生的β射线,设计并优化探测系统的本底和探测效率,实现对85Kr极低放射性浓度的测量。在探测器设计中,采用国产正比计数管作为4π主探测器,辅以铅铜屏蔽,以塑料闪烁体作为反符...针对国内测量85Kr探测下限较高的现状,本文通过探测其衰变产生的β射线,设计并优化探测系统的本底和探测效率,实现对85Kr极低放射性浓度的测量。在探测器设计中,采用国产正比计数管作为4π主探测器,辅以铅铜屏蔽,以塑料闪烁体作为反符合探测器。通过Geant4模拟研究正比计数管的探测效率,分析了其尺寸、工作气压对探测下限的影响,提出了优化方案。模拟结果表明,最佳的正比计数管参数为半径30 mm、长度100 mm,并在压强大于1 atm的条件下可有效提高探测效率至92%以上。塑料闪烁体反符合效率达90.29%,铅铜屏蔽厚度优化为外层8 cm、内层2 cm,屏蔽效率达99.5%。根据优化得到的主探测器的探测效率和探测系统的本底,计算出理论探测下限可达16.08 m Bq/m~3,比国内正比计数管的探测下限180 m Bq/m~3降低一个数量级。本研究为开发一种成本低、结构简单、性能可靠的^(85)Kr实时监测系统提供了重要的模拟参考和理论依据。展开更多
基金supported by the National Natural Science Foundation of China (41102151)Public Science and Technology Research Funds Projects of Ministry of Land and Resources(201511046)
文摘The inert gas radioactive isotope ^(85)Kr(with a half-life of 10.74 years), due to its stable physical and chemical properties, is an ideal tracer for shallow groundwater dating. In such a dating application, first the dissolved gas is extracted from groundwater in the field, then krypton is separated from the gas sample, and finally the isotopic abundance ^(85)Kr/Kr will be determined by an ATTA instrument. According to the atmospheric input curve of ^(85)Kr, the ^(85)Kr age of groundwater is determined. We conducted ^(85)Kr analysis in three wells in Zhengding County on the plains in front of the Taihang Mountains, and made a comparison with tritium(~3H) method.
文摘针对国内测量85Kr探测下限较高的现状,本文通过探测其衰变产生的β射线,设计并优化探测系统的本底和探测效率,实现对85Kr极低放射性浓度的测量。在探测器设计中,采用国产正比计数管作为4π主探测器,辅以铅铜屏蔽,以塑料闪烁体作为反符合探测器。通过Geant4模拟研究正比计数管的探测效率,分析了其尺寸、工作气压对探测下限的影响,提出了优化方案。模拟结果表明,最佳的正比计数管参数为半径30 mm、长度100 mm,并在压强大于1 atm的条件下可有效提高探测效率至92%以上。塑料闪烁体反符合效率达90.29%,铅铜屏蔽厚度优化为外层8 cm、内层2 cm,屏蔽效率达99.5%。根据优化得到的主探测器的探测效率和探测系统的本底,计算出理论探测下限可达16.08 m Bq/m~3,比国内正比计数管的探测下限180 m Bq/m~3降低一个数量级。本研究为开发一种成本低、结构简单、性能可靠的^(85)Kr实时监测系统提供了重要的模拟参考和理论依据。
